EPS2005, Session P-2 Abstracts - CIEMAT · Feasibility study for a blow-off technique to real time monitor dust particles in fusion plasmas P-2.086 DavidRapisarda An investigation

EPS2005, Session "P-2" Abstracts

Session Author PosterTitle

P-2.001 M.Tsalas Divertor plasma drift patterns at ASDEX Upgrade

P-2.002 AlbertoAlfier Influence of ELMs on Edge Temperature and Density Profiles in TCV

P-2.003 L.Carraro Impurity behaviour and radiation pattern in the RFX- mod reversed field pinch

P-2.004 M.Rubel Material Migration Studies at JET Using Tracer Techniques

P-2.005 M.BecouletComparative Modeling of Type I ELM control by stochastic fields in DIII-D, JET and ITER.

P-2.006 EmiliaR.Solano ELM calorimetry in JET

P-2.007 AlbertoLoarteInfluence of toroidal field direction and plasma rotation on pedestal and ELM characteristics in JET ELMy H-modes

P-2.008 D.L.Hillis Tritium pathways in JET trace tritium transport experiments

P-2.009 T.P.Kiviniemi Ripple-Induced Fast Ion and Thermal Ion Losses

P-2.010 S.BrezinsekIn situ measurement of chemical erosion yields for the production of C2Hy in the JET outer divertor

P-2.011 A.Pospieszczyk Molecular H/D/T sources in JET

P-2.012 A.J.Meakins Applying Advanced Statistical Techniques to Tokamak L-H Threshold Data

P-2.013 W.Fundamenski ELM-limiter interaction on JET

P-2.014 G.Y.Antar Gas Jets and Their Interaction With Magnetically Confined Plasmas

P-2.015 S.Jachmich Divertor particle and power deposition profiles in JET ELMy H-mode discharges

P-2.016 L.N.Khimchenko Fractal growth of dust and globular films in T-10 tokamak.

P-2.017 RozhanskyImpact of Magnetic Configuration on Edge Radial Electric Field MAST-ASDEX Upgrade Simulation with B2SOLPS5.0

P-2.018 L.G.Eliseev Investigation of the plasma potential behaviour at the edge of the T-10 tokamak by HIBP

P-2.019 A.Kendl Influence of flux surface shape on DALF and ITG edge turbulence

P-2.020 M.F.HeynOn the Interaction of a Rotating Magnetic Field with the Plasma in the Kinetic Approximation

P-2.021 V.YavorskijModelling of combined effect of TF ripples and MHD perturbations on fast ion behaviour in tokamaks

P-2.022 T.P.Kiviniemi Full f particle simulation of internal transport barrier formation

P-2.023 S.V.Henriksson Characteristics of fluctuations in ELMFIRE simulations

P-2.024 U.StrothOn magnetic fluctuations and parallel dynamics of drift wave turbulence in the torsatron TJ-K

P-2.025 O.Marchuk Impurity transport studies in TORE SUPRA with He-like spectroscopy

P-2.026 C.F.Maggi Edge and core confinement in improved H-modes in ASDEX Upgrade

P-2.027 G.D.ConwayObservations on core turbulence and radial electric field transitions in ASDEX Upgrade using Doppler reflectometry

P-2.028 G.Tardini Ion ITB dynamics in ASDEX Upgrade

P-2.029 W.Suttrop Machine independent representation of experimental H-mode pedestal and divertor data

P-2.030 H.Thomsen Pattern recognition techniques in plasma turbulence imaging

P-2.031 A.Kraemer-FleckenEdge Turbulence Studies At Textor During Dynymic Ergodic Divertor Operation By Means Of Reflectometry

P-2.032 D.Reiser Turbulent transport in the plasma edge in the presence of static stochastic magnetic fields

P-2.033 S.JachmichEffects of edge ergodization induced by DED on turbulence and particle transport in TEXTOR

P-2.034 K.Rypdal Profile robustness and routes to turbulence in the helimak configuration

P-2.035 T.T.RibeiroGyrofluid turbulence computations in the edge and SOL regions of tokamak plasmas using realistic magnetic field geometry

P-2.036 H.Figueiredo Study of edge flows and transport during emissive electrode biased discharges on ISTTOK

P-2.037 C.Silva Transport and fluctuations during electrode biasing on TJ-II

P-2.038 P.Strand Effects of impurities on drift wave particle transport

P-2.039 M.AnsarMahmood Unstable Ion-Temperature-Gradient Modes in ITER Geometry

P-2.040 V.P.Pavlenko Large scale flows and coherent structure phenomena in flute mode turbulence

P-2.041 I.G.J.Classen 2D temperature profiles of DED structures using ECE-Imaging in TEXTOR

P-2.042 M.DeBockInfluence of an ergodic field in the plasma edge on the global plasma rotation at the TEXTOR tokamak

P-2.043 HugoJ.deBlank Temperature gradient effects on magnetic stochastization

P-2.044 W.Zwingmann Equilibrium reconstruction of tokamak discharges with toroidal variation

P-2.045 M.-C.Firpo Non-ideal MHD effects on the nonlinear growth of m 1 internal modes

P-2.046 A.Sen Neoclassical tearing modes in the presence of sheared flows

P-2.047 A.SenguptaStatistical Analysis of the equilibrium configurations of W7-X stellarator using Function Parametrization

P-2.048 K.Hayase First Result from a New RFP Device with Very Small Aspect Ratio

P-2.049 M.Takechi MHD instabilities observed in extreme reversed shear discharges on JT-60U

P-2.050 T.Ozeki Modeling of MHD Stability Consistent to the Transport

P-2.051 Y.NakamuraSimulation Modeling of Fully Non-Inductive Buildup Scenario in High Bootstrap Current Tokamaks without Center Solenoids

P-2.052 S.Sakakibara Configuration Dependence of MHD Activities in high-beta regime of LHD

P-2.053 Y.Narushima Experimental study of current driven MHD mode in LHD

P-2.054 Y.HiranoReproducible Appearance of Quasi Single Helicity State in a Reversed Field Pinch with an Appropriate Control of the Reversed Toroidal Field.

P-2.055 L.FrassinettiRole of the m 0 magnetic perturbations in the crash phase of the pulsed polidal current drive regime in the TPE-RX device

P-2.056 S.Shiina Relaxed State of Reversed Field Pinch Equilibrium with Low Aspect Ratio

P-2.057 K.Saito MHD Stability Analysis and Edge control of the ATRAS-RFP Plasma

P-2.058 MasayoshiNagataPlasma flow injection into a torus chamber as a new approach to flowing two-fluid plasma generation

P-2.059 O.Sauter Partial Stabilisation of NTMs with ECCD for standard scenarios in ITER

P-2.060 C.G.Gimblett A model for the evolution of current-driven ELMs

P-2.061 D.F.Howell Locked mode thresholds on the MAST spherical tokamak

P-2.062 I.T.Chapman Stabilisation of Sawteeth in MAST by Toroidal Rotation

P-2.063 G.W.PacherSimulation of ITER Improved H-mode Operation with the Integrated Core Pedestal SOL Model Using MMM95 and GLF23 Core Transport Models

P-2.064 F.Saint-Laurent Disruption Mitigation Experiment on Tore Supra

P-2.065 R.GuirletOn the stationarity of the intrinsic impurity content in the bulk of Tore Supra long discharges

P-2.066 H.Utoh Biasing Experiments by a Ti Electrode in the Tohoku University Heliac

P-2.067 M.SugiharaExtrapolation of Plasma Current Quench Time during Disruptions from Existing Machines to ITER

P-2.068 Y.Kawano Characteristics of Runaway Plasmas in JT-60U

P-2.069 Y.Miura Burn control study using burning plasma simulation experiments in JT-60U

P-2.070 T.Akiyama Edge Transport Barrier Formation and Power Threshold Properties in CHS

P-2.072 V.E.Lukash Combined DINA-CH and CRONOS Simulations of ITER

P-2.073 V.N.Dokuka Free Boundary Simulations of ITER Scenarios

P-2.074 V.Weinzettl Fast bolometry on the CASTOR tokamak

P-2.075 V.PifflTemporally and spatially resolved measurements of VUV lines intensity in the CASTOR tokamak

P-2.076 I.DuranProgress in evaluation of radiation-hard galvanomagnetic devices for use in the ITER magnetic diagnostic

P-2.077 G.Anda Li-beam developments

P-2.078 S.Kálvin Investigation of pellet-plasma interaction on ASDEX Upgrade

P-2.079 K.-S.Chung Effect of ion-neutral collision on the deduction of plasma flow velocity

P-2.080 JunGyoBak Integrator for the KSTAR magnetic diagnostics

P-2.081 S.G.Lee Fabrication details for the KSTAR magnetic diagnostics

P-2.082 M.Kocan A new probe for ion temperature measurements in the tokamak scrape-off layer

P-2.083 T.Estrada Fluctuation Measurements by Reflectometry in the Stellarator TJ-II

P-2.084 A.Hidalgo Self-consistent modelling of supersonic He beam attenuation in the TJ-II Edge Plasmas

P-2.085 BernardoZurroFeasibility study for a blow-off technique to real time monitor dust particles in fusion plasmas

P-2.086 DavidRapisardaAn investigation of the relationship between toroidal rotation and bootstrap current in the TJ-II stellarator

P-2.087 E.BlancoStudy of Doppler reflectometry viability in TJ-II stellarator using a 2- dimensional full-wave code

P-2.088 J.HerranzInfluence of the stray light upon TJ-II Thomson scattering profiles measured in different magnetic configurations.

P-2.089 J.M.CarmonaA code to simulate neutral beams across TJ-II for the exploitation of a charge-exchange recombination spectroscopy diagnostic

P-2.090 J.VegaApplication of intelligent classification techniques to the TJ-II Thomson Scattering diagnostic

P-2.091 M.Sánchez Relevant improvements in the two color interferometer diagnostic in TJ-II Stellarator

P-2.092 D.L.Brower Laser-Based Polarimetry and Interferometry Measurements in a High-Temperature Plasma

P-2.093 J.A.KingCharacterization of Ti Ká radiation resulting from interaction of a highly intense laser pulse with a thin titanium foil

P-2.094 ShiZhongbingObservations of the cold pulse propagation during multi-pulse molecular beam injection on HL-2A

P-2.095 V.Petrzilka Electron Acceleration Near ICRF Antennae

P-2.096 V.PetrzilkaFast Particle Energy Measurements in the Scrape-off Layer During Lower Hybrid Current Drive on Tore Supra

P-2.097 E.Belonohy High Field Side Penetration Depth Scaling at ASDEX Upgrade

P-2.098 K.GálSimulation of Pellet Induced Perturbations in Fusion Plasmas for Fueling and ELM Triggering Scenarios

P-2.099 A.Cappa Experimental dependence of plasma breakdown on wave polarization in the TJ-II stellarator

P-2.100 G.Fiksel Neutral Beam Injection and Fast Ion Confinement in the MST Reversed Field Pinch

P-2.101 V.S.ChanSimulation of Fast Alfven Wave Interactions With Neutral-Beam and Minority Ions in Tokamaks

P-2.102 L.R.Baylor Pellet Injection From Different Locations on DIII-D and Extrapolation to ITER

P-2.103 YijunLinObservation and Modeling of Ion Cyclotron Range of Frequencies Waves in the Mode Conversion Region of Alcator C-Mod

P-2.104 J.A.GoetzAuxiliary Heating and Current Drive Systems for the Madison Symmetric Torus Reversed Field Pinch

P-2.105 H.K.Na Poloidal H-alpha monitor and visible TV system design for long diagnostic port of KSTAR

P-2.106 J.Dies Safety analysis of abnormal fueling in ITER using SAFALY

P-2.107 G.Vlad Source Regulation of Fast Energetic Particle Driven Alfvén Modes Dynamics

P-2.108 M.Cavenago A simulation code for the extraction of H- ions

P-2.109 G.DeTommasi Identification of a dynamic model of plasma current density profile

P-2.110 X.Bonnin B2-Eirene SOLPS Modelling of JET SOL plasma flow

P-2.111 S.Sipilä Guiding-centre simulations of ion orbit loss heat loads on JET divertor targets

P-2.112 A.Huber Modelling JET divertor physics with the EDGE2D Code

P-2.113 D.Pilipenko Transport balance of RF-heated impurity ions

P-2.114 K.M.Rantamäki Effect of density fluctuations on lower hybrid ray tracing and q-profile

P-2.115 A.N.SavelievApproximate relativistic dispersion relation for electron Bernstein waves in inhomogeneous plasma

P-2.116 V.A.Rantsev-Kartinov Radial Electric Field in Toroidal Systems and a Thermoelectric Field of Plasma

P-2.117 A.B.KukushkinSelf-Consistent Simulation of Electron Cyclotron Radiation Transport and Superthermal Electron Kinetics in Hot Tokamak Plasmas

P-2.118 L.K.KuznetsovaEffect of ECCD/ECRH-Produced Superthermal Electrons on Electron Cyclotron Radiation Transport in Hot Tokamak Plasmas

P-2.119 V.E.Zhogolev Simulation of Heavy Impurities Transport and Radiation for ITER Scenarios

P-2.120 A.A.Subbotin Alpha-particle Confinement and Conservation of Second Adiabatic Invariant

P-2.121 Yu.V.Gott The Charged Particle Distribution

P-2.122 N.B.Rodionov Numerical study of high-frequency ICRF heating at T11-M and KTM tokamaks

P-2.123 G.G.GladushNumerical investigation of a tokamak used as the volumetric neutron source for material tests

P-2.124 A.V.Tykhyy Influence of electric fields on the energetic particle orbits in stellarators

P-2.125 V.V.Lutsenko Analysis and interpretation of observations of Alfvénic activity in Wendelstein 7-AS

P-2.126 S.K.Zhdanov Impact of structural inhomogeneity on waves in a 2D complex plasma

P-2.127 A.A.Samarian Large-amplitude oscillations of dust particles in a plasma sheath

P-2.128 A.Zobnin A Boundary Structure of Dusty Cloud

P-2.129 LydiaJohnson Experiments with Microrods in an RF Plasma Sheath

P-2.130 R.Kompaneets Dust-lattice waves Role of charge variations and anisotropy of dust-dust interaction

P-2.131 S.A.Maiorov The reactive ion-drag force in dusty plasmas

P-2.132 T.Antonova Attractive force in 3D plasma clusters

P-2.133 F.M.Cheung Coulomb Clusters Stability and Spectrum of Energy States

P-2.134 S.Khrapak Effect of ion-neutral collisions on particle charge in gas-discharge plasmas

P-2.135 M.KretschmerThe trampoline effect - distribution of forces inside the void region of a complex plasma in microgravity

P-2.136 O.S.Vaulina Study of Relation between Transport Coefficients in Dusty Plasma Systems

P-2.137 M.KretschmerForces and effective potential energy inside the void region of a complex plasma in microgravity

P-2.138 S.A.Maiorov Interaction between grains in plasma

P-2.139 S.Sobhanian Reabsorption of Langmuir waves generated by a hot electron beam propagating in a plasma

P-2.140 D.P.KostomarovOn the transformation of structurally unstable magnetic configuration into structurally stable one

P-2.141 F.Califano Propagation of finite amplitude disturbances in an inhomogeneous magnetized plasma

P-2.142 FrancescoCalifano Role of numerical dissipative effects in collisionless plasmas simulations

P-2.143 M.Cercek Sheath formation in a two-electron temperature plasma

P-2.144 K.Bendib-Kalache Weibel instability due to the inverse bremsstrahlung absorption

P-2.145 S.ChoEffects of the magnetic field and the thermal electron motion on characteristics of guided-wave-sustained plasmas

P-2.146 L.Chacón A fully implicit 3D extended MHD algorithm

P-2.147 NikolaJelic Particle in cell simulation of a Tonks-Langmuir model

P-2.148 Y.Kominis Particle interactions with solitary waves in magnetized plasmas

P-2.149 L.VlahosNon-linear excitation of magnetosonic waves through gravitational waves in strongly magnetized plasmas

P-2.150 G.BonhommeSelecting, characterizing, and acting on drift waves and flute modes turbulence in a low-beta magnetized plasma column

P-2.151 S.TeodoruIs the plasma at a plane probe unstable in the presence of fast electrons producing secondary electrons

P-2.152 B.CoppiConsistency of the Accretion Theory of the Spontaneous Rotation Phenomenon with Recent Experiments

P-2.153 O.Maj Beam Tracing solution of the weakly nonlinear Burgers' equation

P-2.154 L.CondeA ionization instability in weakly ionized unmagnetized plasma with negatively charged dust grains

P-2.155 V.A.Rantsev-Kartinov Revelation of the Sun Self-Similarity Skeletal Structures

P-2.156 S.-I.Itoh On periodic change of differential rotation and global magneto-fluid structure of the sun

P-2.157 B.Dromey Bright XUV harmonic generation in the water window.

P-2.158 D.Dorranian Microwave Emission from Magnetized Wake of Laser Irradiated Gas Jet

P-2.159 S.Gammino High density ECR plasmas for the production of intense highly charged ion beams

P-2.160 M.TanimotoGeneration of monoenergetic electron beams in a plasma-wave potential driven by an intense laser pulse

P-2.161 E.d'Humières Optimization of proton beams created by laser-plasma interaction for various applications

P-2.162 A.Lifschitz Laser wakefield acceleration of electron bunches in the mildly nonlinear regime

P-2.163 E.Brambrink Detailed studies of the transverse beam characteristics of laser produced ion beams

P-2.164 F.Fiuza Detailed study of the photon accelerator

P-2.165 J.L.Martins Explosion Dynamics of Heterogeneous Nanoplasmas

P-2.166 J.F.Vieira Optimizing wave breaking and self injection in the laser wake field accelerator

P-2.167 V.V.KulaginControllable generation of a single attosecond relativistic electron bunch by a superintense laser pulse with a sharp rising edge

P-2.168 H.Suk Generation of relativistic high-energy electrons by laser wakefield acceleration at KERI

P-2.169 M.Marti Physics of the formation of collisionless shocks

P-2.170 E.d'Humières New setups to improve proton acceleration with high intensity lasers

P-2.171 N.Lemos Design and characterization of gas jets for laser-plasma interaction

P-2.172 C.D.Murphy Laser Wakefield Acceleration of Photons

P-2.173 M.Schnürer Field-shielding in femto- and picosecond laser accelerated ion beams

P-2.174 P.V.Nickles Particle acceleration with ultrashort light pulses

P-2.175 M.Geissler 3d-Pic Simulations Of Laser Electron Acceleration

P-2.176 O.KlimoNumerical Study of K-alpha Emission from the Backside of Foil Targets Irradiated by Ultrashort Laser Pulses

P-2.177 A.RusanovInteraction of an electron beam with magnetized semiconductor plates in a rectangular waveguide

P-2.178 M.Grech Laser beam smoothing in plasma at powers below the filamentation threshold

Divertor plasma drift patterns at ASDEX Upgrade

M. Tsalas 1, N. Tsois 1, V. Bobkov 2, H. W. Muller 2, J. Neuhauser 2, V. Rohde 2 and the

ASDEX Upgrade Team 2

1 NCSR Demokritos , Inst. of Nucl. Technology Rad. Prot., Attica, Greece2 Max Planck Institut für Plasmaphysik, EURATOM Association, Garching, Germany

Studying the plasma flow in the scrape-off layer (SOL) and divertor is crucial, not only to

determine the particle and power flow towards the divertor plates, but also to understand

impurity transport and migration between the main chamber and divertor. Measurements in

the mid-plane must be complemented by (and be consistent with) measurements in the

divertor, where the picture is further complicated by the outer SOL / private flux / inner SOL

interaction, by the coupling with the recycling neutrals and, in H-mode discharges, by

transients (e.g. flow reversals during ELM s etc.).

In ASDEX Upgrade, a reciprocating probe run by NCSR Demokritos , installed in the

divertor region and capable of measuring the plasma in both the inner and outer SOL (just

below the x-point) and the private flux, was equipped with a directional (Mach) probe head

and a fast (100 kHz) data acquisition system and used to study flow patterns and fluctuations

in these three regions. We report on our observations, made in ohmic discharges under both

attached and detached conditions and in H-mode discharges.

Using the actual saturation current measurement from the mach tips to determine the

separatrix position with higher accuracy than that obtained from magnetic reconstruction, we

show that in ohmic discharges during a horizontal scan of the probe the drift velocity in the

low field side (LFS) SOL initially decreases, reaching a minimum value of approximately M

~ 0.3 in the middle of the LFS SOL, before increasing suddenly over a distance of only

about 1 cm to approximately M ~ 1 as the separatrix is crossed. We also show how the flow

reversal position in the private flux depends on the divertor attachment conditions. The drift

velocity measured during the probe s HFS separatrix crossing is not as large as at the LFS

separatrix (of the order of M ~ 0.5), but then it increases rapidly in the HFS SOL, typically

exceeding M = 1.

In H-mode discharges, we report on the measured fluctuations during type I and type III

ELM s, comment on the observed flow reversals and compare these with observations from

other machines.

Finally, we discuss our results relevance to the current SOL flow models and comment on

how the measured flows can influence the impurity migration and the deposition patterns

observed at the divertor plates.

P-2.001, Tuesday June 28, 2005

Influence of ELMs on Edge Temperature and Density Profiles in TCV

A. Alfier 1,2, R. Behn3, P. Nielsen2, R. Pasqualotto2, G. Zhuang3, Y. Martin3, K. Schombourg3 1Università degli Studi di Padova, Dipartimento di Fisica G. Galilei, Padova, Italia

2Consorzio RFX, Associazione Euratom-Enea sulla Fusione, Padova, Italia 3EPFL,Centre de Recherches en Physique des Plasmas,

Ass. Euratom-Confédération Suisse, Lausanne, Switzerland

Investigation of the evolution of electron density and temperature near the plasma edge during

H-modes requires good spatial resolution to resolve the gradients. For this purpose 9 channels

were added to the Thomson Scattering diagnostic at the TCV Tokamak (CRPP, Lausanne)

using polychromators developed for the RFX experiment in Padova and optimised for the

parameter range of interest. The additional channels were arranged to cover a region near the

plasma edge, on both sides of the last closed flux surface, with a spatial resolution of 1cm.

Due to flux expansion an even better resolution is obtained when the measurements are

mapped to the outer midplane. The system was used to study the evolution of electron

temperature and density profiles during the ELM cycle in quasi-stationary ohmic H-mode

phases with type-3 ELMs. As the laser emission cannot be synchronised with the ELMs and

the repetition rate of the Thomson scattering measurements is smaller than the ELM

frequency, the time evolution was obtained by random sampling, i.e. from profiles measured

at different phases within the ELM cycle. Each profile is mapped to the radial coordinate in

the equatorial plane using the reconstructed magnetic equilibrium and fitted by a modified

tanh function. This provides a measure of the pedestal height and the gradient scale length.

During most of the ELM cycle within a single shot the gradient lengths of Te and ne remain

almost constant. Immediately at an ELM event we observe a rapid decrease of the edge

density within ~100 µs followed by a slow recovery. This is interpreted as the result of an

outward flux of particles and energy associated with the ELM. The effect on the temperature

profile is much weaker or too fast to be resolved by the random sampling method. In a few

cases, when the measurements were taken < 100µs before the maximum of the ELM spike in

the D-α signal, we observed a clear ‘bump’ on the profiles outside the last closed flux surface.

These transient features are not yet fully understood, but show similarities to observations on

MAST.


Impurity behaviour and radiation pattern in the RFX- mod reversed field pinch

L. Carraro, A. Cravotta. E. Gazza, P. Franz, L. Marrelli, P. Martin, M.E. Puiatti, P. Scarin,

G. Spizzo, M. Valisa, B. Zaniol and the RFX team

Consorzio RFX, Associazione Euratom-ENEA sulla fusione

Corso Stati Uniti 4, 35127 Padova, Italy

RFX is the largest reversed field pinch operating nowadays, with 2 m in major radius, 0.459

m in minor radius and an installed power dimensioned to drive up to 2 MA of plasma current.

In the long shutdown period completed at the end of 2004, several new features have been

introduced. Above all, a closer resistive shell with externally fitted saddle coils has been

installed for better control of the axisymmetric plasma equilibrium and to try to harness the

rich spectrum of MHD modes. This paper describes the impact of the technical novelties of

the machine on the issues concerning the behaviour of the impurities, their production,

absolute content and spatial distribution in discharges with plasma current ranging between

300 and 600 kA.

In the former machine configuration, impurities did not represent a major problem. Despite

the strong plasma wall interactions the effective charge was kept at reasonable levels (i.e.

below 2), especially at high density. In this respect first observations on the restarted machine

confirm the trend. However a number of questions were kept pending; above all the effect on

the plasma performance of the strong poloidal and toroidal asymmetries in the emitted

radiation associated with the axisymmetric shift and the wall-mode locking. New insight on

those issues is given by the bolometer system that complemented by an extra camera on the

equatorial plane now allows the tomographic reconstruction of the radiation emission. There

is a specific interest in understanding the detailed shape and the radial extension of the

radiative layer in correspondence of localized plasma wall interaction, especially for density

values close to the Greenwald limit, and in general as a function of the MHD spectrum. The

analysis will be integrated by the spectroscopic observations interpreted by 1D impurity

transport codes.

The paper will describe also the effect of the new tiles of the all-graphite wall, which are

shaped in the poloidal direction, with a minimum interspace left between adjacent tiles, to

minimize the possibility of hot spots. Indeed the CCD camera observations confirm that the

wetted area is now reduced and the plasma wall interaction in the region of the wall–mode

locking is more evenly distributed.


Material Migration Studies at JET Using Tracer Techniques

M.J. Rubel1, J.P. Coad

2, J. Likonen

3, G.F. Matthews

2, D. Hole

4, E. Vainonen-Ahlgren

3 and

JET-EFDA contributors

1Alfvén Laboratory, KTH, Association EURATOM – VR, SE-100 44 Stockholm, Sweden

2Culham Science Centre, EURATOM-UKAEA Fusion Association, Oxon OX14 3DB, UK

3Association EURATOM-TEKES, VTT Processes, 02044 VTT, Espoo, Finland

4Accelerator Laboratory, University of Sussex, BN1 9QH Brighton, United Kingdom

Material migration studies by means of tracer techniques are essential to the assessment of

erosion, re-deposition and tritium retention in controlled fusion devices. An important issue

at JET is to understand the transport of carbon and its co-deposition with fuel species in

shadowed areas of the inner divertor. One way in which this is being done is via 13CH4

injection experiments performed at the end of campaigns preceding major shut-downs.

This contribution provides an overview of the latest tracer injection experiment

performed at JET in 2004 on the last operation day with the MkII-SRP divertor. Two tracers

were introduced by toroidally symmetric gas injection during 32 ELMing H-mode

discharges with strike points on the vertical target: 13CH4 from the outer vertical target and

tri-methyl borine (TBM) from the outer divertor base (private flux region). In addition,

hafnium was laser ablated from a single location on the outer midplane. The experiment was

followed by retrieval of several limiter and divertor tiles for ex-situ examination. Samples

have also been analysed from a specially designed fast reciprocating collector probe

introduced in each discharge from the top, low-field side of the poloidal cross-section.

The essential early results may be summarised by the following: (i) deposition of 13C on

the probe is non-uniform with the tracer being found predominantly on the side magnetically

connected to the outer divertor; (ii) a significant amount of 13C is deposited on the plasma

facing-surface of the inner divertor base tile. These two results indicate that material can

indeed be transported from the outer to inner divertor following a pathway through the

scrape-off plasma. There is no indication of the tracer migration to the inner divertor

shadowed region, thus supporting the current idea that carbon transport to that area is a

multi-step process and that there is no immediate C-D film formation in the shadowed region

during operation with strike points on the vertical targets. These results will be discussed in

terms of processes governing the material migration under divertor plasma conditions. The

possible role of ELMs on the erosion and re-distribution of deposited material will also be

addressed along with a comparison of results from the previous tracer experiment at JET.


Comparative Modeling of Type I ELM control by stochastic fields in

DIII-D, JET and ITER. M. Becoulet(1), E. Nardon(1), P. R. Thomas(1), G. Huysmans(1), J. F. Artaud(1), M. Lipa(1) , P.

Ghendrih(1), A. Grosman(1), R.A. Moyer(2), T.E. Evans(3), V. Chuyanov(4), G. Federici(4).

1 Association Euratom-CEA, CEA Cadarache, F-13108 St. Paul-lez-Durance, France. 2University of California, San Diego, La Jolla CA 92093, U.S.A.

3General Atomics, P.O. Box 85608, San Diego CA 92186-5688, U.S.A. 4ITER JWS Garching Co-center, Boltzmannstrasse2, 85748 Garching, Germany.

The recent successful experiments on Type I ELM control in DIII-D using stochastic

boundary represents a great interest for next-step tokamak ITER. The demonstration of high

confinement H-mode regimes without ELMs using stochastic boundary motivates the present

paper. Numerical results of heat transport modeling in the presence of Type I ELMs and

radial magnetic perturbation from external coils are presented for typical standard H-mode

scenarios for JET and ITER, and compared to the DIII-D modeling and experimental results.

Possible designs of the external coils for JET and ITER are analyzed taking into account

technical constrains for the possible implantation of such coils in JET and ITER and

optimization of the magnetic perturbation spectrum. The optimum magnetic perturbation

should be resonant mainly at the plasma edge in the pedestal region but not perturb the

plasma center where the addition error fields could lead to possible destabilization of

neoclassical tearing modes (NTM). The numerical simulations for each machine include two

steps. In the first stage 3D magnetic field calculations for the realistic set of external coils and

their spectrum are done for typical equilibrium of the standard H-mode scenario. A number of

possible designs for JET and ITER ergodic coils and corresponding spectrum in flux

coordinates are analyzed in a realistic geometry, with a goal to combine technical design

restrictions and the optimum perturbation spectrum. Then, the transport simulations are based

on the ideal linear MHD stability code MISHKA coupled with nonlinear energy transport 2D

code TELM. The main mechanism of the ELM crash in the code TELM is the increased

parallel conductive flux in the perpendicular to the magnetic surface direction caused by the

radial perturbation of the magnetic field due to the unstable ballooning mode. In the presence

of the external radial magnetic perturbation, the perpendicular transport is also increased in

the stochastic layer. The radial magnetic perturbation due to the ergodic coils can be

optimized to keep pedestal pressure gradient just under critical value for ballooning modes

value leading to ELMs suppression.


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Influence of toroidal field direction and plasma rotation on pedestal and

ELM characteristics in JET ELMy H-modes

A. Loarte1, G. Saibene

1, R. Sartori

1, M. Kempenaars

2, R.A. Pitts

3, Y. Andrew

4,

J.S. Lönnroth5, V. Parail

4, E. de la Luna

6, S. Jachmich

7, C. Giroud

4, M.F. Nave

8, K. Crombe

9

and contributors to the EFDA-JET workprogramme 1EFDA CSU-Garching, Boltzmannstrasse. 2, D-85748 Garching bei München, Germany

2Association EURATOM-FOM, FOM Rijnhuizen, P.O. Box 1207, 3430 BE, Netherlands

3CRPP-EPFL, Association Euratom-Confédération Suisse, CH-1015 Lausanne, Switzerland

4EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB,UK

5Association EURATOM-Tekes, Helsinki University of Technology, 02015 HUT, Finland

6Asociación EURATOM-CIEMAT, Avda. Complutense n. 22, E-28040 Madrid, Spain

7LPP, ERM/KMS, Association Euratom-Belgian State, B-1000, Brussels, Belgium

8Centro de Fusão Nuclear, Associaçao EURATOM-IST, 1096 Lisboa Codex, Portugal

9Department of Applied Physics, Ghent University, Belgium

Experiments have been carried out in JET to determine the influence of the toroidal

field (and plasma rotation) direction on the pedestal and ELM characteristics and on the

operational space of ELMy H-modes within the following ranges: plasma current Ip = 1.2-

3.0MA (with q95 = 3-3.6), additional heating (NBI and NBI +ICRH, dominated by NBI) Pin

= 9 – 17 MW and with various levels of gas fuelling. Due to the optimisation of the JET

divertor target for power handling, the helicity of the plasma must be preserved and, thus, Ip

and Bt were changed at the same time. Therefore, Forward Bt discharges (FB) had NBI co-

injection (toroidal co-rotation) while Reversed Bt discharges (RB) had NBI counter-injection

(toroidal counter-rotation).

The experiments show that pedestal and ELM characteristics are similar for both

directions of Bt, for discharges with similar levels of injected power. The pedestal pressure

of RB discharges is typically ~ 10-20% lower than that of discharges with the same level of

injected power (NBI+ICRH), in agreement with the steeper pedestal gradients measured for

RB discharges. ELM energy losses and ELM frequency are similar in FB/RB matched pairs,

indicating that the direction of Bt (and plasma co/counter-rotation) plays only a minor role in

determining them. Despite this, the direction of Bt (or of plasma rotation) has a clear

influence on the power and pedestal temperatures required to access the Type I ELMy H-

mode from Type III ELMs, which are typically ~ 30% higher and consistent with the higher

pedestal temperature for this transition (Type I å Type III) in RB discharges. Thus, the

maximum density achievable in Type I ELMy H-mode is ~ 10-20% lower in RB discharges.

Despite this, the maximum density achievable in H-mode (i.e., including Type III ELMs) is

similar for both directions of Bt .

The correlations between the measured pedestal plasma parameters and the divertor

characteristics in-between and during ELMs will be presented in the paper. The measured

edge/pedestal profiles will be compared with MHD stability codes and conclusions will be

extracted.


Tritium pathways in JET trace tritium transport experimentsJ. Hogan1, D. Hillis1, K-D. Zastrow2, M. Stamp2, P. Belo2, V. Parail2, G Corrigan2, D C

McDonald2, J. Spence2 and contributors to the EFDA-JET Work Programme1 Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

2 EURATOM / UKAEA Fusion Association, Culham Science Centre, Abingdon OX14 3DB, UK3 EURATOM/ I ST Fusion Association, Centro de Fusao Nuclear, Lisbon Portugal

Recent JET experiments have utilized transient puffed injection of low levels oftritium (< 1%), combined with detailed analysis of the time- and space-dependent response ofsubsequent neutron emission, to study the ρ*, ν* and β scaling of core particle transport inITB, ELMy H-mode and hybrid scenarios [1]. These trace T experiments also giveinformation which could help to characterize the pathways of the injected T and the influenceof the SOL on core transport. We present an analysis using available data for the pedestal /SOL region for three representative cases from the trace T experiments database. The casesconsidered, all with NBI only, exhibit a variety of ELM types: isolated, compound and small-scale 'grassy' ELMs. ELM expulsion is a sensitive process for edge particle transport soanalysis of this region requires an explicit, interpretive ELM model, previously developed[2]. Using the net radial influx of T+ ions at the edge of the core region (ρ=0.8) given byanalysis of neutron emissivity, the observed Tα behavior to set the ELM frequency andamplitude, and the measured T2 gas puff, we have calculated explicit ELM effects on inferrededge/pedestal D, V and also the response of recycled T flux at the walls / divertor, driven byELM behavior. Using the JET PTE1/DTE, Moeller-Scherzer, Grisolia et al and Wamplerrecycling saturation models [see 2], the resultant predicted maximum T recycling coefficientis found to vary strongly (0.01- 0.5) between the models, and with it the predicted ionfuelling contribution to pedestal T density. Edge/pedestal particle transport is stronglyinfluenced by ELM behavior: when explicit ELM effects replace ELM-averaged values, theturbulent (excess over neo-classical) diffusivities which match the transient in this region(ρ>0.8) are reduced by a factor 2-4 for the isolated / compound ELM cases (0.2 / 0.6 m2s-1

reduced to 0.05 / 0.2 m2s-1, respectively) and by 5 fold for the grassy ELM case (2.5 to 0.5m2 s-1). [1] K-D Zastrow et al, Plas. Phys. Cont. Fus. 46 (2004) B255 [2] P Andrew et al J Nucl Mater 266 (1999) 153; D Hillis et al Phys Plas 6 (1999) 1985

This work has been carried out under the European Fusion Development Agreement and was sponsored in partby the Office of Fusion Energy Sciences, U.S. Department of Energy.


Ripple-Induced Fast Ion and Thermal Ion Losses

T.P. Kiviniemi1, V.Parail2, T.Johnson3, J.Lönnroth1, T.Kurki-Suonio1, V.Hynönen1,J.Heikkinen4, S.Sipilä1 and contributors to the EFDA-JET workprogramme∗

1Association Euratom-Tekes, Helsinki University of Technology, FIN–02015 HUT, Finland2EURATOM/UKAEA Fusion Association, Oxfordshire, United Kingdom

3Association EURATOM-VR, Royal Institute of Technology, Stockholm, Sweden4Association Euratom-Tekes, VTT Processes, FIN–02044, VTT, Finland

In high performance plasmas the fast ion losses are considered as one of major contributorsto the loads on material surfaces. The ripple-induced losses may significantly enhance theseloads. This has been analyzed on JET using the Monte Carlo orbit-following code ASCOT [1]but, since the level of ripple in normal operation is low in JET (δ ≤ 2×10−3), the effect wasfound to be insignificant. However, JET has the unique possibility of controlling the strengthof the toroidal ripple, and experiments with varying ripple strength would certainly shed morelight on the confinement of ions trapped in local magnetic mirrors. Thus, it is of interest torepeat the ASCOT simulation with enhanced level of ripple. Also, ripple-induced transport asa tool for ELM mitigation is currently under investigation [2] and ASCOT simulations can beused to constract a reliable model for this transport for the transport code JETTO.

For the ripple field, a JET-based code which calculates the toroidal magnetic field configura-tion in JET (in R, Z andφ coordinates) for different current levels in the two sets of 16 toroidalcoils, with the two sets shifted byπ/16 in toroidal direction is used in the simulations. Aninterface to this data is programmed into ASCOT to upgrade the model to 3D. With the newmodel, a much more realistic estimate for the ion losses is computed by ASCOT to show thelevel and localisation of the losses as a function of the ripple amplitude, plasma parameters andthe magnetic configuration. Different methods to evaluateχi values from Monte Carlo simula-tion are discussed and compared with analytic theory [3]. First,χi is measured from variancegrowth of initially radially localized particle ensemble. Whenδ ≈ 10−2, χi already exceedsneoclassical value significantly. Second, closer to the edge, estimate forχi is evaluated fromthe number of lost particles and it is studied if the loss process is diffusive at all. Third methodis to initialize the particle ensemble according to experimental density and temperature pro-files, follow them in the presence of momentum and energy conserving binary collisions andestimateχi from heat flux measured from particle ensemble [4].

References[1] T.Kurki-Suonioet al, Nucl. Fusion42 (2002) 725

[2] V. Parail et al, "Effect of Ripple-Induced Ion Thermal Transport on H-mode Perfor-mance", this conference

[3] P.N. Yushmamanov, Rev Plasma Phys. v. 16, New York, Consultant Bureau (1991)

[4] T.P. Kiviniemi et al, Contrib. Plasma Physics42 (2002) 236

∗See the Appendix of J.Pamela et al., Fusion Energy 2004 (Proc. 20th Int. Conf. Vilamoura, 2004) IAEA,Vienna (2004)


In situ measurement of chemical erosion yields

for the production of C2Hy in the JET outer divertor

S.Brezinsek1, M.F.Stamp2, A.Pospieszczyk1, A.Meigs2, A.Huber2, S.Droste1

A.Kirschner1, Ph.Mertens1, S.Jachmich3, V.Philipps1, G.F.Matthews2

U.Samm1 and contributors to the EFDA-JET workprogramme*

1Institut fur Plasmaphysik, Forschungszentrum Julich GmbH, EURATOM-Association,Trilateral Euregio Cluster, D-52425 Julich, Germany

2EURATOM/UKAEA Fusion Association, Culham Science Centre, Oxon OX14 3DB, UK3Laboratoire de Physique des Plasmas/Laboratorium voor Plasmafysica, ERM/KMS,

EURATOM Association, Trilateral Euregio Cluster, B-1000 Brussels, Belgium

Graphite is currently planned for the high heat load areas of the ITER divertor targets.

Erosion will determine both the lifetime of these components and the long term retention

of tritium via the formation of hydrogen-rich carbon layers on remote areas and on the

targets themselves. A reliable database exists for the chemical erosion yield of graphite

under impact of energetic and thermal hydrogen in beam experiments, but although data

describing the erosion behaviour of graphite targets in fusion devices have recently been

compiled and critically revisited [Roth et al. 2004], the situation remains uncertain with

respect to the role played by higher hydrocarbons in determining the total erosion yield.

In JET, experiments in high-clearance L-mode discharges (H fuel, 2.43 T, 2.5MA, 3.4 MW

NBI) have been performed in an attempt to spectroscopically determine the (molecular)

carbon flux originating from chemical erosion resulting in species C2Hy. The approach

is to introduce ethene into the divertor plasma through gas injection modules positioned

circumferentially in the horizontal and vertical target plates. This allows the in situ

calibration of spectroscopic photon fluxes emitted by hydrocarbon fragments along the

dissociation chain. Reference discharges with hydrogen injection have been performed in

order to match the plasma edge parameters which are perturbed as a result of the hydro-

carbon injection. A slow strike point sweep from horizontal to vertical targets places the

injection location sequentially into the private flux region, separatrix or scrape-off layer.

The plasma parameters at the injection location thus vary during the sweep, reaching max-

imum values of Te = 14eV and ne = 7.5*1019m

−3 with peak ion fluxes of 3*1024s−1

m−2.

The increase in measured photon fluxes due to the hydrocarbon species C2(Swan band),

CH(Gero band), CI(909nm), CII(427nm/514nm), CIII(465nm) with respect to the ref-

erence discharges can be attributed to the injected C2H4. Effective photon efficiencies

are estimated from the ratio between photon and particle fluxes and then applied to the

intrinsic photon fluxes. The final step is to relate the intrinsic C2Hy fluxes to the incident

hydrogen flux and thus provide the chemical erosion yield for C2Hy. This contribution

will report on the measured yields –the upper limit of which has been determined to be

below 2%– and will compare the experimental findings with ERO-JET simulations using

EDGE2D-NIMBUS background plasmas for three dedicated strike-point positions.*See the Appendix of J.Pamela et al., Fusion Energy 2004 (Proc. 20th Int. Conf. Vilamoura, 2004) IAEA, Vienna (2004)


0ROHFXODU+'7VRXUFHVLQ-(7

A.Pospieszczyk2, S.Brezinsek2, A.Meigs1,G.Sergienko2, M.Stamp1

and JET-EFDA contributors

8.$($(XUDWRP)XVLRQ$VVRF&XOKDP6FLHQFH&HQWUH$ELQJGRQ2[RQ2;'%8.,QVWLWXWIU3ODVPDSK\VLN)RUVFKXQJV]HQWUXP-OLFK*PE+(85$720$VVRFLDWLRQ7ULODWHUDO

(XUHJLR&OXVWHU'-OLFK*HUPDQ\ Both tritium and deuterium will be used in equal measure as fuel species in future fusion reactors. A

number of separate experiments have been conducted at JET over the years in which tritium has been

introduced in various quantities relative to the deuterium content, the most recent of which was the

“trace tritium” campaign, in which tritium has been puffed both from the wall and injected via the

neutral beam heating line. The quantity of injected tritium was maintained at very low levels (less than

1%) in order to keep the radiation level low and decontamination time of the vessel short. Since gas

puffed tritium is introduced as a molecule via the nozzle and recycles mainly in the form of hydrogen

isotopomeres, it is of interest to investigate the formation, particularly of DT molecules, with regard to

the total fuelling of T achieved in the discharge. This contribution describes the use of molecular

spectroscopy, employed in a similar way to that reported in [1], to investigate DT molecule formation

for the first time in JET.

The Fulcher- spectrum of both H2 (introduced for test measurements and calibration

purposes), and T2 has been clearly identified at the location of the gas puff. This tritium data, obtained

under fusion edge plasma conditions, will be compared with laboratory molecular T2 spectra published

more than 50 years ago and produced under very different discharge conditions [2]. Measurements will

also be reported for the formation of DT-molecules in the JET outer divertor volume. Here, although

HD-molecules can easily be detected and discriminated from the D2-molecular background in the case

of specific H2 blow experiments, the detection of DT-molecules in the T2-blow case is marginal, very

probably due to the much lower amount of injected T2. Using the law of mass action it can be shown

that the detection of the isotopomeres DH and DT is a very sensitive means by which to measure low

quantities of H2 or T2 respectively. A similar, but not so sensitive approach has been performed in [3]

using tritiated hydrocarbon radicals. In the hydrogen case, the HD fraction was about 10% of the

molecular D2 flux, resulting in a 1% contribution of H2 to the D2 flux. Since the puffed tritium in these

recent JET shots was about one order of magnitude smaller than the H flux introduced during the

calibration experiments, a DT-flux of only ~1% is expected, resulting in a T2 flux of 0.1% . Evidence

will be presented that similar levels have indeed been detected, although the signals were near the

detection limit, demonstrating that this type of spectroscopy offers an interesting potential tool as a

fuelling and recycling rate diagnostic.

[1] A.Pospieszczyk, S.Brezinsek , G.Sergienko et al, to be publ. in J.Nucl.Mater. (2005)

[2] G.H.Dieke and F.S.Tomkins, Phys.Rev. 76 (1949) 283

[3] G.Duxbury, M.G.O’Mullane, H.P.Summers et al, VW(36&33/RQGRQ(&$9RO*3


Applying Advanced Statistical Techniques to Tokamak L-H Threshold Data

A.J.Meakins 1 , D.C.McDonald

2 , Y.Andrew

2, J.G.Cordey

2, M.Coppins

1,

ITPA H-mode Threshold Database WG 3 and contributors to EFDA JET workprogramme

*

Work partly funded by Euratom and the UK EPSRC

1. Imperial College, Prince Consort Road, London, SW7 2BZ, UK

2. EURATOM-UKAEA Fusion Association, Culham Science Centre, Abingdon, UK

3. Alcator C-Mod: J.A.Snipes, M.Greenwald; ASDEX/ASDEX Upgrade: F.Ryter,

O.J.W.F.Kardaun, J.Stober; COMPASS-D/MAST: M.Valovic; DIII-D: J.C.DeBoo;

JET/EFDA: Y.Andrew, J.G.Cordey, R.Satori, K.Thomsen; JFT-2M/JT-60U: T.Takizuka,

Y.Miura, T.Fukuda, Y.Kamada, K.Shinohara, K.Tsuzuki; PBX-M/NSTX: S.M.Kaye,

C.Bush, R.Maingi; TCV: Y.R.Martin; TUMAN-3M: S.Lebedev.

* See the Appendix of J.Pamela et al., Fusion Energy 2004 (Proc. 20th Int. Conf.

Vilamoura, 2004) IAEA, Vienna (2004)

When planning experiments on a given tokamak empirical log-linear power law fits are often

used to predict parameters by interpolating data from past experiments. Predicting the

threshold heating power required to achieve a transition from the L-mode to the H-mode of

operation is one such area where these scalings are used frequently. The JET L-H threshold

data, however, is known to contain regions of operating space (e.g. at low density) where

power law fits are unsuitable. In this paper we present a Neural Network (NN) approach to

the analysis of JET L-H data. NNs have a more flexible functional form allowing them to

describe more complex trends in the data. Fitting the NNs is performed using a novel code,

DyNE, which explicitly prevents overfitting of the data. Results show an improvement in

predictive ability compared to power laws fit to the same data (13% improvement in Root

Mean Squared Error) and features such as the low density behaviour of the L-H threshold are

correctly described. The application of this method to next step devices, such as ITER, would

provide a useful tool that should allow for significant savings in experimental time.

As it is not possible to extrapolate from NNs, extrapolation of L-H threshold data to next step

devices power law scalings remain the more appropriate tool. The majority of power law

scalings used in multi-machine comparisons are fit using Ordinary Least Squares (OLS). A

key assumption in the derivation and application of OLS is that any random scatter in the

data must be present only on the dependent variable otherwise the fits become biased. If

errors on the data do not agree with this assumption then more sophisticated fitting

techniques must be applied. We present an analysis of the errors in the International Global

H-mode Threshold Database (IGDBTH) which shows that the errors on the dependent and

independent variables are comparable. As such we apply Errors-in-Variables Orthogonal

Regression (EVOR) which treats the errors in the dependent and independent variables in an

equal manner. For the IGDBTH the errors in one of the independent variables was found to

be of similar magnitude to the dependent variable suggesting a skewed OLS fit. Refitting

using EVOR produced a modified scaling. This scaling predicts the threshold power for

ITER to be 37-38MW, a small increase of 3-4MW over previous estimates, however it still

falls within the ITER design parameters.


ELM-limiter interaction on JET

W.Fundamenski1, P.Andrew1, A.Boboc1, G.F.Matthews1, J.Paley3, L.Pickworth1, R.A.Pitts2, V.Riccardo1 and contributors to the EFDA JET workprogramme*

1Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK

2CRPP, Assoc. Euratom-CSEPFL, CH-1015, Lausanne, Switzerland 3Imperial College, London, SW7 2B2, UK

The interaction of edge localized modes (ELMs) with the tokamak first wall (divertor and limiter

tiles) is one of the critical issues for ITER. While parallel transport of ELM energy to the divertor has

been extensively studied, radial transport to the limiters is still poorly characterised. There is now

ample evidence of the filamentary structure of ELMs, with a toroidal mode number ~ O(10) in

agreement with the prediction of the peeling-ballooning model. On JET, ELM filaments are observed

to propagate outwards at average velocities of 0.4 – 0.75 km/s, while the filament ne and Te decay

radially with average e-folding lengths of λn ~ 12 cm and λTe ~ 3 cm, mapped to the outer mid-plane.

The key issue is the decay of the ion temperature, Ti, and hence of the total energy density,

~3/2×(neTe + niTi) in the ELM filament.

Dedicated experiments designed to measure the radial profiles of the total energy density of

Type-I ELM filaments have been performed on JET (2.5 MA/2.4 T, 12 MW NBI, fELM ~ 20-30 Hz,

∆W/Wped ~ 3-5 %). In the absence of a main chamber infra-red (IR) system, to be installed on JET in

2005, an indirect method was adopted. The outer wall gap was slowly reduced in the course of the

discharge, while the outer divertor strike point was held fixed at the optimal viewing location for the

divertor IR camera. By examining the change in deposited power on the outer divertor, while

monitoring the fractional drop in the pedestal stored energy, the effective power profile of an average

Type-I ELM filament was inferred as λTiELM ~ 8 ± 3 cm such that λTi / λTe ~ O(3). This implies that

ions in the ELM filament are cooled much slower than electrons, consistent with lower ion parallel

mobility. The evolution of both temperatures agrees well with the predictions of a 1-D fluid-kinetic

model in the frame of reference moving with the ELM filament. The above conclusions include two

main uncertainties: the effect of outer wall gap on the size of the ELMs and IR data interpretation.

The methodology of overcoming these problems will be described systematically.

Finally, indirect evidence of ELM-limiter interaction is provided by mechanical sensors

which indicate transient displacements (<50 µm) of the JET vacuum vessel with respect to its

external supports. These displacements, which increase with ELM size and are largest for the

smallest outer wall gap, are associated with plasma current loss to the limiters during the ELM,

which leads to a change in plasma equilibrium and a reaction by the vertical stabilisation system.

This work was conducted under EFDA and was partly funded by Euratom and the UK EPSRC. *See the Appendix of J.Pamela et al., Fusion Energy 2004 (Proc. 20th Int. Conf. Vilamoura, 2004) IAEA, Vienna (2004).


Gas Jets and Their Interaction With Magnetically Confined Plasmas*

G.Y. Antar1 and T.C. Jernigan2

1University of California – San Diego, La Jolla, California, USA2Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA

Gas jets are used in tokamak plasmas for multiple purposes. Lately, high-pressure gas jetswere successfully used for disruption mitigation in the DIII-D tokamak [1]. This isparticularly important for next step devices such as ITER. We report studies of the gas jetdynamics in vacuum inspired by what is known in gas dynamics. Also the dynamics of gasflow in ducts is presented. We emphasize the fact that the dynamics of gases in vacuumand ducts can be expressed in rather simple analytical formulas. In order to study the gas jetinteraction with the plasma, numerical simulation is used with the DIII-D conditions for boththe plasma and the gas jet setup. We include only electrons interaction with the gas neutrals,solving the particle and energy balance equations with 5×10-9 s temporal resolution and 5 mmspatial resolution in both radial and toroidal directions. The result of the simulations indicatesthat the jet penetration is small for the different types of gases used. The next step for gas jetsimulation should include the different ionization levels of impurity ions, a more realistictreatment of the parallel and radial transport phenomena.

[1] D.G. Whyte, et al., Phys. Rev. Lett. 89, 055001 (2002).

*Work supported by the U.S. Department of Energy under DE-FG02-04ER54758 and DE-AC05-00OR22725.


Divertor particle and power deposition profiles

in JET ELMy H-mode discharges

S. Jachmich1, T. Eich2, W. Fundamenski3, A. Kallenbach2, R. A. Pitts4 and contr. EFDA-JET workprogramme+

1 Laboratory for Plasmaphysics, Ecole Royale Militaire/Koninklijke Militaire School, EURATOM-Association “Belgian State”, Brussels, Belgium, Partners in the Trilateral Euregio Cluster (TEC)

2 Max-Planck Institut fuer Plasmaphysik, Euratom Association, Garching, Germany 3 EURATOM-UKAEA Fusion Association, Culham Science Centre, United Kingdom 4 Centre de Recherches en Physique des Plasmas, Association EURATOM, Conférédation Suisse,

EPFL, 1015 Lausanne, Switzerland

Characterising the transient pulses of heat and particles arriving at the divertor target plates

as a consequence of upstream ELM activity is an important aspect of research on current

tokamaks with respect to scaling for ITER. Such efforts require measurement of the ELM

time behaviour with both high temporal and spatial resolution. On JET this has been

achieved by slowly sweeping the divertor strike points of ELMing H-mode discharges over

an array of target embedded Langmuir probes in the MarkIISRP divertor. By measuring the

probe currents for different probe operation modes, ELM and inter-ELM particle flux and

temperature profiles are obtained using coherent averaging techniques. To study the effect of

pedestal collisionality and classical drifts on Type-I and -III ELM fluxes, experiments were

performed with varying heating power, plasma density and magnetic field direction.

The key result is the observation of target particle flux profile broadening with

respect to the inter-ELM level during Type-I ELMs. At the ELM peak, the profile remains

exponential, with an e-folding length twice that of the inter-ELM value, presumably as a

consequence of the enhanced radial transport. This behaviour should be compared to earlier

infra-red power profile observations (in the JET MarkIIGB divertor) where little or no

broadening was observed during Type-I ELMs. Detailed comparisons of the infra-red and

Langmuir probe power deposition profiles obtained during the more recent experiments will

be presented. The methodology of calculating the theoretically predicted [1,2] transient

changes in the sheath heat transmission coefficients will be outlined.

The second important result consists in the observation that whilst the magnetic field

direction has little effect on the particle flux profile during Type-I ELMs, it significantly

affects Type-III ELM profiles: reversing the magnetic field (B×∇B direction away from the

X-point) leads to narrower profiles. This finding provides valuable information on the ELM

crash dynamics for these two types of ELMs. Finally, the observation of strong target

currents during ELMs, which coincide with the rise in divertor Dα emission, will also be

discussed.

[1] W. Fundamenski, to be submitted to Plasm. Phys. Contr. Fus. [2] D. Tskhakaya, J. Nucl. Mat. 313-316 (2003), 1119. + see appendix of J. Pamela, Fusion Energy 2004 (Proc. 20th Int. Conf. Vilamoura, 2004) IAEA, Vienna (2004).


Fractal growth of dust and globular films in T-10 tokamak.

L.N. Khimchenko1, V.P.Budaev

1, M.I.Guseva

1, B.N.Kolbasov

1,

B.A.Loginov2, O.N.Makeev

2, A.L.Suvorov

2

1RRC "Kurchatov Institute", Moscow, Russia2Institute for Theoretical and Experimental Physics, Moscow, Russia

Tritium retention in the deposited films is one of the critical issue related to the safety

hazard in large fusion device such as ITER. The presence of micrometer-sized dust

particles transported from the wall into the edge plasma can seriously alter the plasma

property and performance of large fusion devices.

A lot of films and dust samples found in the T-10 tokamak exhibit fractal structure

of surface organized in hierarchical way of structures like globe-shape and cauliflower-

shape [1]. Dust particles have typically three hierarchical levels of agglomeration in the

range of dimensions from ~20 nm to ~2 om. The surface of globular films has typically

five hierarchical levels of stratified dimensions from ~50 nm to ~50 om. Fractal dimension

of globular films (found of D \ 2.15 „ 2.32) indicates increased film’s sorption of gases

by stratified surface.

To describe fractal surface texture some of the carbon films observed in the T-10

tokamak, diffusion limited aggregation (DLA) model of fractal growth is used. It is stressed

the importance of non-Gaussian statistics of edge plasma turbulence that generates

cauliflower – shape of the deposited films. In the vicinity of the wall, non-Gaussian statistics

of electric field fluctuations drives not a standard Brownian motion (classic diffusion), rather

Levy - type diffusion (superdiffusion) of deposited particles. Main features of the films

observed in tokamaks, such as fractality of surface texture, globe-shape and a fivebranch

symmetry are exhibited in the computer simulation of the fractal growth.

Observed in the T-10 tokamak carbon films with fractal structure have increased

level of deuterium ( D/C \ 0.6 „ 0.8) [1]. Therefore fractal growth mechanism discussed in

this paper, may generate the increased sorption of tritium by co-deposited films and dust

particles in ITER.

[1] L.N.Khimchenko et al., Proc. 31th

EPS Conf. on Plasma Physics, London (UK), June 28 -

July 2, 2004 , P-4.147


Impact of Magnetic Configuration on Edge Radial Electric Field:

MAST-ASDEX Upgrade Simulation with B2SOLPS5.0

V. Rozhansky1, E. Kaveeva1, S. Voskoboynikov1, G. Counsell2, A. Kirk2, H. Meyer2,

D. Coster3, G. Conway3, J. Schirmer3, R. Schneider4 and the ASDEX Upgrade Team

1St.Petersburg State Polytechnical University, Polytechnicheskaya 29, 195251 St.Petersburg, Russia2EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK

3Max-Planck Institut für Plasmaphysik, EURATOM Association, D-85748 Garching, Germany4Max-Planck Institut für Plasmaphysik, EURATOM Association, D-17491 Greifswald, Germany

A detailed modeling of the radial electric field in the separatrix vicinity has been

performed for three divertor configurations: Upper Double Null (UDND), Lower

Double Null (LDND) and Connected Double Null (CDN). Ohmic shots from MAST

and AUG were chosen for simulation. In MAST the radial electric field at the LFS

equatorial mid-plane was more negative in CDN case than for LDND case and was

similar to that in UDND case. A strong steady state negative spike of the electric field

was obtained for CDN case at HFS equatorial mid-plane. Toroidal rotation at the LFS

for MAST is less negative for CDN than for LDND case as in the experiment and is

similar to UDND case. For the AUG simulations the LFS radial electric field in the

CDN case was more negative than that for LDND. The UDND electric field was

significantly less negative than the radial fields in the two other cases. Simulation

results are consistent with radial electric field measurements on AUG. As in the

MAST case, a negative spike of the HFS radial electric was also obtained for CDN.

The toroidal rotation was more negative in LDND case and less negative in UDND

case than in CDN. The physical mechanism responsible for the change of the radial

electric field in various configurations is connected with toroidal rotation transported

from the SOL through separatrix to the core region. The results obtained might

contribute to the understanding of the experimentally observed easier access to the H-

mode in the CDN configuration.

Acknowledgements This work was funded partly by the United Kingdom

Engineering and Physical Sciences Research Council and by EURATOM.


Investigation of the plasma potential behaviour at the edge of the T-10

tokamak by HIBP

L.G. Eliseev1, A.V. Melnikov1, A.V. Gudozhnik1, S.E. Lysenko1, V.A. Mavrin1,

S.V. Perfilov1, V.A. Vershkov1, L.I. Krupnik 2 1 Nuclear Fusion Institute, RRC "Kurchatov Institute", 123182, Moscow, Russia,

2 Institute of plasma physics, NSC “Kharkov Institute of Physics and Technology”,

Kharkov, Ukraine

The plasma potential was investigated by Heavy Ion Beam Probing (HIBP) at the outer

edge of the T-10 tokamak (R = 1.5 m, a = 0.3 m, B0 = 2.4 T) within the radial interval of

25-30 cm. The plasma was limited by the movable rail limiter at alim = 27 – 30 cm, and the

circular limiter at ac lim = 33 cm. The plasma potential profile was measured along with the

probing beam current, representing the density profile.

In the Ohmic phase of the deuterium discharge (Ip = 180 kA, ne = 1.5×10 19 m-3) the

negative plasma potential was observed. The slope of the potential profile gives the

estimation of the mean radial electric field in a range of Er = - 50 – 100 V/cm.

In the ECRH phase with on- and off- axis power deposition (PEC = 1- 1.2 MW,

rECRH = 0, -13 cm) the potential well becomes significantly swallower. The estimated mean

radial electric field was in a range of Er = -10 –30 V/cm.

In the Ohmic phase of the He discharge (Ip = 240 kA, ne = 2.5×1019 m-3) the

negative plasma potential was also observed with the similar range of Er. The insertion of

the rail limiter into alim = 27 cm leads to the modification of the plasma profiles. The radial

reference of the plasma potential profile was linked with the rail limiter position, but its

shape was the same. In the rail limiter shadow, 27 cm < r < 30 cm, the potential is close to

zero. The modifications of the density profiles were not so significant in the investigated

case.

The plasma potential evolution shows the link of the potential value with density.

During the C-pellet injection (Ip = 180 kA, ne = 1.5×10 19 m-3), the edge potential falls

down up to –100 V with the density rise. The mean value of the negative electric field

becomes stronger up to Er = –120 V/cm.

The work is supported by Federal Atomic Energy Agency of RF, and Grants RFBR

02-02-17727, NSh-1608.2003.2, INTAS 2001-2056 and NWO-RFBR 047.016.015.


Influence of flux surface shape on DALF and ITG edge turbulence

A. Kendl1, B.D. Scott2

1 Institut für Theoretische Physik, Universität Innsbruck, A-6020 Innsbruck, Austria2 Max-Planck-Institut für Plasmaphysik, EURATOM Assoc., D-85748 Garching, Germany

The influence of shaping of magnetic flux surfaces in tokamakson gyrofluid edge turbu-

lence is studied. Magnetic field structure in tokamaks is mainly due to elongation, triangularity,

pressure shift and the presence of a divertor X-point. A series of tokamak configurations with

varying elongation and triangularity, and an actual ASDEX Upgrade divertor configuration are

obtained with the equilibrium code HELENA and implemented into the gyrofluid turbulence

code GEM. Specific effects of flux surface shaping on drift-Alfven (DALF) and ion tempera-

ture gradient (ITG) turbulence in the tokamak edge plasma areanalysed and compared.


On the Interaction of a Rotating Magnetic Field with the Plasma inthe Kinetic Approximation∗

M. F. Heyn1, I. B. Ivanov2, S. V. Kasilov3, and W. Kernbichler1

1Institut fur Theoretische Physik, Technische Universitat Graz

Petersgasse 16, A–8010 Graz, Austria

2Petersburg Nuclear Physics Institute, 188300 Russia,

3Institute of Plasma Physics, National Science Center “Kharkov Institute of Physics

and Technology”, Ul. Akademicheskaya 1, 61108 Kharkov, Ukraine

The interaction of a rotating magnetic field with an inhomogeneous cylindrical plasma

is considered in the kinetic approximation. In the derivation of the the conductivity

operator a specific finite Larmor radius expansion is used such that on one hand the pos-

itive definiteness of the absorbed power is guaranteed for the homogeneous Maxwellian

plasma and on the other hand the correct electrostatic limit in the zero frequency limit

is obtained. The effects of a pressure gradient, namely an asymmetry of the power cou-

pling from the rotating field to the plasma with respect to the poloidal phase velocity

of the field are studied.

∗This work has been carried out within the Association EURATOM-OAW and with funding fromthe Austrian Science Foundation FWF contract P15956-N08.


Modelling of combined effect of TF r ipples and MHD per turbations on fast ion behaviour in tokamaks

K. Schoepf 1, V. Goloborod’ko

1,2, S. Reznik

1,2, V. Yavorskij

1,2

1Association EURATOM-OEAW, Institute for Theoretical Physics, University of Innsbruck,

Innsbruck, Austria 2Institute for Nuclear Research, Ukrainian Academy of Sciences, Kiev, Ukraine

Toroidal field (TF) ripples as well as MHD induced low frequency perturbations are

known to lead to an enhanced loss of fast ions in tokamaks due to the break down of toroidal

momentum conservation [1,2]. Usually, theoretical investigations of the effects of ripple and

MHD perturbations on fast particle confinement neglect the synergetic impact of these

perturbations. According to Ref. [3], however, TF ripples together with TAE modes may

result in a significant synergistic enhancement of fast ion loss in magnetically confined

toroidal plasmas. On TFTR it has been experimentally demonstrated [2] how MHD

perturbations modulate the loss of charged fusion products due to TF ripples; both

enhancement and reduction of fast ion loss was observed. The objective of the present study

is the modelling of the joint effect of toroidal field ripples and MHD-perturbations on the

transport behaviour of fast ions in a tokamak magnetic configuration. We carry out our

analysis in the single-harmonic approximation, in which each type of the perturbations is

represented by a single harmonic. The combined effect of both perturbations on the stochastic

domain in phase space is investigated by analysis of pair correlations of toroidal momentum

variations [4] calculated with the simplectic integration method for Hamiltonian systems [5].

MHD perturbations are shown to result potentially in both, either an enhancement or a

weakening of the fast ion diffusion coefficients observed in a MHD quiescent plasma.

References

[1] GOLDSTON, R.J., et al., Phys. Rev. Lett. 47, (1981) 647.

[2] ZWEBEN, S.J., et al., Nucl. Fusion 40, (2000) 91.

[3] HLADSCHIK, T. and SCHOEPF, K., Proc. Int. Conference on Plasma Physics, Foz

do Iguacu, Brazil, Oct/Nov 1994, Vol 1, pp. 29-32.

[4] CHIRIKOV, B.V., Sov. J. Plasma Phys. 4(3), (1978) 289.

[5] CHANNELL, P.J. and SCOVEL, C., Nonlinearity 3, (1990) 231.


Full f particle simulation of internal transport barrier formation

T.P. Kiviniemi1, J.A. Heikkinen2, S.V. Henriksson1 and S. Janhunen1

1Association Euratom-Tekes, Helsinki University of Technology, FIN–02015 HUT, Finland2Association Euratom-Tekes, VTT Processes, FIN–02044, VTT, Finland

Full f gyrokinetic particle simulation code ELMFIRE has been written for electrostatic tur-

bulent plasma simulation in tokamaks allowing significant changes in plasma profiles during

simulation. Applying the code in FT-2 tokamak configuration, the formation of internal trans-

port barrier (ITB) was found with sufficient lower hybrid ion heating in accordance with the

experimental observations of ion temperature profile and related transport coefficient inter-

pretation [1]. The ELMFIRE code has been benchmarked against the other gyrokinetic code

predictions for the Cyclone base case linear mode characteristics and nonlinear saturation level

of χi in both adiabatic and kinetic electron simulations [2]. Moreover, detailed predictions of

neoclassical properties, including the radial electric field, in the presence of turbulence have

been performed.

In the present work, the origin of the ITB formation in the FT-2 experiment is analysed in

greater detail using the ELMFIRE simulation. The relative roles of the Ware pinch, Oxygen

impurity effects on the turbulent modes, fast ion orbit losses, rotation shear by neoclassical

poloidal rotation and turbulence driven Reynolds stress, and recycling details on the trans-

port barrier generation are investigated for the rapidly evolving plasma pressure profile during

heating and transport collapse.

References

[1] J.A. Heikkinen, S.J. Janhunen, and T.P. Kiviniemi, EPS London, 2004 31st European

Physical Society Conference on Plasma Physics, 28 June - 2 July 2004, London, United

Kingdom. P-5.161.

[2] J.A. Heikkinen, S.J. Janhunen, and T.P. Kiviniemi, "Global full f gyrokinetic particle sim-

ulation of tokamak turbulence using direct implicit method", submitted for publication,

2005.


Characteristics of fluctuations in ELMFIRE simulations

S.V.Henriksson1, S. Janhunen1, T.P. Kiviniemi1, J.A. Heikkinen2 1 Association Euratom-Tekes, Helsinki University of Technology, Espoo, Finland 2 Association Euratom-Tekes, VTT Processes, Espoo, Finland

In a turbulent plasma there are fluctuations of various scales and amplitudes. In a typical

fusion device the relative fluctuation level changes by a decade from the reactor core to the

plasma edge. Characteristic properties of the fluctuations can be obtained by quantities that

allow the ensemble averaging procedure. In this work we consider spectra, correlation

functions and PDFs obtained from simulations of the FT-2 tokamak plasma performed with

the global full f gyrokinetic code ELMFIRE. Fluctuations under different conditions and in

different parts of the tokamak are investigated and the results are compared with analytic

theories and previous observations.

The power spectra peak near the most unstable drift mode, and follow Kolmogorov-type

power laws S(k)= Ck-α for larger wavenumbers. A variation of the exponent α with radius is

observed, suggesting that the relation and energy transfer between different scales depends on

local plasma conditions. Transport reduction in an internal transport barrier is seen to be

accompanied by a decrease in the amplitudes of small wavenumbers. A two-dimensional

cross-correlation function is used for determining the lifetime and poloidal size of

fluctuations. A decrease in fluctuation sizes in saturated turbulence is observed. The PDFs of

the fluctuations are fitted to Levy-type distributions. The Levy index varies with location,

once again implying that fluctuation characteristics are different in different parts of the

tokamak.

[1] J.A. Heikkinen, S.J. Janhunen, and T.P. Kiviniemi, “Gyrokinetic Simulation of

Neoclassical and Turbulent Transport”, 31 EPS conference on Plasma Physics, London 28.6-

2.7.2004

[2] P.Hennequin et. al., “Scaling laws of density fluctuations at high-k on Tore Supra”,

Plasma Phys. Control. Fusion 46 (2004) B121-B133


On magnetic fluctuations and parallel dynamics of drift wave turbulence

in the torsatron TJ-K

N. Mahdizadeh3), K. Rahbarnia3), F. Greiner3), T. Happel3), E. Holzhauer1),

M. Ramisch1), B. Scott2), U. Stroth1)

1) Institut für Plasmaforschung, University Stuttgart, Germany2) Max-Planck-Institut für Plasmaphysik, Garching, Germany

3) Institut für Experimentelle und Angewandte Physik, University Kiel, Germany

The torsatron TJ-K is operated with a low-temperature plasma with the objective to study tur-

bulent transport and wave propagation in a fusion-relevant magnetic configuration and with

excellent diagnostic access. Although the plasma parameters are much lower than in the fusion

edge plasma, the dimensionless parameters determining turbulence are similar.

In previous investigations it has been shown [1] that the turbulence in TJ-K is dominated

by drift waves. The cross phase between density and potential fluctuations was detected to

be close to zero on all spatial scales. On closed field lines this is a signature of a pressure

gradient parallel to the magnetic field. This key property of drift waves is now being investigated

by measurements of the parallel structure of density and potential fluctuations using an 8× 8

Langmuir probe matrix and a movable reference probe. Furthermore, the parallel electric current

driven by a parallel pressure gradient leads to a coupling of the turbulence to Alfvén waves and

hence to magnetic fluctuations.

This contribution will present first results on the 3-dimensional structure of the turbulence

in the core plasma of TJ-K. The magnetic field lines have been calculated and measured with

thermionic micro discharges. The turbulent structures exhibit a deviation from the field lines

and clear indications for a finite parallel wave length λ‖ are found. The dependence of λ‖ on

the ion sound speed and other parameters will be studied by operating the plasma with different

gases ranging from hydrogen to argon.

The magnetic fluctuations are measured by induction probes positioned inside the confine-

ment region of the plasma. Experimental spectra have been measured for the accessible plasma

parameter range and will be compared with results from the drift-Alfvén-wave code DALF3 [2]

and with density and potential fluctuation spectra.

References

[1] U. Stroth et al., Plasma Phys. 11, 2558 (2004).

[2] B. Scott, Plasma Phys. Controll. Fusion 39, 1635 (1997).


Impurity transport studies in TORE SUPRA with He-like spectroscopy

O. Marchuk1, G. Bertschinger1, C. Fenzi-Bonizec2, B. Shunke2, M. Mattioli2,

A. Whiteford3, N.R. Badnell3

1 Institute für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Association,

D-52425 Jülich, Germany∗

2 Association Euratom-CEA sur la Fusion Contrôlée, DSM/DRFC, CEA Cadarache,

13108 St. Paul-lez-Durance, Cedex, France3 Department of Physics, University of Strathclyde, Glasgow, G4 0NG, UK

X-ray spectroscopy is one of the most promising diagnostic to investigate hot core fusion plas-

mas. Core electron and ion temperatures as well as toroidal plasma velocity can be routinely

determined from He-like impurity spectra [1]. In addition,the He-like spectra contain infor-

mation on the relative abundance of the ionized species and so on the transport properties of

the plasma. Therefore, the He-like ion diagnostic can be used to understand the behavior of

the impurities in the plasma core.

The aim of this work is the experimental determination of thediffusion coefficients of iron

in the tokamak TORE SUPRA. Our approach is split into two parts. In the experimental part

we obtain the density of H-, He-, and Li-like ions. These values are used as the input for the

impurity transport code. In the second, theoretical part, we calculate the necessary diffusion

coefficients to reproduce the measured densities of the ionic abundances.

The density of the impurities is determined on the basis of the experimental and the theoretical

spectra of He-like iron. The theoretical spectrum includesthe new data from ADAS database

on the atomic processes in the specified ions. By fitting the theoretical and the experimental

spectra we obtain the concentrations of the ions. Finally, the one-dimensional transport code

is applied to obtain the radial profiles of the impurities andat the same time to determine the

diffusion coefficients.

Self-consistency of the approach is achieved by inclusion of the new radial profiles in the

modeling of the He-like spectra and iteration between experimental and theoretical part.

References

[1] P. Platz, Y. Margerit, J.-F. Artaud, M. Mattioli, B. Moulin Rev. Sci. Instr.70, 1 (1999)

∗partner in the Trilateral Euregio Cluster


Edge and core confinement in improved H-modes in ASDEX Upgrade

C.F. Maggi, Y.-S. Na1, R. Bilato, M. Brambilla, L.D. Horton, E. Poli, A.C.C. Sips,

A. Stäbler, G. Tardini and the ASDEX Upgrade Team

MPI für Plasmaphysik, EURATOM Association, D-85748 Garching, Germany1Korea Basic Science Institute, 52 Yeoeun-Dong, Yusung-Gu, Dejeon, 305-333, Korea

The improved H-mode developed at ASDEX Upgrade (AUG) is an interesting

scenario for ITER, since it combines high confinement (H98(y,2) >1 ) with high stability (N

> 2.5) in stationary discharges (longer than 40 x E or more than twice the current

diffusion time). Typically, improved H-modes are operated at low * and with Ti > Te.

Whereas ion temperature profiles are stiff in improved H-modes with the same

gradient length as in standard H-modes, one aspect of the confinement improvement with

respect to the reference ELMy H-mode scenario is density peaking. Performance

improvement due to density peaking is limited by impurity accumulation and the

concomitant increase in core radiation. Control of density peaking (and impurity

accumulation) has been established as a routine tool in AUG using central wave heating

(both ICRH and ECRH). Improved H-modes have also been obtained with strong central

ICRH (up to half of the total input power) with the goal of exploring conditions similar to

those of a reactor.

Modelling of these discharges is now available and can separate the effects of

electron and ion heating on density peaking in improved H-modes. Analysis of the ICRH

power deposition profiles is carried out with the TORIC code for first wave absorption and

a quasi-linear Fokker Planck solver for fast ions coupling to the bulk plasma. Initial

calculations of the ECRH deposition profile have been carried out using the TORBEAM

code. The neutral beam power deposition profiles are deduced by a NB Monte Carlo code

(FAFNER). The overall transport analysis is carried out with ASTRA using ITG core

turbulence transport models. Comparisons of the experimental profiles with ASTRA

simulations will be presented. In particular, the dependence of density peaking on

collisionality and the effect of Ti > Te will be investigated.

The other aspect of confinement improvement is the role of the edge transport

barrier (ETB). There is evidence that the contribution to the global confinement from the

ETB region increases with input power. Measurements will be presented showing the

variation of the pedestal parameters as the confinement is improved with increasing input

power and with varying fractions of NBI and ICRH. In this way it is hoped to develop a

complete picture of edge + core confinement in improved H-modes and its variation with

input power and heating schemes.


Observations on core turbulence and radial electric field

transitions in ASDEX Upgrade using Doppler reflectometry

G.D.Conway, C.Angioni, F.Ryter, J.Schirmer, A.Peeters, CFN Reflectometry and

ASDEX Upgrade Teams

Max-Planck Institut fur Plasmaphysik, Euratom-Association IPP, Garching,

D-85748, Germany

Core turbulence and radial electric field behaviour in the ASDEX Upgrade tokamak

are studied using microwave Doppler reflectometry. Whereas normal reflectometry is

sensitive to a broad turbulence wavenumber spectra centred on k⊥ ∼ 0, the poloidally

tilted antenna in Doppler reflectometry selects a specific non-zero k⊥ (via Bragg).

This results in a Doppler frequency shift fD in the measured S(k⊥, ω) spectra which is

directly proportional to the perpendicular (to B) rotation velocity u⊥ = vE×B + vphase

of the turbulence moving in the plasma. For edge electron drift-wave type turbulence

vE×B ≫ vphase for the typical probed k⊥ > 8 cm−1, which allows a straightforward

conversion of u⊥ to radial electric field Er. In the SOL u⊥ always flows in the ion

drift direction (i.e. +Er) but reverses across the separatrix (−Er) due to the pedestal

pressure gradient. In the core the direction and magnitude of u⊥ depends on the

plasma scenario and, particularly on the presence of momentum driven rotation by

neutral beam injection. In the absence of dominant beam driven rotation (e.g. ohmic

conditions) the core u⊥ reveals a strong monotonic variation with collisionality ν∗.

At low collisionality u⊥ is in the ion drift direction, but reverses smoothly to the

electron drift direction above a critical ν∗. This behaviour is not inconsistent with neo-

classical predictions for Er, implying that even for core ITG/TEM turbulence u⊥ is still

dominated by the E×B velocity. Turbulence effects are, nevertheless, evident. At high

collisionality the turbulence frequency spectra is excessively broadened (beyond that

due to rotational broadening alone) indicating a change in the underlying turbulence

k-spectrum. In electron heated plasmas a transition from TEM to ITG dominance is

predicted by gyro-kinetic calculations to occur at high density/collisionality, with a

corresponding change in the plasma response (density peaking etc.) to central electron

cyclotron heating. Initial attempts to directly measure the transition from TEM to

ITG via reversal of the turbulence phase velocity vphase show unexpected direction

shifts in fD when applying core ECRH. Alternate techniques to discriminate core

turbulence transitions are also discussed.


Ion ITB dynamics in ASDEX Upgrade

G. Tardini1, J. Hobirk1, C. Ludescher2, C. F. Maggi1, P. Martin1, D. McCune2,

A. G. Peeters1, A. C. C. Sips1, A. Stabler1, J. Stober1,

and the ASDEX Upgrade Team1

1MPI fur Plasmaphysik, Euratom Association, Boltzmannstr. 2, 85748 Garching, Germany

2Princeton Plasma Physik Laboratory, Princeton University, Princeton, NJ08543, USA

Internal Transport Barriers (ITBs) are the main scenario for steady state tokamak oper-

ation, due to the high fraction of bootstrap current and to the good energy confinement.

ITB feasibility and sustainment are crucial issues for the next step device ITER.

Ion temperature (Ti) ITBs in the tokamak ASDEX Upgrade are routinely obtained with

high Neutral Beam Injection (NBI) power at low enough electron density (ne). High

confinement is achieved with central Ti up to 25 keV, H98(y,2) ≈ 1.9 and βN up to 2.9.

However, a major drawback is set by the ITB’s limited lifetime of only several confine-

ment times (τE ’s). It will be shown in this paper that ASDEX Upgrade ITBs usually

collapse before the first Edge Localised Mode burst occurs, suggesting that the confine-

ment loss is due to a transport mechanism.

Ion heat transport is commonly believed to be dominated by the Ion Temperature Gra-

dient (ITG) driven instability, its suppression leading to ITB formation. Typical ITG

stabilisation mechanisms cannot be invoked for the plasmas considered here: the mag-

netic shear is close to zero but not negative, the plasma velocity shearing rate ωExB and

the Shafranov shift are not strong enough for the ITB to form.

In this paper we discuss a new mechanism for ITB formation: the dilution of thermal ions

due to the fast ion population. The suppression of the ITG mode has been accurately

calculated using a gyro-kinetic stability code (GS2) for the growth rate. Monte Carlo

simulations with the TRANSP transport code reconstruct the time dependent fast ion

population. Local values of nfi/ne above the GS2 threshold are found for ρtor ≤ 0.3,

consistent with the experimental ITB width. The proposed mechanism explains also the

ne threshold observed for the onset of ASDEX Upgrade ion ITBs.

NBI particle fuelling and thermalisation enhance ne on a beam slowing down time (τsd)

scale. This reduces nfi/ne also by limiting the beam penetration and shortening τsd.

Furthermore, Ti/Te, ωExB and the Shafranov shift decrease too as confinement degrades.

This runaway mechanism can explain the ITB collapse and predicts the ITB lifetime to

be of the order of τsd, comparable to a few τE ’s, as observed in the experiments.

The mechanism proposed in this paper has a strong impact on the ITB scenario for ITER.

Indeed, the large device size and the lesser NBI penetration are expected to prevent ITBs

unless strongly negative magnetic shear is sustained in a broad region. This is possible

only with a strong control of the current profile shape, which is a demanding requirement

for the hardware capability of ITER and a limitation for non-inductive operation.


Machine independent representation ofexperimental H-mode pedestal and divertor data

W. Suttrop1, G. D. Conway1, D. P. Coster1, L. D. Horton1, A. Kallenbach1, J. Lister2,

C. Roach3, T. H. Osborne4, P. Strand5, and M. Walters3

1Max-Planck-Institut fur Plasmaphysik, EURATOM Association, D-85740 Garching, Germany;2Centre de Recherches en Physique des Plasmas, Association Euratom-Confederation Suisse, Ecole

Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland3Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire, UK;4General Atomics, San Diego, CA 92186, USA;5Department of Electromagnetics and EURATOM/VR Association, Chalmers University of Technol-

ogy, S-412 96 Goteborg, Sweden

Extrapolation of tokamak performance to next step devices is based on data bases of ex-

perimental results from present machines. For scalar data such as the confinement time and

one-dimensional core profiles (e.g. electron and ion temperatures, heating power deposi-

tion) inter-machine databases are well established. However, H-mode pedestal and divertor

behaviour are important aspects that can significantly influence tokamak performance and

thus are studied intensively in inter-machine comparison experiments and numerical code

analysis. Due to the multi-dimensionality of the relevant experimental data a simple scalar

database model (such as implemented in relational databases) is not sufficient.

Based on previous work on the International multi-tokamak confinement profile database

(http://tokamak-profiledb.ukaea.org.uk) we investigate the possibility to represent

all quantities relevant for H-mode pedestal and divertor studies in a machine-independent

format. This data format is useful for inter-machine comparison, as it allows to access phys-

ical quantities in a unified way. Numerical code analysis can be based on a simple interface

to experimental data, thus avoiding the need to pre-process individual tokamak data with

machine-specific input processors. The common data format also permits easy visualisation

of corresponding experimental and simulation data.

The data types currently stored include profiles of pedestal electron and ion tempera-

tures, electron density, effective charge, all with original experimental data (including error

bars) and a regularising fit. The plasma equilibrium is represented by the poloidal flux on

a rectangular grid and the one-dimensional flux functions p

and FF

. Spectroscopic data,

for example observing deuterium recycling flux or impurity line radiation in the divertor, is

represented by start and and end points and aperture of the observation sightline.

The data is organised in a hierarchical tree structure. The individual branches can be

filled optionally, depending on the needs of a particular physics investigation. MDSplus

(www.mdsplus.org) is used to physically store data; however, other hierachically organised

storage formats can be used. The data structure and examples of applications are described.

So far, pre-processors have been implemented for the HELENA fixed boundary equilibrium

code and the ASCOT Monte-Carlo particle code. A port of more codes, e.g. the FLUSH

equilibrium toolbox, is underway. The data structure can be described formally using the

Extended Markup Language (XML). Tools for verification and tree-building based on the

XML description are presented. Data visualisation requirements define constraints on the

hierarchical format, application examples and issues are discussed.


Pattern recognition techniques in plasma turbulence imaging H Thomsen1, T Klinger1, R Koenig1, A Alonso2, C Hidalgo2

1 Max-Planck-Institut für Plasma Physik, EURATOM Ass., 17491 Greifswald, Germany 2 Laboratorio Nacional de Fusión. Asociación EURATOM-CIEMAT, 28040 Madrid, Spain

The availability of very fast framing CCD cameras with up to 1 million frames per second

enables the study of edge plasma turbulence by means of the Gas Puff Imaging (GPI)

technique [Zweben et al., Nucl. Fusion 44 (2004), p. 134]. The gas puff is used to increase the

fluctuation contrast with respect to the steady state radiation background. The light detected

by the camera primarily comes from the area illuminated by the gas puff, which reduces the

smear-out of structures due to the line-integrated view.

The evaluation of such data is a demanding task due to the large amount of data and the

complex dynamics. Moreover, for an objective turbulence characterization a statistical

treatment of the data is mandatory. In future steady-state fusion devices (like the Wendelstein

7-X stellarator under construction in Greifswald, Germany) an automatic evaluation is the

only perspective to process the huge amount of spatio-temporal data collected by turbulence

diagnostics.

In this paper we present pattern recognition methods, which carry the perspective of an

automatic turbulence characterization. The evaluation data is provided by a fast framing

camera (Ultima Pro 40k) recording with a rate of up to 40.500 frames per second which was

installed for a dedicated measurement campaign at the TJ-II stellarator. The edge plasma

turbulence is monitored in the visible light with a tangential view, exposing the complex

dynamics perpendicular to the magnetic field lines. The pattern recognition methods allow the

extraction of relevant turbulence features, e.g. structure sizes and life times. In contrast to

most fourier-based methods, not only the averages but also the distributions of these

quantities can be estimated. Flow maps are realized by object tracking. We demonstrate the

advantages of these methods for experimental data from the TJ-II stellarator.


EDGE TURBULENCE STUDIES AT TEXTOR DURING DYNAMICERGODIC DIVERTOR OPERATION BY MEANS OF

REFLECTOMETRY

A. Kramer-Flecken1, S. Soldatov2, C. Busch1, K.H. Finken1, H.R. Koslowski1, Y. Liang1,V. Vershkov2, R. Wolf1, O. Zimmermann1, and the TEXTOR–Team

1Institut fur Plasmaphysik, Forschungszentrum Julich GmbH,EURATOM Association, D–52425 Julich, Germany∗

2Nuclear Fusion Institute, RRC ”Kurchatov Institute”, Kurchatov Square, 123128 Moscow, Russia

The dynamic ergodic divetor (DED) has been installed recently at TEXTOR. The DEDconsists of a set of 16 coils mounted on the high field side (HFS) of the vessel. The coils arehelically wrapped around the HFS in that way that they match the magnetic field perturbationon theq = 3 surface. It can be operated at different currents in DC and AC operation.The DED has been operated in 3/1– and 12/4– configurations. In the 3/1–configuration theperturbation field directly effects the plasma in the confinement region, whereas in the 12/4–configuration the perturbation is restricted to the plasma edge only. For both cases the turbu-lence behavior is studied by means of O-mode reflectometry1 using the antennae array in theequatorial plane and on top of the vacuum vessel. With the help of reflectometry frequencyscans, the radial region influenced by the perturbation field, is investigated during DED oper-ation. The properties of high m–number quasi coherent (QC) mode and of the low frequencyturbulence is studied as function of electron density and plasma current in both DED config-urations. For a certainqa–value a suppression of the QC mode is found. Already before theQC mode is suppressed the poloidal correlation length and the center frequency of the modedecreases. At the same time the low frequency turbulence changes its rotation direction and alarge velocity shear is observed. In the 3/1 configuration and at the radial position where thechange from electron to ion diamagnetic drift is observed a reduction of the density fluctuationlevel for low kΘ is observed compared to the limiter case. At this position an increased tem-perature gradient is found, too. The propagation of the turbulence is a direct measurement ofthe poloidal plasma velocity as found in a comparison with the data from the RUDI diagnosticbeam2, measuring the poloidal velocity at the plasma edge. Therefore the radial electric fieldcan be estimated from the calculated poloidal velocity of the QC mode or the low frequencyturbulence. With the change in the rotation direction a change to a positive radial electric fieldis expected. The observed reduction in the turbulence for lowkΘ, following the analysis inthe work by Devynck3, can be explained by the radial separation of the magnetic field linesinduced by the perturbation of the DED4. With a slow 2 Hz modulation of the perturbationfield as well as with the use of the antennae array on top of the vessel the polidal structure ofthe ergodic layer is studied for various plasma conditions.

[1] A. Kramer–Flecken et al., Nucl Fusion44, (2004), 1143–1157[2] C. Busch et al.,this conference[3] P. Devynck et al., Nucl. Fusion42, (2002), 697–707[4] Ph. Beyer et al., Phys Plasmas5, (1998), 4271

∗partner in the Trilateral Euregio Cluster


Turbulent transport in the plasma edge in the presence of static

stochastic magnetic fields

D. Reiser1, B. Scott2

1 Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM

Association, Trilateral Euregio Cluster,D-52425 Jülich,Germany2 Max-Planck-IPP, EURATOM Association, D-85748 Garching, Germany

The technical option to ergodize magnetic fields in fusion relevant tokamak exper-

iments by externally induced magnetic perturbation fields offers the opportunity to

influence drift instabilities and therefore the turbulent behaviour of plasmas. Em-

ploying an electromagnetic four field model (n, φ , u‖

andA‖) the non-linear evolu-

tion of turbulence is studied for the plasma edge of TEXTOR-DED in the presence

of a static stochastic magnetic field, represented by a smallnumber of perturbation

modes resonant in the computational domain. The equations are solved numerically

by the DALF3 code for a fixed background plasma. Perturbationfields of varying

strengths (Chirikov-parameter below and above 1) are studied for cases of low and

high collisionality typical for drift wave driven or ballooning driven regimes. The

physical parameters like density, temperature, density gradient length and geomet-

rical dimensions are chosen close to realistic parameters of TEXTOR-DED dis-

charges, namelyn= 2·1019m−3, T = 100eV,B0 = 2T, q0 = 3, s= 2 R0 = 1.75m,

a = 0.45m, andL⊥

= 3cm for the low collisional case. The high collisional case

is studied leaving all parameters unchanged but choosing a density and temperature

of n = 6.5·1019m−3 andT = 30.8eV to keep the plasmaβ unchanged. The pertur-

bation field is approximated by three modes, namely 11/4, 12/4 and 13/4 to reflect

the situation close to theq = 3-surface in 12/4-mode operation of TEXTOR-DED.

In all cases considered a significant increase ofE×B-transport is found. But the

different regimes of low and high collisionality exhibit a different signature in that

the ballooning dominated case is less affected. For the mostpart the observed ef-

fects can be attributed to static contributions of the perturbations at resonant mode

numbers. By means of time averaging an approximation for thestationary solution

of the model equations is found. The time dependent pieces ofthe numerical results

show an increase (drift wave driven regime) or decrease (ballooning driven regime)

of the experimentally observable density fluctuations.


Effects of edge ergodization induced by DED on turbulence

and particle transport in TEXTOR

S. Jachmich1, Y. Xu1, M. Lehnen2, R. Weynants1 and the TEXTOR-Team2

Partners in the Trilateral Euregio Cluster (TEC): 1 Laboratoire de Physique des Plasmas – Laboratorium voor Plasmafysica,

Association 'Euratom-Belgian state', Ecole Royale Militaire – Koninklijke Militaire School, B-1000 Brussels, Belgium

2 Institute für Plasmaphysik, Forschungszentrum Jülich, Jülich, Germany

In TEXTOR the dynamic ergodic divertor (DED), which consists of a set of 16 coils wrapped

around the vessel at the high field side creates a perturbation field resonant to the q = 3

surface. In the recent campaign the DED has been operated with poloidal/toroidal mode

number equals 3/1. During the ramp-up of the coil-currents an onset of a m/n=2/1 tearing

mode, which is accompanied by a drop in the core plasma density and a flattening of the edge

is observed. Four different settings of the DED-currents have been studied: (1) the static case,

(2) slow sweep of the edge structure over the diagnostics, (3) AC co-DED operation with a

phase in the two coil currents such that a co-rotation is imposed and (4) AC counter-DED.

The "co-rotation” means with respect to the poloidal direction the ion diamagnetic direction

and with respect to the toroidal one the direction of the plasma current. A probe with 16

electrical pins has been used to monitor changes in the edge profiles of floating potential,

electron density, electron temperature and their fluctuations during all phases of the

discharges.

For all four cases the measurements show a reduction of the neo-classical ambipolar

electric field with increasing of the DED current, which can be explained by the enhanced ion

transverse conductivity. The drop in the electric field is accompanied with a decrease of the

poloidal rotation and can be allocated with the mode onset, except for the counter DED-AC

case, where no mode-onset is observed. Interestingly the fluctuations are reduced in case of

the static operation of the DED. The amplitudes in the power spectrum are lower in the

overall frequency range, which is up to 500 kHz. However, in case of the dynamic 1 kHz

operation the drag of the edge structure causes the rotation to slow down and enhances the

edge turbulence, which is in agreement with theoretical predictions [2]. On the contrary,

when DED-AC is operated in the counter direction, the turbulent particle transport is reduced

and even reverses sign. In this contribution we will present our experimental findings on

electrostatic turbulence in various DED-operating modes.

[1] K. Finken, et al., 31st EPS-Conference on Plasma Physics, London, (2004). [2] P. Beyer, et al., Plasma Phys. Contr. Fusion 44 (2002), p. 2167.


Profile robustness and routes to turbulence in the helimak configuration

K. Rypdal1, O. E. Garcia2

1Department of Physics, University of Tromsø, Norway2Department of Optics and Plasma Physcis, Risø National Laboratory, Denmark

The helimak configuration is a toroidal plasma with a weak vertical magnetic field added

to a purely toroidal field. Using the magnetic field strength B as a control parameter in a

hot-cathode produced Helimak plasma, it is demonstrated that there is a threshold BT for

electrostatic flute modes (k|| =0) on the low B-field side of density maximum. This is

really a threshold in the gradient of the electron density profile, since this profile is

controlled by the magnetic field in the steady flow state appearing for B<BT. For B>BT

radial profiles of electron pressure are exponential on both sides, but on the low field side

the scale-length approaches a constant value as B is increased. The formation of this

resilient profile occurs as power spectra of electrostatic fluctuations evolve from purely

monochromatic at threshold, via a period doubling route to turbulence when B>> BT.

The helical magnetic field lines introduce a periodicity condition for the flute modes in

the vertical direction, introducing a fundamental wave-number kV= BT /RBV . This

corresponds to a mode coiled up like a snake. In the long wave-length approximation the

unstable flute modes take the form of purely growing convection cells where the spatial

density and potential oscillation are 90O out of phase, giving rise to radial plasma

transport. If the back-reaction of this anomalous transport on the density profile is taken

into account, a closed model of three autonomous first order ordinary differential

equations can be formulated, which is very similar to the celebrated Lorenz model.

Qualitatively this model describes the period doubling route to chaos observed

experimentally, but the long wave-length limit is inconsistent close to instability

threshold where the dynamics take place, and predicts an incorrect threshold. The remedy

of this situation requires a more complicated model requiring five equations. Work along

these lines are presented and compared to experimental results.


Gyrofluid turbulence computations in the edge and SOL regions of

tokamak plasmas using realistic magnetic field geometry

T.T. Ribeiro1, B. Scott2 and D. Coster2

1 Centro de Fusão Nuclear – EURATOM/IST Association,

Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal

2 Max-Planck-Institut für Plasmaphysik, EURATOM Association,

D-85748 Garching bei München, Germany

The boundary of tokamak plasmas is characterised by electromagnetic interactions between

wavelike and fluidlike motions on space scales down to the ion gyroradius. We use the gyrofluid

model GEM3 to investigate electromagnetic turbulence and the associated transport phenomena

both in the edge and scrape-off layer (SOL) of such region of the plasma. The effect of a realistic

tokamak geometry is isolated by comparing the results obtained for an edge plasma (closed

field lines) using a simplified geometry model retaining only the poloidal dependence of the

curvature operators, with the ones obtained for the same region using a faithful description of a

diverted equilibrium magnetic field configuration of the ASDEX Upgrade tokamak. The SOL

region is then studied, within the same realistic geometrical description. First, we use a standard

Debye sheath model to account for the presence of the material plates of a limiter, within the

region inside the separatrix. Then, the simulations are performed in the same manner using

the geometrical description corresponding to the region outside the separatrix, where the flux

surfaces are geometrically open. In the former, the influence of different poloidal positions of the

limiter is studied by changing the place, along the field lines, where the Debye sheath boundary

conditions are applied. In the latter, these are always applied at the positions corresponding to

the actual divertor plates. The issue of ensuring that no relevant space scales are excluded from

the simulations at positions radially near the X-point singularity, where the local magnetic shear

becomes infinite, is discussed throughout the work.


Study of edge flows and transport during emissive electrode biased

discharges on ISTTOK

H. Figueiredo, C. Silva, I. Nedzelsky, B. Gonçalves, J.A.C. Cabral, C.A.F. Varandas

Associação Euratom/IST, Centro de Fusão Nuclear, Instituto Superior Técnico

1049-001 Lisboa, Portugal

A velocity shear stabilization mechanism has been proposed to be responsible for an

improvement in plasma confinement. A clear correlation between the reduction of turbulence

and the modification of radial electric fields induced by bias has been observed in several

experiments [1]. This contribution presents and discusses biasing experiments on ISTTOK

tokamak mainly focussed on the correlation between the modifications in edge transport and

the ExB flows.

The influence of emissive electrode biasing on plasma confinement has been

previously investigated in detail on the ISTTOK [2]. Emissive electrodes produce a large

current density, allowing therefore an efficient control of the edge radial electric field for

both polarities. Emissive electrode biasing experiments revealed that although the edge radial

electric field induced by emissive electrode bias is of the same magnitude for both polarities

(up to ±15 kV/m), a strong improvement in particle confinement is only observed for

negative bias.

A set of movable electrostatic probes (rake, Gundestrup and a multi-pin probe for

turbulence measurements) provides detailed information of the poloidal and toroidal flows,

electron temperature, density, radial electric field and the fluctuations induced particle flux

with a high temporal resolution. The modifications in the plasma flows induced by biasing

have been investigated using the Gundestrup probe. Just inside the limiter position, the

modification in the perpendicular Mach number is in opposite directions for positive and

negative bias. The ExB radial profiles derived from the Gundestrup and rake probe will be

compared and correlated with the modification observed in the edge transport. Furthermore,

the statistical properties of the edge transport will be investigated in order to understand the

different behaviour observed for positive and negative bias.

[1] G. Van Oost, et al., Plasma Phys. Control. Fusion, 45 (2003) 621

[2] C. Silva, et al., Nucl. Fusion 44 (2004) 799


Transpor t and fluctuations dur ing electrode biasing on TJ-II

C. Silva1, M.A. Pedrosa

2, C. Hidalgo

2, E. Calderón

2, B. Gonçalves

1, J. Herranz

2,

K. McCarthy2, I. Pastor

2, O. Orozco

2

1Associação Euratom/IST, Centro de Fusão Nuclear, Instituto Superior Técnico 1049-001 Lisboa, Portugal

2Asociación Euratom/Ciemat, 28040 Madrid, Spain

The influence of limiter biasing on plasma confinement, turbulence and plasma

flows have been previously investigated in detail on the TJ-II stellarator [1]. Experimental

results showed that it is possible to modify global confinement and edge plasma parameters

with both positive and negative biasing and showed evidence of electric field induced

improved confinement via multiple mechanisms. Electrode biasing is expected to introduce

more substantial changes in energy and particle confinement than limiter biasing as it has

the advantage of forcing an electric field in the edge plasma.

Figure 1: Time evolution of the plasma density, biasing voltage, edge potential, ion saturation current, Isat level of fluctuations and H-alpha signal for a discharge with positive electrode bias.

This contribution describes the behaviour of the plasma during electrode biasing

experiments on TJ-II. As the bias is applied, the bias current amplitude increases rapidly for

both polarities and the floating potential at the plasma edge is also modified in a rather short

time scale (<50 os) leading to a strong modif

region just inside the limiter. The plasma

response is different at densities below and

above the threshold value to trigger the

spontaneous development of ExB sheared

flows [2]. At low densities, the edge plasma

potential is fully controlled by external

biasing. In this case, strong increase in

plasma density and reduction in edge

fluctuation level and H

ication in the edge radial electric field in the

.,

[2] C. Hidalgo, M. A. Pedrosa et al., Phys. Rev. E 70, 067402 (2004); M.A. Pedrosa et

al., accepted for publication in Plasma Phys. Controlled Fusion

c signals is observed

during biasing (Fig. 1). At higher densities

edge plasma potential profiles are

determined not only by external biasing but

also by the electric fields spontaneous

developed. Although an improvement in

particle confinement is observed for both

polarities, a larger increase is observed for

negative electrode bias. In this contribution,

the edge turbulent transport and in

particular the statistical properties of the

edge fluctuations are described during

electrode bias for both polarities. [1] C. Hidalgo, M. A. Pedrosa et al

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Plasma Phys. Control. Fusion 46 (2004) 287


Effects of impur ities on dr ift wave based par ticle transpor t

P. Strand1, H. Nordman

1, A. Eriksson

1, W. A. Houlberg

2, J. Weiland

1

1 Dept of Radio and Space Science, EURATOM/VR Association, Göteborg, Sweden 2 Oak Ridge National Laboratory, Oak Ridge, USA

Drift wave based descriptions of energy confinement in tokamaks have developed over the

last decades towards a standard model for anomalous ion energy transport in the gradient

region of the plasma. This holds true mainly for the main ion species although combined

descriptions of ITG, TEM and in some cases ETG modes provide reasonable estimates also

for the electron transport channel [1, 2, 3]. These models have traditionally been used much

less for studies of particle transport. A new implementation of the Weiland model is

extending the original formulation to contain an arbitrary number of ion species [4].

Aspects of anomalous particle transport in burning plasmas that can be assessed with the

model include separate deuterium and tritium transport, helium ash transport and removal

as well as low-Z impurity accumulation. Initial work with the extended version of the

implementation (EDWM) [5] show that the deuterium and tritium can have different

characteristics in going from tritium trace levels to a 50-50 mix of DT. In the fusion reactor

relevant regime the local gradients become important and even for similar D and T density

gradients the slight asymmetry in the first order FLR term tend to drive diffusivities apart.

In this case however the change in transport is such that the net effect would be towards

equilibration of length scales. The relative importance of neoclassical and anomalous

particle transport depends on the charge number of the species being studied. The different

scaling with charge number in drift wave based and neoclassical models tend to favour a

stronger component of neoclassical transport for higher Z impurities. The detailed balance

between the two descriptions will be discussed and comparisons made with the NCLASS

[6] model. The composition of the plasma has an impact also on the stability of the main

ion drift wave descriptions and detailed results on the linear stability of DT plasma in

presence of impurities will be discussed.

[1] J. Weiland, IoP Publ., Bristol, 2000, "Collectives Modes in Inhomogeneous Plasma”.

[2] R. E. Waltz, G. M. Staebler, W. Dorland, et al., Phys. Plasmas 4, 2482 (1997).

[3] G. Bateman, A.H. Kritz, J. Kinsey, A. Redd, J. Weiland, Phys. Plasmas 5, 1793 (1998).

[4] P.I. Strand, et al., 31st EPS Conference, ECA Vol.28G, P-5.187 (2004).

[5] H. Nordman, et al. Accepted for publication in Plasma Phys. Control. Fusion.

[6] W.A. Houlberg, et al, Phys. Plasmas 4 (1997) 3230


! ∀ # ∀ ∀ ∃ ∀ ∀ ∀ ∃ ∀ ∃ %&∋ ∃ ∀ ( ∃ ! ∀ ! ∀


Large-scale flows and coherent structure phenomena

in flute mode turbulence

Ingmar Sandberg1, Zhanna N.Andrushchenko2 and Vladimir P.Pavlenko2

1 National Technical University of Athens, Association Euratom-Hellenic Republic, Greece 2 Uppsala University, Euratom-VR Fusion Association, Uppsala, Sweden

It is already well accepted, that nonlinear interaction of short-scale fluctuations in magnetized plasma can generate low-frequency, large-scale nonlinear structures (so called zonal flows and streamers) that play an important role in controlling plasma transport properties in magnetic confinement systems. Zonal (or poloidal) flows correspond to structures which spatially depend on the radial coordinate (the coordinate along the axis of plasma inhomogeneity), while radial flows or streamers are radially elongated structures which spatially depend on the poloidal coordinate. On the other hand, these large-scale structures can modulate and regulate the turbulence dynamics itself via the nonlinear coupling to the small-scale fluctuations, so that each cannot be addressed in isolation. So, the plasma turbulence consisting of these two disparate components is expected to be in self-regulated state mediated by shear flows. Therefore, the dynamics of such coupled system becomes central in understanding of turbulent transport in fusion devices.

Here we investigate the generation of large-scale flows in flute mode turbulence via Reynolds stress. The interaction between disparate scales of the turbulence is described by employing the evolution equations for the mean flow and the wave kinetic equation for an action-like invariant of the wave turbulence with slow varying parameters due to the mean sheared flows. The solution of these equations results in the determination of a stability criterion in terms of the density spectra of flute oscillations. Two limited cases corresponding to resonant and coherent (hydrodynamic) type of instabilities are considered and it was shown that coherent instability has a larger growth rate compared to that of resonant instability. Furthermore, the formation of coherent structure that corresponds to a propagating shear layer “domain walls” between regions of different flow velocities is depicted. This solution is known as “switching” wave or “kink” soliton. The characteristic parameters of this solution are determined by the value of the group velocity and by the spectral density of background fluctuations.


I.G.J. Classen1, M.W. Jakubowski2, A.J.H. Donné1, K.H. Finken2, M.J. van de Pol1, C.W.

Domier3, N.C. Luhmann Jr.3, H.K. Park4, E. Mazzucato4, T. Munsat5, and TEXTOR team2

1. FOM-Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, PO Box 1207, 3430 BE Nieuwegein, The Netherlands, www.rijnh.nl*

2. Forschungszentrum Jülich GmbH, Institut für Plasmaphysik, Association EURATOM-FZJ, D-52425 Jülich, Germany*

3. University of California at Davis, Dept. of Applied Science, Davis, California, U.S.A. 4. Princeton Plasma Physics Laboratory, Princeton, New Jersey, U.S.A.

5. University of Colorado at Boulder, Colorado, USA *Partners in the Trilateral Euregio Cluster

Direct 2D measurements of electron temperature with a high spatial and temporal

resolution are possible with the ECE imaging (ECEI) diagnostic [1] on the TEXTOR

tokamak. ECEI uses wide aperture optics to image a vertical slice of the plasma onto an

array of 16 receivers. Each receiver is treated as a conventional ECE radiometer with 8

frequency channels, giving an 8 (radially) by 16 (vertically) array of sampling volumes in

the poloidal plane, representing about 8 by 16 cm in the plasma. The system is wideband

tuneable from 85 to 130 GHz to match a wide variety of magnetic field conditions. With the

ECEI system one can directly explore the two-dimensional nature of plasma structures in a

single measurement with a time resolution of up to 500 kHz.

ECEI has been used to measure the effects of the Dynamic Ergodic Divertor (DED) [2]

on the edge electron temperature. The DED experiment on TEXTOR explores the influence

of perturbation fields on the plasma. The DED consists of 16 helical coils on the high field

side, which generate perturbation fields resonant with the q=3 surface. Among the

observations with ECEI close to the LFS plasma edge during DED 12/4 operation are a

general temperature drop when the DED is switched on and the appearance of poloidal

structures in temperature in the so called laminar zone (the region of the plasma where the

perturbed magnetic field lines have short connection lengths to the wall). A comparison of

the observed structures with model calculations [3] will be given. Also the influence of the

DED on the measured temperature fluctuations (MHD and turbulence) will be addressed.

[1] H. Park et al., Rev. of Sci. Instrum. 74, 4239-4262 (2004). [2] Special Issue, Fusion Eng. Design 37 (1997) 335. [3] M.W. Jakubowski et al., Nucl. Fusion 44 (2004) S1-S11


Influence of an ergodic field in the plasma edge on the global plasma

rotation at the TEXTOR tokamak

M. De Bock1, C. Busch

2, I. Classen

1, K.H. Finken

2, R. Jaspers

1, S.K. Varshney

1,

M. von Hellermann1 and the TEXTOR team

1 FOM-Institute for Plasma Physics Rijnhuizen

*, Assosiation EURATOM-FOM, The

Netherlands, www.rijnh.nl

2 Institut für Plasma Physik

*, Forschungszentrum Jülich GmbH,

Association EURATOM-FZJ, 52425 Jülich, Germany

* Partners in the Trilateral Euregio Cluster

At the TEXTOR tokamak (R=1.75, a=0.47) a Dynamic Ergodic Divertor (DED) is

installed, allowing ergodization of the plasma edge with a static or dynamic perturbation

field1. The main objectives of this DED are controlling the heat and particle flow out of

the plasma and influencing plasma rotation. The latter will be discussed here. Charge

exchange recombination spectroscopy has been used for measurements of the toroidal

plasma rotation in the plasma core (r/a up to 0.6). First measurements done early 2004

proved that the perturbation field of the DED influences the global plasma rotation2,3

.

The experiments presented here investigate in more detail the effect of the DED field on

global plasma rotation. The effect of different modes of DED operation – ergodic field

with mode components m/n = 3/1 and 12/4, static and rotating perturbation field – are

presented, along with the influence of plasma parameters – beta poloidal, plasma current,

momentum input – on the rotation induced by the DED field. Simultaneous

measurements of toroidal and poloidal plasma rotation, electron temperature and density

and MHD frequencies have been performed, in order to investigate the relation between

plasma rotation, MHD rotation and pressure gradients.

The effects of the perturbation field on the plasma rotation can be categorized in two

different regimes: an increase of toroidal rotation in the direction of the plasma current as

long as the DED field amplitudes at the q=2 surface stay below the threshold for exciting

a 2/1 tearing mode; and a flattening of the rotation profile between the q=2 and q=1

surfaces once this 2/1 tearing mode is excited. A model based on changes in the edge

electric field, has been proposed to explain the increased plasma flow before 2/1 mode

onset. An explanation for the change in plasma rotation due to the 2/1 tearing mode could

be found in the coupling of the tearing mode to the perturbation field.

[1] Special Issue, edited by K. H. Finken, Fusion Eng. Des. 37, 335 (1997).

[2] M. De Bock et al, 31st EPS Conference on Plasma Phys., ECA Vol. 28G, P-1.117 (2004)

[3] K.H. Finken et al, Phys. Rev. Lett. 94, 015003 (2005)


Temperature gradient effects on magnetic stochastization

Hugo J. de Blankand Emiel V. van der Plas

FOM-Institute for Plasma Physics Rijnhuizen,

Association Euratom-FOM, Trilateral Euregio Cluster,

P.O. Box 1207, 3430 BE Nieuwegein, The Netherlands, www.rijnh.nl

Magnetic reconnection is a key mechanism in transport processes in weakly collisional plas-

mas, both in space and in magnetic fusion experiments. When collisional dissipation is weak,

resistive reconnection cannot always explain the observedreconnection rates. However, faster

than resistive reconnection rates are possible due to electron inertia. Parallel electron com-

pressibility can further accelerate this process, yielding fast reconnection rates comparable with

those observed in tokamak plasma instabilities [1].

In order to study the effects of magnetic reconnection on energy confinement, it is important

to describe the effects of temperature gradients on reconnection. The presence of a temperature

gradient makes it necessary to describe the reconnection process of field lines that have different

temperatures. In a collisionless plasma, this requires a kinetic description of the electrons.

Using such a model it is found that a temperature gradient perturbs the vorticity and current

distributions in the reconnection layer [2] and thus the entire magnetic island geometry [3].

Specifically, it is found that due to the temperature gradient, the magnetic perturbations of

growing as well as saturated island chains have a poloidal phase-shift that varies with the radial

coordinate. This has consequences for the stochastizationof tokamak magnetic fields. During

the growth of neighbouring island chains, the temperature gradient will modify the positions

of secondary and higher-order island chains, thereby altering the onset of stochasticity and de-

struction of the last KAM-torus.

[1] M. Ottaviani and F. Porcelli, Phys. Rev. Lett.71, 3802 (1993).

[2] H.J. de Blank and G. Valori, Plasma Phys. Control. Fusion45, A309 (2003).

[3] E.V. van der Plas and H.J. de Blank, 31st EPS Conference on Plasma Phys. London,

28 June – 2 July 2004 ECA Vol.28G, P-2.073 (2004)


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Non-ideal MHD effects on the nonlinear growth of m = 1 internal modes

M.-C. Firpo

Laboratoire de Physique et Technologie des Plasmas (C.N.R.S. UMR 7648),

Ecole Polytechnique, 91128 Palaiseau cedex, France

For reduced MHD models in cylindrical geometry, we consider the onset of the nonlinear

evolution ofm = 1 internal modes and propose a quantitative dynamical description for their

nonlinear growth rate before saturation. In this matter, the purely resistivem = 1 mode [1]

(with ∆′ = ∞) serves as the minimal relevant case for studying non-ideal effects [2, 3]. Then

we consider the two-fluid reduced magnetohydrodynamic description, that is relevant for high-

temperature fusion plasmas, provided by Hazeltine’set al. four-field model [4]. We propose an

explanation, together with a quantitative and predictive modeling, of the enhanced, and even

explosive, nonlinear growth rates observed in this case [5]. This involves the derivation of the

linear eigenfunctions [6] for the initial conditions used in Ref. [5]. The analysis tracks self-

consistently the instantaneous location of the critical layer where non-ideal effects play a major

role and control plasma dynamics.

References

[1] B. Coppi, R. Galvão, M.N. Rosenbluth and P.H. Rutherford, Sov. J. Plasma Phys.2, 3276

(1976)

[2] M.-C. Firpo and B. Coppi, Phys. Rev. Lett.90, 095003 (2003)

[3] M.-C. Firpo, Phys. Plasmas11, 970 (2004)

[4] R.D. Hazeltine, M. Kotschenreuther, and P.J. Morrison, Phys. Fluids28, 2466 (1985)

[5] A.Y. Aydemir, Phys. Fluids B4, 3469 (1992)

[6] E. Mury and Y. Pertot, Report, Magistère de Physique d’Orsay (2004)


Neoclassical tearing modes in the presence of sheared flows

A. Sen1, D. Chandra1, P.Kaw1 , M.P.Bora2 , S. Kruger3 1 Institute for Plasma Research, Gandhinagar, India

2 Physics Dept., Gauhati University, Guwahati, India 3 Tech-X, Boulder, CO, U.S.A.

The influence of equilibrium shear flows on the evolution of neoclassical tearing modes is

an important issue for future long pulse experiments on tokamaks and for reactor grade

machines like ITER. Sheared flows can be generated in a tokamak plasma due to a variety

of reasons, such as due to neutral beam injection, ion cyclotron heating and self-consistent

drift turbulence. A number of past studies have examined the effect of flows on classical

tearing modes, particularly in the linear regime and for simplified geometries. There have

also been a few nonlinear studies of the classical tearing mode but the problem is quite

complex, particularly in realistic toroidal geometries, and is an important area of present

and future study for major numerical initiatives such as NIMROD. A detailed

understanding of the evolution of NTMs in the presence of flows is still lacking. In this

work we study certain aspects of this problem through numerical solutions of a set of

generalized reduced MHD equations that includes viscous force effects based on

neoclassical closures. Our principal findings are that in general differential flow has a

strong stabilizing influence leading to lower saturated island widths for the classical tearing

mode and reduced growth rates for the neoclassical modes. Velocity shear on the other

hand is seen to make a destabilizing contribution. We delineate the contributions of various

linear and nonlinear terms in the model equations towards this evolution process and also

compare our results with some of the present experimental findings

[1] ITER Physics Expert Group on Disruptions, Plasma Control and MHD, ITER Physics

Basis Editors, Nucl. Fusion 39 2251 (1999).

[2] S.E. Kruger, C.C. Hegna and J.D. Callen, Phys. Plasmas 5 (1998) 4169.

[3] X.L. Chen and P.J. Morrison, Phys. Fluids B 4 (1992) 845.


Statistical Analysis of the equilibrium configurations of W7-Xstellarator using Function Parametrization

A.Sengupta1, J.Geiger2, P.J.McCarthy1

1Dept. of Physics, University College Cork, Association EURATOM-DCU, Cork, Ireland2Max-Planck-Institut f. Plasmaphysik, Euratom Association, Greifswald, Germany

W7-X stellarator, under construction at IPP-Greifswald, is being designed to demonstrate

the steady state capability of fusion devices. Due to the pulse length involved, real time moni-

toring and control of the discharges is a crucial issue in steady state operations. For W7-X, we

have planned a sequence of in-depth analyses of the magnetic configurations which, ultimately,

will lead to a proper understanding of plasma equilibrium, stability and transport. It should

also provide insight into the parametrization of the various plasma-related quantities which is

important from the point of view of real time study.

The first step in our sequence of analyses involved a study of the vacuum configuration,

including the detectable magnetic islands, of W7-X [1]. We now proceed to the scenario at finite

beta considering full magnetohydrodynamic (MHD) equilibria based on vmec2000 calculations.

A database consisting of nearly 10000 equilibria was calculated on the same parameter space for

the coil current ratios as in [1]. The parameters which were varied randomly and independently

consist of the external coil current ratios (6), the parameters of the profiles (as functions of

normalised toroidal flux) of plasma pressure and toroidal current (4+4), and the plasma size

(aeff ) which was required to vary the plasma volume. A statistical analysis, using Function

Parametrization (FP), is to be performed on a sample of well-converged equilibria. The plasma

parameters were varied to allow a good FP for the expected values in W7-X, i.e. volume-

averaged < β > up to 5% and toroidal net-current of up to ± 50 kA for a mean field strength

of about 2 T throughout the database. The profiles were chosen as a sequence of polynomials

with the property that the addition of a higher order polynomial would not change the lower

order volume-averaged moments of the resulting profile. The aim of this was to try to avoid

cross correlations in the independent input parameters for the database generation. However,

some restrictions had to be incorporated in order to maximize the number of converged vmec-

runs with randomly generated inputs. Therefore, the peaking factor βax/ < β > for the

pressure profile was restricted to avoid values of βax > 12%. This is reasonable in view of

experimental scenarios where large peaking factors are usually connected with low values of

< β >. Additionally, the central current density was limited in order to avoid very small values

of central iota. This was to ensure a reasonable vmec-convergence. We would present in detail

the basis of our dataset and a statistical description of the resulting dependent properties, such

as the profiles of the rotational transform and the differential volume V ′ as well as those of the

leading order Fourier coefficients for the geometry and the magnetic field strength.

[1] A.Sengupta, et al., (2004) Nucl. Fusion 44 1176


First Results from a New RFP Device with Very Small Aspect Ratio

K. Hayase

National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan

A new RFP device with a very small aspect ratio of A=2.1, TPE-QS, was constructed and

the initial experiment has started. We present the objectives and the first experimental results

of this novel compact RFP device. The aspect ratio, A=2.1, is much smaller than those of

existing and/or ever existed devices (A>3). Since qA~constant in RFP, rational surfaces

appear more diversely at a smaller A, e.g., q=1/4 at Ψ=0.4, q=1/5 at Ψ=0.6, ..., at A=2.1. This

means a dynamo process is sustained with a fewer number of mode (the reduction of

stochastic region), hence the improvement of confinement is expected. Also the loop voltage

could be reduced as A is decreased. The experiment is planned to examine these arguments

and explore a new operating regime in RFP [1]. In the design and construction, modification

of old TPE-2M device is considered. The designed device parameters of minimized aspect

ratio are; R/rw=0.53m/0.25m, A=2.1, Ip=100kA, Φ=0.25Wb. A compact and high voltage

center coil (0.05m thick, V=18kV, inner poloidal coil and outer toroidal coil) and an

aluminum vacuum vessel (t=0.025m) are newly developed. The construction of the device

has been completed successfully [2], and the RFP plasma experiment was started at Ip~50kA

after many shots of cleaning discharge. In the initial series of experiment, a substantial

extension of stable operating range in the F-Θ diagram is newly found. A stable discharge is

obtained even at Θ=2.5. The highest limit of Θ is 3.5. The minimum Vloop is ~30 V after the

boronization of wall surface in this experimental series. It is still decreasing with shots. The

mode structure and its behavior are measured in a wide range of F and Θ values. The main

poloidal mode number is m=1, and the main toroidal mode number is normally two (n=4, 5)

or three (n=4 to 6) as expected by simulations. The discharge with single or quasi-single

toroidal mode number n=4 is observed only in the low F (~-0.1) to F=0 region. In

comparison with the multi-mode case, the Bp fluctuation amplitude is larger but it shows a

coherent (sinusoidal) oscillation. Aside these discharges, a quiescent discharge with lower

fluctuation amplitude, but with multi-mode is observed in some cases. The profile of toroidal

flux generation (m=0 mode) indicates a good toroidal uniformity (n=0) in almost all cases.

Now the experiment is going to higher Ip range, and the new data will also be added.

[1] K. Hayase et al., FEC2002, ICP-09 (Lyon, 2002).

[2] K. Hayase et al., J. Plasma Fusion Res., 80 (2004) 721.


MHD instabilities observed in extreme reversed shear discharges on

JT-60U

M. Takechi,T. Fujita, Y. Ishii, T. Ozeki, G. Matsunaba, T. Suzuki, A. Isayama, JT-60 Team

Japan Atomic Energy Research Institute, Naka-city 319-0193, Japan

A reversed shear (RS) plasma is expected as a discharge of advanced scenario of ITER be-

cause it has good confinement and large bootstrap current fraction. It is understood that dis-

ruption atqmin ∼ 2 βN ∼ 2 is caused by stability limit of n=1 ideal kink ballooning mode.

However RS plasma with strong ITB disrupts frequently even at lowerβN . By now, low beta

disruption is explained by double tearing mode, which is obtained numerically, or resistive in-

terchange mode, and these are MHD instabilities atqmin and around ITB. However these cannot

explain all of observed low beta disruption. Consequently, to understand the cause of the low

beta disruption, we scrutinize the MHD instabilities of RS plasmas with strong ITB and central

flat pressure by measuring precious plasma current profile and MHD fluctuations. We mainly

observed two type of disruptions. One is the disruption without precursor atqsurf ∼ integer.

The other is the disruption withn = 1 precursor ofγ > 10 ms. To explain these characteristics

of disruption, we introduce the simple model such as, disruption occurs when the both MHD

instabilities at plasma surface and at safety factor being equal to surface mode are unstable [1].

0

1

2

3

4

4.5 5 5.5

N

unstable

stable stable

βN

qsurf

Figure 1: The preliminary result of ideal

MHD stability with ERATO code. The

circles and the crosses denote stable and

unstable, respectively

This simple model can explain almost all ob-

served disruption by two process. One is the sur-

face mode triggered disruption, which occurs when

qsurf change, corresponding q surface at ITB layer

change discretely. The other is the internal mode

triggered disruption, which occurs when corre-

sponding q surface become unstable gradually. The

preliminary result of ideal MHD stability with ER-

ATO code is shown in (Fig. 1). If the plasmas satisfy

the condition of the simple model, even the plasmas

with very lowβN are unstable at just below integer.

References

[1] M. Takechi et.al., Proceedings of the 20th

International Conference, Vilamoura, 2004,

IAEA-CN-116/EX/P2-32,(2004).


Modeling of MHD Stability Consistent to the Transport

T.Ozeki1, N. Aiba1, N.Hayashi1, T. Takizuka1, M.Sugihara2, N.Oyama1

1 Japan Atomic Energy Research Institute, Naka-shi, Ibaraki-ken, Japan 311-0193

2 ITER International Team, Naka JWS, Naka-shi, Ibaraki-ken, Japan 311-0193

Modeling of the MHD stability consistent to the transport is essential issues for

burning plasma simulations. Especially, Edge Localized Mode (ELM) is important from

viewpoints of the heat load on the divertor plate, the plasma confinement and the plasma

control for steady state. The ELM phenomena are considered to be induced by the high-n

ballooning mode due to the large pressure gradient or by the medium-n peeling mode due to

the large edge current. To evaluate the effect of the time dependent ELM phenomena on the

confinement of burning plasma, here we develop the integrated transport simulation model

using both of the 1.5D transport code TOPICS and the linear MHD instability code ERATO-

J/MARG2D [1].

TOPICS code solves the 1D transport equation, the current diffusion equation and the

2D MHD Grad-Shafranov equation for the real configuration, using the heating and current

drive source such as NBI and RF. Diffusivities in the transport equations consists of ion

neoclassical diffusivity by the matrix inversion method and some kind of anomalous

diffusivity, such as the ballooning mode type micro-instability, GLF-23 model and MMI

model etc.

MHD instabilities are analyzed by the linear ideal MHD stability code ERATO-J or

MARG2D, iteratively with the transport code TOPICS. MARG2D code solves the eigen-

value problem associated with the 2D Newcomb equation. MARG2D is applicable for

medium-n modes stability analysis and its calculation is the very fast. Results of the low n

mode of MARG2D agree with those of ERATO-J.

Self-consistent simulation is realized by the iterative calculation of MHD stability and

the transport. MHD stabilities of low-n and high-n modes are checked on the each time steps

of the transport simulation. When the modes become unstable, the plasma pressure and the

current density are expelled in the region of the eigen-function of the unstable mode. The

duration of the instability and the re-building of the pressure and current density are adjusted

based on the interval and the amount of ELMs observed in JT-60U. Here, we discuss the

validity of the model for various type ELMs, and also the collapse event.

[1] S. Tokuda, Phys. Plasmas 6 (8) 1999.


Simulation Modeling of Fully Non-Inductive Buildup Scenario

in High Bootstrap Current Tokamaks without Center Solenoids

Y. Nakamura1)

, H. Tsutsui2)

, K. Tobita1)

, N. Takei2)

, Y. Takase3)

, T. Ozeki1)

and S.C. Jardin4)

1)Japan Atomic Energy Research Institute, Ibaraki, 311-0193, Japan

2)Research Lab. for Nuclear Reactors, Tokyo Institute of Technology, Tokyo 152-8550, Japan

3)Department of Complexity Science and Engineering, The University of Tokyo,

Chiba, 277-8561, Japan

4)Princeton Plasma Physics Laboratory, Princeton, P.O. Box 451, New Jersey 08543, USA

Non-inductive techniques to establish, maintain, control and modify the current distribution

have been expected for promising such the economical reactor concepts as low aspect ratio

tokamak without center solenoids (CS) [1]. However, the CS-less tokamak has a drawback of

the longer natural timescale for the non-inductive current buildup with MHD stability than the

totally inductive buildup, while the significant advantage is its compactness [2]. Therefore, the

simulation modeling of the long-duration evolution of high bootstrap (BS) current plasmas

directly coupled with shaping coils is required to establish a fully non-inductive, hybrid current

drive scenario with the help of external RF current drive.

Taking the transport improvement being consistent with the magnetic shear profile and the

consequent ITB (Internal Transport Barrier) formation into consideration, time-evolution of the

current buildup was investigated via axisymmetric MHD simulations using Tokamak

Simulation Code (TSC) [3] with GLF23 and CDBM transport models [4, 5]. It was shown that

a plenty of non-inductive currents can afford both to buildup plasma current and to recharge

shaping coil currents against boosting the plasma current, meeting requirements from non-

inductive techniques and confinement, MHD physics. In spite of the intention controlling a

monotonic current buildup, a non-linear interplay between the non-inductive driven and ITB-

generated BS currents exhibited a self-organized oscillation of the current profile, which

provides a favorable effect shortening the buildup time [6, 7]. The avoidance of current hole

formation and the external control of the ITB formation are also discussed.

[1] S. Nishio et al., 20th IAEA Fusion Energy Conf. (Vilamoura) FT/P1-21 (2004).

[2] S.C. Jardin, Nucl. Fusion 40 (2000) 1101.

[3] S.C. Jardin, N. Pomphery and J. Delucia, J. Comput. Phys. 66 (1986) 481.

[4] R. E. Waltz, G. D. Kerbel, J. Milovich, Phys. Plasmas 1 (1994) 2229.

[5] A. Fukuyama et al., Nucl. Fusion 40 (2000) 685.

[6] Y. Nakamura et al., 31th EPS, P2-140, London, 2004.

[7] Y. Nakamura et al., J. Plasma Fusion Res. SERIES 6 (2004) 558.


Configuration Dependence of MHD Activities in High- regime of

Large Helical Device

S.Sakakibara1, K.Y.Watanabe

1, H.Yamada

1, Y.Narushima

1, H.Funaba

1, K.Toi

1, S.Ohdachi

1,

T.Yamaguchi2, S.Inagaki

1, K.Narihara

1, K.Tanaka

1, T.Tokuzawa

1, K.Ida

1, K.Kawahata

1

and LHD Experimental Group1

1. National Institute for Fusion Science, Toki 509-5292, Japan 2. Dep. of Fusion Science, Graduate Univ. for Advanced Studies, Toki 509-5292, Japan

Characterization of pressure-driven modes and control of them in the high-d regime are one

of crucial issues towards for a helical fusion reactor. Since the heliotron configuration has

a magnetic hill in the peripheral region and weak magnetic shear in the plasma core,

violation of stability of ideal and resistive interchange modes are concerned. To

investigate configuration dependence of MHD activities, the control of rotational transform

profile has been done in high-d regime of Large Helical Device (LHD). The central

rotational transform k2/2r can be changed from 0.4 to 0.73 at the same magnetic axis

position. The increase in k2/2r leads to restraint of Shafranov shift restricting spontaneous

magnetic well formation and the reduction of magnetic shear. MHD modes excited in

peripheral region are dominantly observed and enhanced when the beta increases in any

configuration, although averaged beta exceeds 3 % in any configuration. Also, the

dependence of magnetic Reynolds number, S, on MHD modes have been found out, and

about 10 % of degradation of plasma stored energy due to peripheral MHD modes has been

observed in density ramp-up operation reducing S parameter. The linear theory suggests

that the growth rate of resistive interchange mode is increased by an increment of S

parameter, and it is qualitatively consistent with characteristics of observed MHD activities.

On the other hand, the destabilization of MHD modes due to the reduction of magnetic

shear has been observed in the experiments. When the plasma current increasing

k2/2r"exceeds"a certain value, minor collapse of the plasma due to m/n = 1/1 mode occurs.

Especially, in the configuration with high k2/2r, even small plasma current leads to large

degradation of the plasma. Then the ratio of the decrease in beta value to total one is more

than 50 %. The abrupt reduction of electron temperature in t ~ 0.5 was observed, while

peripheral plasma pressure with strong magnetic shear was maintained. The impact of

m/n = 1/1 mode on the plasma is much stronger than that of m/n = 2/1 mode destabilized by

reducing the magnetic shear due to the plasma current.


Experimental study of current driven MHD mode in LHD Y. Narushima1, S. Sakakibara1, K.Y. Watanabe1, T. Yamaguchi2, H. Yamada1, K. Ichiguchi1,

K.Narihara1, K. Ida1, S. Ohdachi1, T. Tokuzawa1, K. Tanaka1, S. Inagaki1, Y. Takeiri1

and LHD experimental Group1

W.A. COOPER3

1 National Institute for Fusion Science, Toki 509-8292, Japan 2 Dep. of Fusion Science, Graduate Univ. for Advanced Studies, Toki, Gifu 509-5292, Japan

3 CRPP Association Euratom / Confederartion Suisse, EPFL, 1015 Lausanne, Switzerland

In general, Heliotrons do not require the plasma current for sustaining the magnetic

field to confine the plasma. However, there is a possibility to flow the large plasma

current due to the unbalance of the Neutral beam injection (NBI) or Bootstrap current and

so on. These kinds of current play an important role from a viewpoint of

magnetohydrodynamics (MHD) stability because the plasma current modifies the profile

of the rotational transform angle ι/2π , which affects the characteristics of the pressure

and/or current driven MHD instabilities. To study the characteristics of the current driven

MHD instabilities in Heliotron plasma, the plasma with finite current is produced and

investigated in Large Helical Device (LHD). The plasma current driven by the two

co-NBIs makes the rotational transform higher. When the plasma current reaches a certain

value, the plasma current and stored energy drop within several hundred milliseconds.

During this minor collapse, the electron temperature profile indicates the wide flat region

around the resonant surface of ι/2π=1. In case of the higher β, the reachable plasma

current becomes lower. The reachable plasma currents are consistent with the prediction

of the low-n ideal 3-D MHD analysis code TERPSICHORE, which shows that the m/n=1/1

mode is destabilized at the higher β and/or higher plasma current and the current driving

term of the potential energy dominates the pressure driving term in the region of the

parameter of the collapsed plasma in experiment.


Reproducible Appearance of Quasi Single Helicity State in a Reversed Field

Pinch with an Appropriate Control of the Reversed Toroidal Field.

Y. Hirano, R. Paccagnella*, H. Koguchi, L. Frassinetti, H. Sakakita, S. Kiyama, Y. Yagi

Institute of Energy Technology, AIST, Tsukuba-shi, Ibaraki, Japan 305-8568

*Consorzio RFX and Istituto Gas Ionizzati del C.N.R, Corso Stati Uniti, 4, 35127 Camin

Padua, Italy

The quasi single helicity (QSH) state in a reversed field pinch (RFP) is one of the

configurations in which a relatively good confinement with less stochastic magnetic field and

the maintenance of the RFP configuration by dynamo action can be expected simultaneously.

So far the appearance of the QSH had been spontaneous and exhibited an insufficient

reproducibility. In this paper, however, the experimental conditions are described, by which a

quite good reproducibility for the QSH state is obtained in the TPE-RX RFP experiment.

In the scheme, the reversal of toroidal magnetic field is kept in a very shallow value

(almost zero) after the setting up and fast current rising phase of RFP. After a certain period

of the shallow toroidal field reversal, a m=1 and n=6 mode (m and n being the poloidal and

toroidal Fourier’s mode numbers respectively) rapidly grows and saturates before the

termination of the discharge. The growth of this mode dominates over the others and the QSH

state with m/n=1/6 is finally achieved. This QSH state is terminated by the loss of toroidal

field reversal with a certain duration period and can be sustained further, near the end of the

discharge, by applying a delayed toroidal field reversal with an appropriate trigger timing and

magnitude.

The initial rapid growth of the single dominant mode, by which the QSH state is initiated,

is compared with the linear stability and non-linear 3-D calculations. The timing of the rapid

growth of the mode seems to agree with the time when a very small positive pulse of the wall

toroidal field appears. This little positive pulse seems to trigger the growth of the dominant

single helical mode. The experimental magnetic field profile estimation shows that the QSH

state with m=1 and n=6 corresponds to the inner most core resonant mode. However, the

linear resistive code calculations based on the reconstructed profiles do not find this mode as

the dominant one. On the other hand the results of 3-D calculations shows a good agreement

with the above experimental observations, with an m=1/n=6 core resonant mode becoming

dominant after an initial relaxation phase.


Role of the m=0 magnetic perturbations in the crash phase of the

pulsed polidal current drive regime in the TPE-RX device

L. Frassinetti, Y.Yagi, H. Koguchi, Y. Hirano, H. Sakakita

National Institute of Advanced Industrial Science and Technology (AIST),

1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan

The application of the pulsed poloidal current drive (PPCD) technique in reversed field pinch (RFP)

devices reduces the magnetic stocasticity producing a regime with improved confinement properties.

However this effect is only transient in time and the improved confinement regime is suddenly

terminated. In this paper we will show a detailed study of the crash mechanism at the end of the improved

confinement regime in the RFP device TPE-RX. The end of this regime is preceded by the increase of

m=0 magnetic modes with high toroidal numbers. The toroidal position of this perturbation is well

localized and systematically corresponds to the position of the pre-existing slinky structure. The increase

of these m=0 modes, as well as the subsequent increase of all the other modes, produces the increase of

the magnetic stocasticity, reducing the magnetic barrier produced by the m=0 islands and breaking this

barrier at the slinky position. It will be shown that this hole in the m=0 magnetic barrier is the cause of the

end of the improved confinement regime.


Relaxed State of Reversed Field Pinch Equilibrium with Low Aspect Ratio

S. Shiina1, Y. Nagamine

2, Y. Osanai

2, Y. Kondoh

3, K. Kusano

4, Y. Yagi

1, H. Sugimoto

1, H. Ashida

1, K.

Saito2, M. Aizawa

2, M. Watanabe

2, H. Koguchi

1, Y. Hirano

1, H. Sakakita

1

1 National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan

2 Institute of Quantum Science, Nihon University, Chiyoda-ku, Tokyo, Japan

3 Department f Electronic Engineering, Gunma University, Kiryu, Gunma, Japan

4 Department of Material Science, Factory of Science, Hiroshima University, Hiroshima, Japan

Woltjer and Taylor have concluded that a small-scale turbulence causes a plasma to relax to

equilibrium with a relative minimum of the energy integral except the plasma pressure. In order to find

out a dynamo-free, steady-state reversed-field pinch (RFP) configuration at finite beta, the features of

the relaxed state with a minimum energy are examined for two types of RFP magnetohydrodynamic

(MHD) equilibrium with low aspect ratio, the classical and the neoclassical equilibrium. These

equilibria have the on-axis maximum longitudinal adiabatic invariant (Jmax) or ∇p∇J > 0 for the strong

paramagnetism, then improve further the energy confinement time owing to the stability of

microinstabilities, in addition to the neoclassical effects such as viscosity and bootstrap current. The

former is investigated by solving Grad-Shafranov equation for the current flux function I(ψ) based on

the equilibrium equation in orthogonal magnetic coordinate system (ψ, θ, φ), j =λB/µ0 +

(dp/dψ)(∇φ/|∇φ|2), which is predicted by the energy principle of non-ideal MHD plasma with the

losses of mass, entropy and helicity, and leads to the sufficient condition for the relaxed state. When λ =

const. j⋅⋅⋅⋅B/B2 is a widely uniform profile except the boundary region, which is supported by the

simulation study for the relaxation phenomena and the external(rf) current profile control to the relaxed

state. The latter is self-consistently solved by using IdI/dψ determined by the general MHD equation

and the profiles of flux surface averaged current <j⋅⋅⋅⋅B>. The neoclassical equilibrium does not satisfy

the condition of λ = const. The features of the relaxed state are explained by a minimum of Lyapunov

functional L, which is proposed as a condition for a minimum of energy and pressure. By specifying

the plasma pressure profile and the magnetic helicity, we can find the solutions of the relaxed

equilibrium with δL = 0. The neoclassical equilibrium has a hollow type of toroidal current profile in

the case of a relatively flat plasma pressure profile or high beta plasma, indicating that it is close to the

relaxed-equilibrium state with a high current density at the boundary. The hollow current profile

enhances significantly the magnetic shear or the plasma stability, simultaneously makes the steady-state

approach feasible because of its dominant self-induced current.


MHD Stability Analysis and Edge control of the ATRAS-RFP Plasma K.Saito1, S.Shiina, Y.Osanai, T.Namba and M.Watanabe1

1Institute of Quantum Science Nihon University, Tokyo 101-8308 Japan

The structure of internal magnetic field for the ATRAS-RFP plasma (major and minor

radii of 50, 9cm) was analyzed using radial distributions of inner magnetic field

observed on the equatorial surface by probe-array inserted into plasma. The pressure

profile is obtained with the magnetic pressure profile under the assumption of

cylindrical symmetry. The magnetic pressure has a peak on magnetic axis and decrease

monotonically toward the plasma surface, and plasma pressure has a shallow depression

and positive gradient around the axis then decrease monotonically toward the outside of

the plasma. The machine beta defined by volume averaged plasma pressure over

magnetic pressure made by external coil on the plasma surface is about thirty. This

means that RFP plasma has a high potential as D-D reactor, because strong poloidal

field produced by the plasma current confines the plasma itself and the toroidal field

made by external coil is very small compared with tokamaks. These profiles are

characteristics of RFP configuration differ from tokamak plasma. Under these

conditions, ideal MHD stabilities are analyzed for experimentally observed poloidal and

toroidal field configurations. Suydam’s condition is not satisfied all over the region

where plasma pressure gradient is negative. In this region, various modes having each

poloidal and toroidal mode numbers of m and k become unstable around the

reversal surface, especially. Almost instabilities depend on the sign of zkB , because the

resonance occurs on the magnetic surface of ( ) 0=+ θmBrkBz . Characteristics for m

number are as follows. 0=m : Broad band of k modes appear independent on sign

of k around the reversal surface where toroidal fields are small. 1=m : In case

1010 <<− k , these modes are unstable in the outer region of negative pressure gradient.

For short wave length of 10−<k , these modes become stable outer the reversal surface,

and unstable mode concentrate in the outer region of the reversal surface for 10>k

because toroidal field change sign to negative there.2≥m : Long wave length modes are

stable in the whole area of plasma and unstable short modes for 0<k concentrate

around the inside of the reversal surface and stable outside of it. On the contrary, for

0>k unstable short modes concentrate in the outer region of it because of negative of

the toroidal field also. These results are suggesting the existence of dynamo effect

which needed by the RFP field configuration sustained inductive toroidal electric field.

Edge controls for Suydam’s condition are attempted and it is satisfied in the thin layer

of the plasma surface.


Plasma flow injection into a torus chamber as a new approach to

flowing two-fluid plasma generation

M. Nagata1, T. Takamiya1, T. Kanki2, Y. Onishi1, N. Fukumoto1 and S. Masamune3 1 University of Hyogo, Himeji, Japan

2 Japan Coast Guard Academy, Kure, Japan 3 Kyoto Institute of Technology, Kyoto, Japan

The importance of plasma flow or two-fluid effect is recognized in understanding the

relaxed states of high-beta torus plasmas, current drive by coaxial helicity injection,

magnetic reconnection and plasma dynamo in fusion, laboratory and space plasmas. As a

new approach to create a flowing two-fluid plasma equilibrium, we have tried to inject

tangentially the plasma flow with spheromak-type magnetic configurations into a torus

vacuum chamber (R/a = 0.25 m/0.083 m) with an external toroidal magnetic field (TF)

coil by use of a magnetized coaxial plasma gun (MCPG). The MCPG can generate the

magnetized plasma flow (magnetic field strength B = 0.2 T, maximum ion velocity ui.max

= 30 km/s, maximum electron density ne.max = 0.8 ×1020 m-3 for the gun voltage Vg = 7 kV).

The ion flow velocity, electric field and electron density are measured by a directional

Mach probe on which two double probes are mounted. In the initial experiments, the

reversed-field pinch (RFP)-like configuration with helical magnetic structures (m = 0 and

m = 1 mixed state) was realized in the torus vessel. As reversing the direction of the TF,

the toroidal plasma current also was reversed. However, the ion flow measurement

showed that the ion flow keeps the same direction despite the reversal of the toroidal

current and the axial electric field. The ion fluid comes to flow in the opposite direction to

the electron fluid by the reversal of TF. This result suggests that not only electron but also

ion flow contributes significantly on the reversed toroidal current. In this case, the ratio of

ui to the electron flow velocity ue is estimated as ui/ue ~ 1/2. At the present experiment, the

generation of a perpendicular current due to the ion diamagnetic drift has not been

observed satisfactorily although the role of the ion flow in the driven current has emerged

by the TF reversal and the magnetized plasma injection. The ratio of this system size scale

to the ion skin depth, S* < 6 is relatively smaller as compared to large ST/CT devices, so

the two-fluid effect should become more important. The MCPG could be considered as a

useful tool to drive effectively the fast ion flow into toroidal plasmas.


Partial Stabilisation of NTMs with ECCD for standard scenarios in ITER

O. Sauter, H. Zohm†

Ecole Polytechnique Fédérale de Lausanne (EPFL)

Centre de Recherches en Physique des Plasmas (CRPP)

Association EURATOM - Confédération Suisse

CH - 1015 Lausanne, Switzerland†MPI für Plasmaphysik, D-85748 Garching, Germany, EURATOM Association

The performance of the ITER standard scenario can be reduceddue to the presence of low m/n

neoclassical tearing modes [1]. In particular the 3/2 and 2/1 modes are predicted to lead to the

main confinement degradation in ITER.

Localised electron cyclotron current drive (ECCD) is proposed to fully stabilise these modes,

however the power requirements are relatively large. The mainproblem is that during the stabil-

isation process, the island width will become smaller than thewidth of the jeccdprofile. Present

experimental results confirm the efficient stabilisation with ECCD down to an island width sim-

ilar to the jeccd characteristic width. In this paper we study the power requirements needed to

partially stabilise the NTMs to sizes such that less than a 10%reduction in the confinement

properties is expected. The required power is much lower than for full stabilisation, but it needs

to be delivered continuously. We discuss the advantages anddrawbacks of this new option, in

particular concerning the influence on the maximum Q value that can be expected. An advantage

of this new option is that the uncertainties in the predictions can be significantly reduced, since

present experiments directly apply and can be scaled up to ITER. Also, since the island width

will not be smaller than the width of thejeccd profile, power modulation is also not required

and the final saturated island width is directly determined bythe deposition width. Therefore

launchers can be optimised to reduce the characteristic current density profile width.

References

[1] Aymar R.et al, Nuclear Fus.41, 1301 (2001)


A model for the evolution of current-driven ELMs

C G Gimblett, R J Hastie and P Helander

EURATOM/UKAEA Fusion Association,

Culham Science Centre, Abingdon, Oxon OX14 3DB, U.K.

The ideal MHD `peeling' mode has long been thought to be involved in the generation

of Tokamak Edge Localised Mode (ELM) fluctuations, and the linear theory is well

established. Here we investigate an ELM model which hypothesises that peeling

modes produce a Taylor relaxation of an outer annular plasma region. The relaxation

has two effects on peeling mode stability: a) as the relaxation process proceeds

radially inwards it leaves in its wake a Taylor state, which for conventional Tokamak

ordering is simply a flattened equilibrium toroidal current density. This effect acting

in isolation would lead to an increased peeling growth rate (for conventional current

profiles the edge current density is increased); b) the formation of a (negative for

conventional current profiles) skin current at the plasma-vacuum interface which has

a counteracting stabilising effect. For a finite relaxed annulus, these two opposing

effects can balance and give a configuration that is peeling stable. To illustrate, for an

edge safety factor (qa) we can identify the peeling unstable mode numbers (from a

given range) and then find the maximal radial extent of the relaxed region (dE)

required for stability. Varying qa produces the graph shown below (dE normalised to

minor radius)

3 4 5 6 7qa

0.1

0.2

0.3

0.4

0.5

dE

It is shown that the subset of these equilibria which have an initial marginally stable

edge profile also generate (smaller) ELM widths in this way. Expanding the

governing equations gives analytic expressions for ELM widths in terms of edge

parameters. Other properties of ELMs are calculated within the model, such as the

natural (deterministic) scatter of predicted widths and mode numbers, and we

compare model predictions with a number of other experimental ELM properties.

This work was funded jointly by the United Kingdom Engineering and Physical

Sciences Research Council and by EURATOM.


0 1 2 3 4Electron density x1019m-3

0

1

2

3

4

5

6

B21

/BT x

10-4

Figure 1, Scaling of locked mode threshold with density

Locked mode thresholds on the MAST spherical tokamakD.F. Howell1, T.C. Hender1, G. Cunningham1,

R.J. La Haye2, J.T. Scoville21 Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon,

OX14 3DB, United Kingdom2 General Atomics, PO Box 85608, San Diego, CA, 92186-5608, USA

In an ideal tokamak, the equilibrium magnetic fields would be axisymmetric. Inpractice, however, the magnetic fields show small deviations from axisymmetry whichare known as error fields. It is well known that error fields with amplitudes Br/BT~10-4can induce resistive tearing modes in the plasma and these can grow and lead to non-rotating, or locked, MHD modes in the plasma. These locked modes typically lead totermination of the plasma.To reduce the effect of these error fields on the plasma, many tokamaks have installedsets of error field correction coils. These are designed to create non-axisymmetricmagnetic fields inside the machine to oppose the intrinsic error field. Recently, a set offour error field correction coils has been installed on the MAST spherical tokamak.These allow an n=1 field to be applied with any toroidal phase.Experiments to investigate the error fields on MAST have been performed. Correctionof the intrinsic error field has allowed MAST to operate in previously inaccessibleregimes. With error field correction, MAST can operate at densities over 30% lowerthan previously attained.Experiments have also been carried out tomeasure the locked mode threshold by applyinglarge error fields using the coils. In this way wehave determined how the locked modethreshold scales with density, q and toroidalfield. We found that Br/BT ~n1.1 q1.35 which issimilar to the scalings obtained fromconventional aspect ratio tokamaks.Experiments to compare these results withthose from DIII-D, which has almost the sameminor radius as MAST, are in progress and will allow the effect of aspect ratio onlocked mode thresholds to be determined.This work was partly funded by Euratom and the UK Engineering and PhysicalSciences Research Council


Stabilisation of Sawteeth in MAST by Toroidal RotationR J Akers, I T Chapman, T C Hender, G T A Huysmans*, S Saarelma, S E Sharapov and

the MAST teamUKAEA Fusion Association, Culham Science Centre, Abingdon, UK* EURATOM/CEA Cadarache, 13108 St. Paul-Lez-Durance, France

Toroidal rotation approaching the sound speed has been shown to stabilise resistive internalkink modes with mode number n=1, eliminating sawteeth [1]. Control of sawteeth is vitalfor plasma performance as large sawteeth can trigger neo-classical tearing modes that causeconfinement degradation.Sawtooth behaviour is compared in MAST plasmas with approximately matching magneticfield, flat-top current and shape. Results are consistent with previous results from JET [2]and TEXTOR [3]. It is found that as co-NBI power is increased the sawtooth period alsoincreases. However, as counter-NBI power is increased, the sawtooth period first decreasesto a minimum then subsequently lengthens (Fig. 1). Since counter-NBI causes toroidalrotation opposed to the diamagnetic frequency, ω*i, this minimum is offset from the ohmicregime. The precursor mode rotates in the same direction as the plasma current in anohmically heated plasma, and so a momentum input is required in the counter-currentdirection to stop the MHD rotation, which is given by the sum of the ion diamagneticfrequency and the rotation frequency. The data shows that the minimum of sawtooth periodis at a similar NBI power to that at which the precursor has null frequency (Fig. 2).The MISHKA-D code [4] has been used to investigate the stability of the internal kinkmode with respect to the toroidal velocity using equilibria carefully matched to theexperiment. Initial results indicate that the internal kink mode is stabilised when thetoroidal flow approaches half of the sound speed. It is found that the maximum growth rateof the mode occurs with counter toroidal velocity and is dependent upon the iondiamagnetic frequency, in accordance with experiment.

Studies are in progress to complete the quantitative comparison of the modelled effects oftoroidal flow on the internal kink with the experimental sawtooth behaviour.

[1]. RG Kleva et al, Phys. Plasmas 9 (2002) 3013[2]. MFF Nave et al, Proc. 31st EPS Conf. On Contr. Fusion and Plasma Phys. (London 2004)[3]. HR Koslowski, Fusion Sci. Tech. 47 (2005) 260[4]. GTA Huysmans et al, Phys. Plasmas 8 (2001) 4292This work was funded by Euratom and the UK Engineering and Physical Sciences Research Council

Figure 1 Figure 2

Figure 1 shows the sawtooth period and Figure 2 shows the sawtooth precursor frequency for dischargeson MAST respectively as functions of the NBI power.


Simulation of ITER Improved H-mode Operation with the Integrated Core Pedestal SOL Model Using MMM95 and GLF23 Core Transport

Models G.W. Pacher1, H.D. Pacher2, G. Janeschitz3, A.S. Kukushkin4, G. Pereverzev5, A. Pankin6,

I. Voitsekhovitch7

1 Hydro Quebec (IREQ), Canada 2 INRS, Quebec, Canada

3 FZK-PL-Fusion, Karlsruhe, Germany

4 ITER International Team, Garching, Germany 5 Max-Planck-Institut für Plasmaphysik, EURATOM Assoc., Germany

6 SAIC, San Diego, USA 7

Euratom/UKAEA Fusion Association, Abingdon, United Kingdom

ITER improved H-mode operation has recently been modelled [1] with self-consistent

parameters for the core and edge using the Integrated Core Pedestal SOL Model

(ICPS Model [2]) in the 1.5D Astra code. For those simulations, the core energy transport

was given by the MMM95 transport model [3], with a transport reduction related to the

sparseness of low-order rational surfaces for such flat-q discharges [4]. The stabilisation

parameters were adjusted to give reasonable agreement with an improved H-mode discharge

in Asdex-UG.

The simulation of improved H-modes in JET with the same model then exhibits reasonable

agreement at medium heating power. At higher heating power, however, the agreement is

not satisfactory: the simulated ion and electron temperatures remain almost equal, in contrast

to the experimental result that ion temperature was appreciably higher than electron

temperature. This appears to be due to particular characteristics of the core transport model

used (MMM95), since hot ion H-modes (without stabilisation) are also not well simulated.

The work reported here investigates the effect of using a different core transport model

(GLF23 [5]). Initial results indicate that agreement of the hot ion H-mode simulations with

experiment is then appreciably better. This transport model, including the stabilisation

mechanism due to the sparseness of rational surfaces referred to above, is validated against

JET and AUG discharges and then applied to simulations of improved H-modes for ITER.

The results for standard and improved H-modes are presented and compared with those

previously obtained.

[1] G.W. Pacher, et al., IAEA-CN-116_ITP3-25, (Proc. 20th IAEA Conf. Vilamoura, 2004) [2] G.W. Pacher, et al., Plasma Phys. Contr. Fus. 46 (2004) A257 [3] G. Bateman, A.H.Kritz et al., Phys Plasmas 5 (1998) 1793 [4] I. Voitsekhovitch, et al., Phys. Plasmas 9 (2002) 4671 [5] R.E. Waltz et al., Phys. Plasmas 4 (1997) 2482


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Biasing Experiments by a Ti Electrode in the Tohoku University Heliac

H. Utoh 1, K. Nishimura2, S. Inagaki2, H. Takahashi 1, Y. Tanaka 1, M. Takenaga 1, M. Ogawa 1, J. Shinde 1, K. Shinto 1, S. Kitajima 1, M. Sasao 1

1 Department of Quantum Science and Energy Engineering, Tohoku University, Sendai, Japan 2 National Institute for Fusion Science, Toki, Japan

In the Tohoku University Heliac (TU-

Heliac), influence of a radial electric field on

plasma parameters has been investigated by

electrode-biasing experiments. In both

positive and negative biasing experiments,

the improvement of plasma confinement is

clearly observed when the radial electric field

is formed [1-2].

In the present work, we show the first

experimental results using a Ti electrode. If

the Ti electrode is successfully storing

hydrogen, the radial electric field can be

actively varied by controlling the ion current

from the Ti electrode. In addition, high

energy particle behaviour can be simulated

by accelerated ions from the Ti electrode.

When the Ti electrode that had been!

pre-immersed in the H2 gas (p=2.7×105 Pa,

12 hour) is positively biased, the radial

distribution of the electric density slops steeply and a strong positive radial electric field is

formed, indicating the improvement of plasma confinement.

In contrast, by a negatively biased Ti electrode of similar pre-treatment, the electric

density increases rapidly in an Argon plasma. Typical time history of plasma parameters is

shown in Fig. 1. This phenomenon has not been observed by a negatively biased stainless steel

electrode.

[1] S. Inagaki et al.: Jpn. J. Appl. Phys. 36, 3697 (1997).

[2] S. Kitajima et al.: Int. J. Appl. Electromag. Mech. 13, 381 (2002).

p0 = 6.7×10-3 Pa ρE = 0.6

Working Gas : Ar

Fig. 1 Time evolutions of plasma parameters

B0 = 0.34 T


Εξτραπολατιον οφ Πλασµα Χυρρεντ Θυενχη Τιµε δυρινγ ∆ισρυπτιονσ

φροµ Εξιστινγ Μαχηινεσ το ΙΤΕΡ

Μ. Συγιηαρα1, Η. Οηωακι2,3, Ψ. Καωανο2, ς.Ε. Λυκαση4, Ρ. Κηαψρυτδινοϖ5,

Ψυ. Γριβοϖ1, Α. Ηαταψαµα3, Τ. Οζεκι2, Μ. Σηιµαδα1

1 ΙΤΕΡ Ιντερνατιοναλ Τεαµ, Νακα ϑΩΣ, Νακα−σηι, Ιβαρακι−κεν, ϑαπαν 311−01932 ϑαπαν Ατοµιχ Ενεργψ Ρεσεαρχη Ινστιτυτε, Νακα−σηι, Ιβαρακι−κεν, ϑαπαν 311−0193

3 Κειο Υνιϖερσιτψ, Ηιψοσηι, Ψοκοηαµα, ϑαπαν 223−85224 ΡΡΧ Κυρχηατοϖ Ινστιτυτε φορ Ατοµιχ Ενεργψ, Μοσχοω, Ρυσσιαν Φεδερατιον

5 ΤΡΙΝΙΤΙ, Τροιτσκ, Ρυσσιαν Φεδερατιον

Ροβυστνεσσ αγαινστ τηε ελεχτρο−µαγνετιχ (ΕΜ) λοαδ ον τηε ιν−ϖεσσελ χοµπονεντσ ανδ

ϖαχυυµ ϖεσσελ δυε το τηε εδδψ ανδ ηαλο χυρρεντσ ινδυχεδ δυρινγ τηε χυρρεντ θυενχη πηασε οφ

δισρυπτιονσ ισ εσσεντιαλ φορ τηε ΙΤΕΡ δεσιγν. Τηε µοστ χριτιχαλ λοαδσ αρε τηοσε δυε το τηε

φαστεστ χυρρεντ θυενχη ανδ, τηυσ, τηε σπεχιφιχατιον φορ τηε σηορτεστ θυενχη τιµε ιν ΙΤΕΡ µυστ

βε προϖιδεδ βασεδ ον εξπεριµενταλ δατα φροµ εξιστινγ µαχηινεσ ανδ ον τηεορετιχαλ στυδιεσ οφ

τηε δατα ωιτη σοπηιστιχατεδ νυµεριχαλ χοδεσ.

Τηε ρατιο οφ τηε χυρρεντ θυενχη τιµε τ οφ ΙΤΕΡ το τηατ οφ αν εξιστινγ µαχηινε χαν βε

εξπρεσσεδ χονϖενιεντλψ βψ Εθ. (1). Ηερε Σ ισ τηε

πολοιδαλ χροσσ σεχτιον αρεα οφ τηε πλασµα βεφορε

ττ

ηη

ΙΤΕΡ

ΕΞΠ

ΕΞΠ

ΙΤΕΡ

ΙΤΕΡ

ΕΞΠ

εφφ

ΙΤΕΡ

εφφ

ΕΞΠ

Σ

Σ

Λ

Λ≈

( )( ) (1)

δισρυπτιονσ, η ισ τηε πλασµα ρεσιστιϖιτψ ανδ Λεφφ ισ τηε εφφεχτιϖε πλασµα ινδυχτανχε. Τηε

σιµπλεστ ωαψ το εξτραπολατε τηε θυενχη τιµε το ΙΤΕΡ ισ το υσε ονλψ τ/Σ. Αλτηουγη

εξαµινατιονσ οφ τηε δισρυπτιον δαταβασε ωιτη τ/Σ προϖιδεσ αππροξιµατε πρεδιχτιον φορ τηε

θυενχη τιµε ιν ΙΤΕΡ [1], τηε εφφεχτ οφ τηε συρρουνδινγ χονδυχτινγ στρυχτυρε ον Λεφφ ανδ τηε

διφφερενχε ιν τηε ϖαριατιον οφ τηε χροσσ σεχτιον αρεα δυρινγ δισρυπτιονσ βετωεεν εξιστινγ

µαχηινεσ ανδ ΙΤΕΡ αρε νοτ προπερλψ τακεν ιντο αχχουντ.

Ιν τηισ παπερ, ωε υσε τηε δισρυπτιον σιµυλατιον χοδε βασεδ ον ∆ΙΝΑ [2] το χαλχυλατε

αν εϖολυτιον οφ τηε εθυιλιβριυµ, ωηιχη προϖιδεσ Σ ανδ Λεφφ αχχυρατελψ βοτη ιν εξιστινγ

µαχηινεσ ανδ ΙΤΕΡ. Ωε τηεν χουπλε τηε ∆ΙΝΑ χοδε ωιτη τηε τιµε δεπενδεντ χοδε φορ

ιµπυριτψ ρατε εθυατιονσ το εϖαλυατε τηε ιµπυριτψ ραδιατιον ανδ πλασµα ρεσιστιϖιτψ, ωηιχη ισ α

ρεµαινινγ ιµπορταντ παραµετερ ιν εξτραπολατινγ τηε θυενχη τιµε το ΙΤΕΡ. Ωιτη τηε νεωλψ

δεϖελοπεδ µοδελ, ωε πρεδιχτ τηε σηορτεστ θυενχη τιµε εξπεχτεδ ιν ΙΤΕΡ βασεδ ον

εξαµινατιονσ οφ φαστεστ δισρυπτιον σηοτσ οβσερϖεδ ιν τηε εξιστινγ µαχηινεσ, ε.γ., ϑΤ−60Υ.

[1] Μ. Συγιηαρα, ετ αλ., Προχ. 20τη ΙΑΕΑ ΦΕΧ, ςιλαµουρα (2004) ΙΤ/Π3−29.

[2] Ρ.Ρ.Κηαψρυτδινοϖ, ς.Ε.Λυκαση, ϑ.Χοµπυτ.Πηψσ., 109 (1993) 193.


Characteristics of Runaway Plasmas in JT-60U

Y. Kawano, T. Nakano, A. Isayama, H. Tamai, T. Kondoh, T. Hatae,

H. Kubo, N. Asakura, H. Takenaga, S. Ide

Japan Atomic Energy Research Institute

801-1 Mukoyama, Naka, Ibaraki, 311-0193, Japan

Relativistic high-energy runaway electrons can be generated during a tokamak disruption.

Since runaway electrons have the potential to damage the plasma facing components,

disruption mitigation techniques to avoid the generation of runaway electrons have been

developing for ITER. Besides those techniques, it is also essential to establish ways of

mitigating and/or terminating of the runaway electrons after their generation within

appropriate time scales with good controllability. There, behavior of runaway plasmas

must be understood well.

In JT-60U, characteristics of the post-disruption runaway plasmas have been investigated

with external actuators such as impurity ice pellet injection, neutral gas injection, and RF

injection. Runaway plasmas with current of ~0.4 MA were created as the target of the

experiment by intentional disruptions induced by the killer pellet injection. In the

experiment with the impurity (neon) ice pellet injection into the runaway plasma, we found

that the runaway electrons were exhausted by the pellet injection. An analysis suggested

that the decay time of runaway current (1 ~ 3 s) can be explained by balance of avalanche

generation of runaway electrons and their damping due to combined effects of pitch-angle

scattering and synchrotron radiation. In the experiment with the intense gas (hydrogen)

injection, we discovered a nearly runaway-only discharge without appearance of large

instabilities. At this new discharge state, we also confirmed the decay of runaway current.

Since stopping of runaway electrons by neutral gases seems effective, termination of runway

electrons by neutral gases (especially high Z noble gases) has been proposed.

On the other hand, we have newly proposed an active and direct diagnostic concept of

runaway electrons by the laser inverse Compton scattering in order to understand the

dynamics of runaway electrons. For instance, in case of head-on collision of relativistic

electrons and YAG laser photons (l=1.06 mm), expected energy of scattered photons is

ranged between 1.8 keV ~ 45 keV for the runway electron energy of 10 MeV ~ 50 MeV.

Energy and spatial distributions of runaway electrons can be known by measurement of the

scattered X-rays. The diagnostics development is now in progress.


Burn control study using burning plasma simulation experiments in JT-60U

Y. Miura1, H. Takenaga1, H. Kubo1, Y. Sakamoto1, H. Hiratsuka1, H. Ichige1, I. Yonekawa1,

Y. Kawamata1, S. Tsuji-Iio2, R. Sakamoto3, S. Kobayashi4

1 Japan Atomic Energy Research Institute, Naka, Ibaraki 311-0193, Japan

2 Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8550, Japan

3 National Institute for Fusion Science, Oroshi-cho, Toki, Gifu 509-5292, Japan

4 Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan

Burning plasma simulation experiments are performed for a burn control study in

JT-60U plasmas with and without the internal transport barrier (ITB). In burning plasmas,

plasma pressure and heating power are strongly linked through ! particle heating. This

strong linkage could easily cause a change of the fusion output without burn control. It is

important to develop a burn control method by breaking this linkage. In order to simulate

this linkage in present non-burning plasmas, a burning plasma simulation scheme has been

developed in JT-60U. In this scheme, two NB groups are used, where one simulates !

particle heating and the other simulates external heating. For ! heating simulation, the

heating power proportional to the DD neutron flux is injected. In this scheme, the

dependence of DT fusion reaction rate on ion temperature and DT density ratio is not

considered. Only the linkage of the plasma pressure and the heating power is simulated.

Since beam-thermal neutron yield gives a large contribution to the total DD neutron flux, the

linkage becomes stronger than that in the real DD burning plasma, where thermal-thermal

neutron flux is dominant. The neutron flux and the stored energy increase without burn

control in the plasmas both with and without ITB. In the ITB plasmas, disruption occurs due

to increase in the stored energy. With burn control, where the stored energy is controlled at a

constant value by a feedback control system using the external heating, the neutron flux is

kept at a constant value in the plasmas without ITB. Zero dimensional calculation shows that

the loop of increases in neutron flux and simulated ! particle heating triggered by increased

gain well simulates the loop triggered by increasing confinement.

This work was partly supported by JSPS, Grant-in-Aid for Scientific Research (A) No.

16206093.


Edge Transpor t Bar r ier Formation and Power Threshold Proper ties in

CHS

T. Akiyama1, S. Okamura

1, T. Minami

1, T. Oishi

2, A. Fujisawa

1, M. Isobe

1, K. Matsuoka

1,

S. Nishimura1, C. Suzuki

1, K. Nagaoka

1, Y. Yoshimura

1, C. Takahashi

1, M. Yoshinuma

1,

S. Kado2, H. Iguchi

1, K. Nakamura

1, K. Toi

1, M. Takeuchi

1, A. Shimizu

1, K. Ida

1, K.

Kawahata1, S. Tsuji-Iio

3, CHS experimental group

1 National Institute for Fusion Science, Toki 509-5292, Japan 2The University of Tokyo, Tokyo 113-8656, Japan

3Tokyo Institute of Technology, Tokyo 152-8550, Japan

The edge transport barrier (ETB) is observed in the Compact Helical System (CHS). We

present dependence of power threshold on plasma parameters and magnetic configurations

and the related confinement improvement in this paper.

Following injection of neutral beams, spontaneous sharp drops in Hc emission signals are

observed. The electron density gradient near the plasma edge becomes steeper while the

electron temperature profile keeps almost constant before and after a transition. These

phenomena indicate improvement in edge particle transport. The transitions occur with the

time delay in the range between 5 and 80 ms after neutral beam injections. The closer to the

threshold the input heating power is, the longer the delay time becomes and the slower the Hc

emissions decrease. After a transition the edge electron density increases and the stored

energy increases by 40%. Based on the ISS04 scaling, which is a new stellarator confinement

scaling, the energy confinement is improved by 20%.

From a parametric scan the power threshold was found to increase with increasing

electron density. The transition was not observed for the line averaged electron density of less

than 1 × 1019

m-3

. The threshold also increased with increasing the magnetic field strength. In

addition the dependences on the magnetic field configurations such as the position of the

magnetic axis and the quadrupole magnetic component were confirmed. These features in the

threshold in CHS are similar to those in tokamak H-mode. The different characteristics from

those in tokamaks so far are as follows. The threshold power in CHS is about twice larger

than the tokamak threshold scaling. The edge electron temperature is several tens eV and the

edge region is in largely collisional regime.


Combined DINA-CH and CRONOS Simulations of ITER

V.E. Lukash4, J-F. Artaud2, V. Basiuk2, V. Dokuka3, R.R. Khayrutdinov3,

S.H.Kim, J.B. Lister

Centre de Recherches en Physique des Plasmas,

Association EURATOM-Confédération Suisse, EPFL, 1015 Lausanne, Switzerland2CEA-Cadarache, France

3TRINITI, Moscow Region, Russia4RRC Kurchatov, Moscow, Russia

Simulating the Free Boundary evolution of ITER “hybrid” scenarios is a multiple challenge

which is now being met. Previously, the most advanced core transport modelling in

CRONOS had not been linked with a Free Boundary evolution code, but only functioned

with a prescribed evolution boundary code. On the other hand, the DINA-CH simulations of

ITER used relatively simple ad hoc modelling of core transport and all the effort was

dedicated to modelling Free Boundary issues, mainly plasma equilibrium control and

disruptions.

These two tools have now been combined to develop an integrated platform bridging this

gap. The intention is to provide a tool with the flexibility of operating in both previous

conditions as well as combined. The first steps in this direction were only recently completed

to demonstrate the technical solution and first scientific results are expected soon.

This paper will present and explain the approaches taken to combine these two models and

will illustrate the graphical programming environment in which this work is being

performed.

The milestones fixed for this work should allow us to present a full simulation of the ITER

“hybrid” scenario including equilibrium control and CRONOS modelling. Simulations of the

standard ITER scenarios will also be presented as an intermediate step.


Free Boundary Simulations of ITER Scenarios

V.N. Dokuka1, J-Y. Favez, R.R. Khayrutdinov1, S.H. Kim, J.B. Lister, V.E. Lukash2

Centre de Recherches en Physique des Plasmas,

Association EURATOM-Confédération Suisse, EPFL, 1015 Lausanne, Switzerland1TRINITI, Moscow Region, Russia

2RRC Kurchatov, Moscow, Russia

The DINA-CH free boundary evolution code is continually being enhanced for simulating

the ITER tokamak. Recent additions which will be presented in this paper include a

calculation of the AC losses in the superconducting magnets and an estimate of the n=0

forces on the vacuum vessel. More of the data used in the DINA-CH modelling is being

converted to the open XML format, to encourage data sharing as part of several independent

integrated modelling initiatives.

The absence of halo current modelling in the present DINA-CH version does not allow us to

simulate the final current quench in a disruption. However, it allows us to examine the VDE

part of the evolution of the plasma shape and position following a loss of control, up to the

thermal quench on contact with the vessel. Different control strategies will be presented,

evaluating their effect on both the AC losses and the n=0 vessel forces, to be applied once

loss of control has been formally identified by estimation of the unstable state of the

linearised plasma response.

Different current, shape and position controllers are being examined for their robustness in

the non-linear simulations, by varying the equilibrium profiles and testing the controllability.

This work is aimed at developing controllers which are capable of handling a wider range of

equilibria, including the reversed shear “hybrid” scenarios discussed in a companion paper.


Fast bolometry on the CASTOR tokamak

E. Dufkova1, V. Weinzettl1, D. Sarychev2, M. Kocan3

1 Institute of Plasma Physics, Prague, Czech Republic 2 RRC "Kurchatov Institute", Moscow, Russia

3 FMFI UK, Bratislava, Slovakia

A new fast bolometric diagnostic tool based on an array of AXUV diodes was installed

on the small-size CASTOR tokamak (L-mode, 30 ms pulse length, 30 kW ohmic heating).

The set with temporal resolution of 1 µs and spatial resolution about 12 mm allows

monitoring of total radiated power and consequently to observe fast changes of radiation

profile and its relaxation. Additionally, turbulent structures in the edge plasma region, in

correspondence with Langmuir probes measurements [1], are identified.

The AXUV array is placed inside the bottom diagnostic port that gives the horizontal

distribution of radiated power. The poloidal reconstruction of the radiation profile can be

computed using the asymmetrical Abel inversion [2] at each time step of 1 µs length. This

method assumes the radial symmetry broken in the horizontal direction. The different fitting

methods for the experimental data approximation are introduced. The estimation of the

plasma radiation center, FWHM and their temporal behaviour is demonstrated on shots with

different plasma position and with edge plasma biasing. Fast transitions from centric to

hollow profiles and slow relaxations back to the stable configuration are shown.

Radiation from the edge plasma region is influenced by turbulent events. Turbulent

structures can be detected due to their typical size about 1 cm comparable with spatial

resolution of bolometers. They become visible by the subtraction of the mean value from the

bolometric signal. Events are not smoothed by chord integration thanks to the small size of

CASTOR tokamak plasma. Their lifetime is 10-40 µs and propagation velocity about 2 km/s

typically. Turbulent structures observed bolometrically are also analysed using statistical

tools (correlation analysis, multifractal analysis).

References:

[1] P. Devynck, et al., Spatially resolved characterization of electrostatic fluctuations in the

scrape-off layer of the CASTOR tokamak, Plasma Phys. Control. Fusion 47 (2005) 269–280

[2] Y.Yasumoto, et al., A New Numerical Method for Asymmetrical Abel Inversion, IEEE

Transactions on Plasma Science, Vol. PS-9, No.1, March 1981


Temporally and spatially resolved measurements of VUV lines intensity

in the CASTOR tokamak

V. Piffl1, V. Weinzettl1, A. Burdakov2, S. Polosatkin2 1Institute of Plasma Physics, Association EUROATOM-IPP.CR,

Za Slovankou 3, 182 21 Prague 8, Czech Republic 2Budker Institute of Nuclear Physics, Novosibirsk, Russia

The time and spatial evolution of the light impurities emission is investigated by VUV

imaging spectrometer on plasma periphery in the CASTOR tokamak.

The imaging VUV Seya-Namioka spectrometer equipped with a spherical diffraction grating

and a two-dimensional imaging system permits a radial monitoring of radial profile of the

chord-integrated intensity of selected lines in 50-200 nm wavelength range. The fast CCD

camera reaches 1 kHz frame rate. The installed VUV spectrometer could be tilted, shot-by-

shot, for the reconstruction of line intensity radial profiles in the almost whole plasma cross-

section of 140 mm in diameter.

There is a unique situation at CASTOR experiment now, using the spectroscopy imaging

technique together with Langmuir probe measurements make possible to investigate the

influence of the applied biasing potential and biasing electrode position on plasma

confinement in broader relationships.

The measurements of the time behaviour of radial profile of the chord integrated line

intensity are mostly performed in the spectral range of 90-130 nm. In a fixed tilting position

of the spectrometer, the imaging of Lyc H I (121.6 nm), C III (97.7 nm and 117.3 nm), N V

(123.8 nm), and O VI (103.2 nm, 103.7 nm) emission is created and analysed.

The radial intensity profiles of the observed lines indicate the sensitivity to the two different

confinement regimes in OH discharges: standard regime without biasing and regime with an

improved confinement by edge plasma biasing. It provides the experimental data for

quantifying the influence of the transport phenomena on ionisation equilibrium of the light

impurities in CASTOR experimental conditions.

Acknowledgement: This work is supported by the Academy of Science of the Czech

Republic, Grant K 204 31 05.


Progress in evaluation of radiation-hard galvanomagnetic devices

for use in the ITER magnetic diagnostic

I. Duran1, M. Hron

1, J. Stöckel

1, L. Viererbl

2, I. Bolshakova

3, R. Holyaka

3, V. Erashok

3,

P. J. Moreau4, F. Saint Laurent

4, J. P. Gunn

4

1 Institute of Plasma Physics, Association EURATOM/IPP.CR, Za Slovankou 3,

18200 Praha 8, Czech Republic

2 Nuclear Research Institute plc, 25068 Husinec-Rez 130, Czech Republic

3 Lviv Polytechnic National University, Kotliarevsky St. 1, 79013 Lviv, Ukraine

4 Association Euratom/CEA sur la fusion controlèe, Saint Paul Lez Durance, France

Use of various configurations of flux loops for measurement of magnetic field in fusion

devices is inherently limited by the pulsed operation of these machines. A principally new

diagnostic method must be developed for magnetic measurements in true steady state

regime of operation of fusion reactor. One of the options is the use of diagnostics based on

Hall sensors. This technique is well established for many applications in experimental

physics as well as industry, although it is rarely implemented in the experimental plasma

physics. The use of Hall sensors in ITER is presently limited by their questionable radiation

and thermal stability, as well as by a little experience with their performance in tokamak

environment. Issues of reliable operation in ITER-like radiation and thermal environment

will be addressed in the presentation.

The results of irradiation tests of candidate Hall sensors in LVR-15 experimental fission

reactor will be reviewed. Degradation of the best sensor’s sensitivity by 10% was observed

after neutron irradiation by the total neutron fluence of 2·1017

n/cm2. This level of neutron

fluence is comparable to that expected to occur over the whole ITER life time for a sensor

location just outside the ITER vessel. A possible in-situ recalibration technique will be

suggested to correct for deterioration of the sensor’s performance during its long-term

operation in ITER-like radiation environment.

The performance of a 3D Hall probe was recently tested on Tore Supra tokamak taking

advantage of its long pulse capabilities. The probe head was installed onto the poloidal field

coil outside the Tore Supra vacuum vessel. Perfect agreement with a low-drift 3D magnetic

coil set placed in a similar location was achieved. Additional experiments with a full

poloidal ring of Hall probes is in the final stage of preparations on CASTOR tokamak and

the first results will be presented.


Li-beam developments

G. Anda1, S. Bató1, G. Petravich1, S. Zoletnik1, R. Uhlemann2

1 KFKI-Research Institute for Particle and Nuclear Physics, EURATOM Association

POB.49., H-1525 Budapest, Hungary2 Forschungszentrum Jülich GmbH, IPP, Associaton EURATOM, Jülich, Germany

Energetic (few 10 keV) Li atom beams are routinely used to measure various parameters of

magnetically confined fusion plasmas. The Li atoms are excited in the plasma and the excited

states decay with the emission of a photon of characteristic wavelength (lambda = 670.8nm).

Measuring the intensity of this resonance line one can determine the plasma density and its

fluctuation along the beam path. Measurement of the line shape gives information on the mag-

netic field in the observation volume. Charge exchange with plasma impurity ions gives the

possibility of the determination of impurity ion concentrations.

All of the above diagnostic applications require high beam current, some well above the

presently available 1-2 mA. Recently new emitter material was found to be capable of deliv-

ering substantially higher ion currents than the conventionally used B-eucriptit and spodumen

sources. This new ion source was first investigated at KFKI-RMKI in an ion extraction geom-

etry developed specifically for this purpose and then successfully tested in the JET duplicate

Li-beam at IPP-Garching.

The beam of the TEXTOR Li-gun has been tested at KFKI-RMKI, Budapest to find optimal

operational conditions and limits. During these tests the current distribution of the beam was

measured at three locations along the beam path using a novel method. These test results have

been used to validate calculations made with the AXCEL code, and for exploring possible

improvements in the ion optics.

In this contribution the new thermionic ion source with the recently developed new extractor-

ion optic geometry and the TEXTOR Li-beam are investigated.


Investigation of pellet-plasma interaction on ASDEX Upgrade

S. Kálvin1, É. Belonohy1, K. Gál1, G. Kocsis1, P.T. Lang2, G. Veres1,

ASDEX Upgrade Team

1 KFKI–Research Institute for Particle and Nuclear Physics,EURATOM Association, P.O.Box

49, H–1525 Budapest–114, HUNGARY2Max–Planck–Insitut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, 85748

Garching, GERMANY

In order to get deeper insight into the physics of pellet-plasma interaction detailed theoretical

studies are required. To check the theoretical models observation of the ablation cloud with high

spatio-temporal resolution is sorely needed.

Recently cryogenic hydrogen isotope pellets were used not only for tailoring the core profile

but also for edge plasma control by means of frequent small and shallow penetrating pellets. For

this ELM (Edge Localised Mode) control investigations the understanding of the underlying

processes depends highly on the information regarding the localisation of the pellet at the ELM

onset, the 3D distribution of the pellet cloud and the mass deposition profiles determining the

local perturbation of the plasma. High resolution ablationprofiles and pellet path measurement

at different pellet parameters (mass and velocity) could help understand the mechanism of the

ELM triggering.

To detect the spatial distribution and time evolution of thevisible radiation emitted during

pellet ablation in ASDEX Upgrade plasmas an observation system was developed. The setup

consists of fast, triggerable digital cameras that detect the pellet cloud distribution with 12 bit

dynamic range and photodiodes that measure the time evolution of the light emission. Tangen-

tial, vertical and horizontal views of the inboard pellet injection at ASDEX Upgrade provide

3D information. The great variety of possible combinationsof different images, timings and

wavelength selections makes the detection sophisticated.Combination of triggered fast camera

images and photodiode signals enables us to localise the pellet cloud at a certain time, as well.

The time resolution of the system (both cameras and photodiodes) is 1µs.

The pellet cloud properties, like its radiation distribution and dynamics were investigated for

different pellet and plasma parameters with particular attention to the pellet ELM triggering.

The results of these investigations are the subject of the present contribution.


Effect of ion-neutral collision on the deduction of plasma flow velocity

K.-S. Chung, Y.-S. Choi, M.-J. Lee and H.-J. Woo

electric Probe Applications Lab., Hanyang University

17 Haengdang, Seongdong, Seoul 133-791, Korea

A fluid theory on the ion collection has been developed for the deduction of plasma flow

velocity in unmagnetized plasmas with high collisionality of neutrals and ions, which are to

be applicable to the deduction of ExB shear flow in divertor private region of fusion devices

and deduction of flow velocity in space and processing plasmas. Experimental application of

this method to the collisional, weakly collisional, collisionless plasmas, are given by

measuring plasma flows in various unmagnetized plasmas in Hanbit magnetic mirror device,

a dc plasma torch, a rf plasma. The measured data have been analyzed by using collisionless

kinetic theory and PIC code simulation for unmagnetized plasmas and compared with those

by collisional model. Applicable range of these theories will be reviewed and the measured

Mach probe data will be reanalyzed by considering collisional and low ion temperature

effects. Application to the deduction of ExB shear velocity in the private region of divertor

will be addressed.


Integrator for the KSTAR magnetic diagnostics

J. G. Bak1, S.G. Lee1, Derac Son2

1 Korea Basic Science Institute, Taejeon, KOREA2 Hannam University, Taejeon, KOREA

An analogue integrator has been developed for the field measurement during a plasma

discharge (with the pulse length of up to 300s) by using inductive magnetic sensors that will be

installed in the KSTAR machine. The integrator, which automatically compensates a drift, can

be controlled by a PC through the RS-232 interface. The drift is compensated by the ADC-

register-DAC in the integrator, which is improved from the technical data in the drift

measurement by using a previous integrator. In addition, the digital integrated data can be

obtained from the integrator, which will be used for a real-time monitoring of the integrated

signal. The prototype integrator was fabricated and its characteristics were investigated from

the performance test. The calibration of the integrator was carried out before each test in order

to minimize the drift. The experimental results of the integrator for the KSTAR magnetic

diagnostics obtained from the performance test are presented.


Fabr ication details for the KSTAR magnetic diagnostics

S. G. Lee and J. G. Bak

Korea Basic Science Institute, Taejeon, KOREA

The engineering design of magnetic diagnostics for the initial operation of KSTAR tokamak

has been completed. Many samples for the magnetic diagnostics include a Rogowski coil,

flux/voltage loop, saddle loop, magnetic field pick-up probes, and so on have been successfully

fabricated. Performance tests of the fabricated samples were carried out in a magnetic

diagnostics test chamber and installation exercises were simulated in a magnetic diagnostics

installation chamber, which is similar size with the KSTAR in-vessel vacuum chamber.

Recently, the final products of the Rogowski coils and magnetic field pick-up probes were

fabricated. Proper combined MgO cables are selected for the flux/voltage loop, saddle loop and

locked-mode coil. The fabrication details of the final products for the KSTAR magnetic

diagnostics, installation exercise and performance test results of the fabricated samples are

presented.


A new probe for ion temperature measurements in the tokamak

scrape-off layer

M. Ko7an1, R. Pánek

2, J.P. Gunn

3, J. Stöckel

2, J. D. Skalný

1

1 Department of Experimental Physics, Comenius University, Bratislava, Slovakia

2 Institute of Plasma Physics, Czech Academy of Sciences, Prague, Czech Republic

3 CEA Cadarache, 13108 Saint Paul Lez Durance, France

We present particle-in-cell simulations of a new kind of robust Langmuir probe for fast

ion temperature measurements in the tokamak scrape-off-layer (SOL). This probe, the

so-called segmented tunnel probe (STP), has been recently built and successfully tested

in the CASTOR tokamak. It consists of a hollow conducting tunnel, closed at one end

by an electrically isolated conducting back plate, with the tunnel axis parallel to the

magnetic field. To repel electrons, both conductors are negatively biased. Ions that flow

into the orifice are diverted onto tunnel surface by the intense radial electric field in the

magnetic sheath. The distribution of ion flux onto the tunnel decays with a characteristic

length scale that is determined by the relative straight of the radial acceleration with

respect to the incident parallel ion velocity. The latter is a function of the ion

temperature. Therefore, by dividing the tunnel into the two segments, the ion

temperature can be found from the ratio of ion current to the first and the second

segment.

The numerical simulations (XOOPIC code) are used for the probe calibration and

interpretation of the experimental data. We show that the STP is able to measure the ion

temperature in SOL and we present preliminary radial profiles of ion temperature in

CASTOR tokamak using calibrations obtained from PIC simulations. We also study the

optimization of the probe performance by the means of the PIC simulations as well as

the influence of the secondary electron emission from the probe on the interpretation of

experimental data.


Fluctuation measurements by reflectometry in the stellarator TJ-II

T. Estrada1, E. Blanco1, L. Cupido2, M.E. Manso2 and J. Sánchez1

1Laboratorio Nacional de Fusión, Asociación Euratom-CIEMAT, 28040 Madrid, Spain

2Associação Euratom-IST, CFN, Instituto Superior Técnico, 1096 Lisboa, Portugal

A broadband fast hopping reflectometer designed for measuring plasma turbulence has been

recently installed in TJ-II. The main feature of the reflectometer is its possibility to be tuned,

within a fraction of a millisecond, to any selected frequency keeping synchronized the Local

and Radiofrequency oscillators with the same stability as a fixed frequency system would do.

This property enables to probe several plasma layers within a short time interval during the

discharge, permitting the characterization of the radial distribution of plasma fluctuations. To

allow fast frequency hopping the reflectometer incorporates a fast frequency synthesizer at

microwave frequencies 8 - 12.5 GHz multiplied into the mm-wave range 32 - 50 GHz. The

system includes a harmonic mixer for heterodyne detection with sensitive phase and

amplitude measurements. A description of the system can be found in Ref [1].

As in many other experiments, the spectra of the reflectometer signal are often asymmetric.

This asymmetry is a sign of poloidally propagating plasma fluctuations and although no

quantitative results of rotation velocity can be obtained with the present reflectometer

arrangement, qualitative results have turned out to be very useful. Reflectometry

measurements have permitted the characterization of the velocity shear layer that develops

spontaneously in the edge of TJ-II plasmas above a certain critical density [2].

Simultaneously, a second velocity shear layer develops at inner radial locations (!!0.8), that

moves inwards when the plasma density further increases. Experimentally it is also observed

that this critical density depends on the heating conditions and magnetic configuration.

Besides, the reflectometer signals allow the radial localization of coherent modes that appear

in some magnetic configurations and often the determination of their propagation direction.

The interpretation of these experimental results has been crosschecked with results obtained

using a two-dimensional full-wave code [3]. In addition, the comparison with results

obtained using Langmuir probes and a high-speed imaging system ensures the correct

interpretation of the results.

[1] L. Cupido, J. Sánchez and T. Estrada. Rev. Sci. Instrum 75 (2004) 3865

[2] C. Hidalgo, M.A. Pedrosa, L. García and A. Ware. Phys. Rev. E 70 (2004) 067402

[3] E. Blanco, S. Heuraux, T. Estrada, J. Sánchez and L. Cupido. Rev. Sci. Intrum 75 (2004) 3822


Self-consistent modelling of supersonic He beam attenuation in the

TJ-II Edge Plasmas.

A. Hidalgo, F.L. Tabarés, D. Tafalla and B. Brañas

Laboratorio Nacional de Fusión. As. EURATOM/Ciemat, Madrid. Spain.

Atomic beams represent an excellent tool for the parametric characterization of the plasma

periphery in fusion devices. In particular, the use of supersonic He beams, even with

average velocities in the thermal range, allows for the sampling of a significant part of the

edge/SOL region due to the high ionisation potential of the injected atoms. Furthermore,

the low divergence and narrow velocity distribution of this type of beams strongly

simplifies the interpretation of the data. In the TJ-II stellarator one of these sources has

been installed and it is used as a routine diagnostic for the electron temperature and

density profile reconstruction, based on the line ratio method [1]. Typical values of

2<ne<10 (101 2 cm-3) and 20<Te<100 (eV) are deduced for ECRH plasmas, in reasonable

agreement with other diagnostics. Due to the good optical access, the full penetration of

the beam into the plasma can be typically monitored, thus allowing for the concomitant test

of the hypothesis made in the profile reconstruction, that are encompassed into the

collisional-radiative model. In the present work, the matching between the reconstructed ne

and Te profiles and the associated penetration of the beam is tested. A systematic lower-

than-expected penetration, which is approximately 4cm, is experimentally observed. The

same outcome has been reported by other groups [2]. Based on that, a critical analysis of

the collisional processes involved in the beam attenuation is made, with particular attention

paid to the possible effect of elastic collisions, likely dominated by the plasma ions.

[1] A. Hidalgo et al. Rev. Sci. Instrum. 75 (2004) 3478 and references therein.

[2] B. Schweer, M. Brix and M. Lehnen. J.Nucl. Mater. 266-269 (1999) 673.


F e a s i b i l i t y s t u d y f o r a b l o w o f f t e c h n i q u e t o r e a l t i m e m o n i t o r d u s tp a r t i c l e s i n f u s i o n p l a s m a sB . Z u r r o , D . J i m é n e z , A . B a c i e r o , M . A . O c h a n d o , K . J . M c C a r t h y , F . M e d i n a a n d A . L ó p e zL a b o r a t o r i o N a c i o n a l d e F u s i ó n p o r C o n f i n a m i e n t o M a g n é t i c o . A s o c i a c i ó n E U R A T O M /C I E M A T p a r a F u s i ó n . M a d r i d . S p a i nA b s t r a c tO n e o f t h e m o s t c h a l l e n g i n g d i a g n o s t i c p r o b l e m s t o b e s t i l l s o l v e d i n f u s i o n p l a s m a s i s t h er e a l c t i m e d e t e c t i o n o f d u s t p a r t i c l e s , w h o s e i m p o r t a n c e a n d i m p a c t f o r I T E R h a v e b e e na m p l y r e c o g n i z e d ( 1 ) . T h e i m p a c t o f d u s t p a r t i c l e o n t h e p e r f o r m a n c e o f c u r r e n t f u s i o nd e v i c e s i s s t i l l n o t a d e q u a t e l y u n d e r s t o o d , t h i s b e i n g l a r g e l y d u e t o t h e l a c k o f a m e t h o d t od e t e c t t h e i r p r e s e n c e a n d q u a n t i f y t h e i r p r o p e r t i e s . A l t h o u g h a l o t o f i n f o r m a t i o n h a s b e e ng a t h e r e d o n r e s i d u a l d u s t c o l l e c t e d a f t e r m a n y m o n t h s o f p l a s m a o p e r a t i o n ( 2 ) , s u c h p a r t i c l e sc a n n o t b e t r a c k e d d u r i n g p l a s m a o p e r a t i o n , e x c e p t a t t h e p l a s m a p e r i p h e r y ( 3 ) .T h e m e t h o d p r o p o s e d h e r e c o n s i s t o f b u r n i n g t h o s e d u s t p a r t i c l e s l i e a l o n g t h e p a t h o f ap u l s e d l a s e r b e a m a n d d e t e c t i n g i n r e a l c t i m e t h e r e s u l t a n t e m i s s i o n o f t h e h o t d u s t p a r t i c l e su s i n g a p h o t o m u l t i p l i e r a n d a p p r o p r i a t e f i l t e r . S i n c e t h e l a s e r p o w e r n e e d e d f o r t h i s c a n b ea c h i e v e d w i t h c o m m e r c i a l l y a v a i l a b l e s y s t e m s , a n d w i t h r e p e t i t i o n r a t e s o f 1 0 c 1 0 0 H z , t h em e t h o d s e e m s t o h a v e t h e a p p r o p r i a t e d t i m e a n d s p a t i a l r e s o l u t i o n t o h a v e a n a t t r a c t i v ep r o j e c t i o n t o t h i s g o a l .T h e m e t h o d o u t l i n e d a r o s e f r o m e x p e r i m e n t s c o n d u c t e d t o a c h i e v e a b e t t e r u n d e r s t a n d i n g o ft h e l a s e r a b l a t i o n t e c h n i q u e u s e d f o r i n j e c t i n g i m p u r i t i e s i n t o t h e T J c I I s t e l l a r a t o r , a n dt h e r e f o r e i t i s i n t e n d e d t o u s e t h e s a m e e x p e r i m e n t a l s e t u p t o s t u d y t h e f e a s i b i l i t y o f t h i st e c h n i q u e . A l o g o f d u s t p a r t i c l e s e n t e r i n g T J c I I p l a s m a s , i d e n t i f i e d b y V U V s p e c t r o s c o p y ,h a s b e e n k e p t d u r i n g r e c e n t e x p e r i m e n t a l c a m p a i g n s . A s t u d y o f t h e e x p e r i m e n t a l c o n d i t i o n sw i l l h e l p t o o v e r c o m e t w o o f t h e m a i n p r o b l e m s f o r e s e e a b l e , i . e . t h e p l a s m a e m i s s i o nb a c k g r o u n d a n d t h e s c a r c e e x p e c t e d c o n c e n t r a t i o n o f d u s t ( 4 ) .( 1 ) S h a r p e J . P . F u s . E n g . a n d D e s . 6 3 c 4 , 1 5 3 ( 2 0 0 2 ) .( 2 ) C a r m a c k W . J . F u s . E n g . a n d D e s . 5 1 c 5 2 , 4 7 7 ( 2 0 0 0 ) .( 3 ) B a d e r A . e t a l . , R e v . S c i . I n s t r u m . 7 5 , 3 7 0 ( 2 0 0 4 ) .( 4 ) K r a s h e n i n n i k o v S . I . e t a l . , P h y s . P l a s . 1 1 , 3 1 4 1 ( 2 0 0 4 ) .


A n i n v e s t i g a t i o n o f t h e r e l a t i o n s h i p b e t w e e n t o r o i d a l r o t a t i o n a n db o o t s t r a p c u r r e n t i n t h e T J I I s t e l l a r a t o rD . R a p i s a r d a , B . Z u r r o , A . B a c i e r o , V . T r i b a l d o s , E . A s c a s i b a r a n d T J 0 I I t e a mL a b o r a t o r i o N a c i o n a l d e F u s i ó n . E U R A T O M M C I E M A T , 2 8 0 4 0 M a d r i d , S p a i nA b s t r a c t .T h e a c q u i s i t i o n o f t o r o i d a l r o t a t i o n p r o f i l e s i n t h e T J 0 I I s t e l l a r a t o r , b y m e a n s o f t h em e a s u r e m e n t a n d s t u d y o f t h e l i n e s h i f t s o f i o n s l y i n g a t d i f f e r e n t p l a s m a r a d i i , a n d t h e i ri n t e r p r e t a t i o n a r e a d d r e s s e d i n t h i s w o r k . T h e e x p e r i m e n t a l s y s t e m a n d t h e a b s o l u t ec a l i b r a t i o n m e t h o d e m p l o y e d h e r e t o d e t e r m i n e f l o w v e l o c i t i e s a v e r a g e d a l o n g l i n e s 0 o f 0s i g h t h a v e b e e n d e s c r i b e d p r e v i o u s l y ( 1 ) . T y p i c a l l y , d a t a f r o m E C R H d i s c h a r g e s s h o wf l o w v e l o c i t i e s , d e p e n d i n g o n t h e i o n t y p e , t h a t r a n g e b e t w e e n 5 a n d 4 0 k m / s a c r o s s t h ep l a s m a . R e s u l t s o b t a i n e d f o r t o r o i d a l v e l o c i t y p r o f i l e s s u g g e s t t h a t t h e s h a p e o f t h e s ep r o f i l e s m i g h t b e r e l a t e d t o , o r i n f l u e n c e d b y , t h e l o c a l c u r r e n t d e n s i t y , a n d t h e o r d e r s o fm a g n i t u d e o b s e r v e d s u g g e s t a c o m p a r i s o n w i t h b o o t s t r a p c u r r e n t n e o c l a s s i c a l t h e o r y .F u r t h e r m o r e , a c o n s i d e r a t i o n o f t h e n e o c l a s s i c a l i o n i c c o n t r i b u t i o n t o t h i s c u r r e n t i s n o ts u f f i c i e n t t o e x p l a i n t h e l a r g e D o p p l e r s h i f t s o b s e r v e d e x p e r i m e n t a l l y , t h e s e b e i n g a b o u ta f a c t o r 6 g r e a t e r t h a n t h e n e o c l a s s i c a l c o n t r i b u t i o n . N o w , i n o r d e r t o i n v e s t i g a t e i t se f f e c t w e h a v e d e v e l o p e d a m o d e l w h i c h e s t i m a t e s t h e c o n t r i b u t i o n s o f b o t h t h e r a d i a le l e c t r i c f i e l d a n d c u r r e n t s t o t o r o i d a l f l o w . S t a r t i n g f r o m a p l a s m a l o c a l m o d e l w e c a nc a l c u l a t e t h e t e r m s c o n t r i b u t i n g t o t h e t o t a l f l o w ( i . e . , E x B , j ) a n d s i m u l a t e c h o r d 0a v e r a g e d v e l o c i t i e s i n o r d e r t o e s t i m a t e t h e t o t a l p l a s m a c u r r e n t . A c o m p a r i s o n w i t h d a t ao b t a i n e d f r o m t h e T J 0 I I R o g o w s k i c o i l s i s u s e d t o d e m o n s t r a t e t h e v a l i d i t y a n d l i m i t a t i o no f t h i s m o d e l . F i n a l l y , i n o r d e r t o r u l e o u t u n c e r t a i n t i e s a s s o c i a t e d w i t h t h e u s e o fd i f f e r e n t i o n s , t o r o i d a l v e l o c i t y p r o f i l e s f o r a s i n g l e i o n s p e c i e s c o v e r i n g a s i g n i f i c a n tp a r t o f t h e p l a s m a c r o s s 0 s e c t i o n a r e o b t a i n e d u s i n g t h e s h o t 0 t o 0 s h o t t e c h n i q u e .( 1 ) D . R a p i s a r d a e t a l . , P r o c . 3 1 s t E u r o p . P h y s i c s S o c i e t y C o n f . o n C o n t r o l l e d F u s i o n a n dP l a s m a P h y s i c s V o l . 2 8 G , P 0 4 . 1 7 3 ( 2 0 0 4 ) .


Study of Doppler reflectometry viability in TJ-II stellarator using a 2-

dimensional full-wave code

E. Blanco1, T. Estrada1, S. Heuraux2 and J. Sánchez1

1Laboratorio Nacional de Fusión. Asociación Euratom-CIEMAT, 28040 Madrid, Spain

2LPMIA UMR 7040, UHP Nancy I, BP 239, 54506 Vandoeuvre Cedex, France

A two-dimensional full-wave numerical code in the extraordinary mode of propagation has

been developed [1] to simulate reflectometry in TJ-II. The code uses the Finite-Difference

Time-Domain technique to solve the wave propagation in a magnetized and turbulent

plasma. Free propagation through the computational boundaries is achieved by a Perfectly-

Matched-Layer surrounding the computational domain. In order to guarantee the stability of

the code, the current equations are solved using a fourth-order Runge-Kutta method.

Realistic plasma shape and magnetic field distribution are introduced in the code using the

theoretical magnetic surfaces of TJ-II, while density profile and turbulence characteristics

are extrapolated from those obtained experimentally. The probing frequencies involved lie

within the frequency range: 33-50 GHz.

The code has been used to study the viability of the Doppler reflectometry technique in TJ-

II. An important parameter to be decided for optimization of the diagnostic is the antennas

tilt angle. A very small tilt angle would mix the diffraction orders at the receiver, making the

Doppler measurement difficult. On the other hand if the tilt angle is too large it would

require turbulence with very high wave-numbers that in general have low intensity. The code

considers two independent horns, similar to those used in the reflectometer installed in TJ-II

[2]. These horns can be tilted without modifying significantly the radiation pattern. In the

simulations we consider different tilt angles, up to 30 degrees, and we assume that the

plasma rotates at a constant velocity of 3 km/s in the perpendicular direction. The numerical

results obtained modifying the plasma geometry allow us to conclude that the shape of TJ-II

plasmas (cut-off layers with high curvature) makes difficult the optimization of the Doppler

reflectometer. The high curvature limits the spectral resolution and consequently special care

should be taken in optimizing the antennas system.

[1] E. Blanco, S. Heuraux, T. Estrada, J. Sánchez and L. Cupido. Rev. Sci. Intrum 75 (2004) 3822

[2] T. Estrada, E. Blanco, L. Cupido, M.E. Manso and J. Sánchez. This conference.


Influence of the stray light upon TJ-II Thomson scattering profiles

measured in different magnetic configurations

J. Herranz, I. Pastor, and D. López-Bruna

Laboratorio Nacional de Fusión, CIEMAT, Madrid, Spain

In Thomson scattering diagnostics, one must have a very intense laser radiation

source in order to provide an acceptable signal level. Along its trajectory across the

plasma, the input laser beam passes through vacuum windows at its entrance and exit of

the vacuum vessel. At these surfaces, scattering of the laser beam occurs and despite all

kinds of precautions, like light baffles, viewing dumps, high rejection spectral notch

filters or removing the windows far away from the collection area, the intensity of the

stray light can be comparable, or even surpass the whole plasma scattering signal.

In the TJ-II stellarator the intense ruby laser beam intersects the plasma next to

the hard-core surface, where it is not possible to install a proper viewing dump as a

black background. Therefore, multiple scattering of the strong parasitic light from

vacuum surfaces, entrance and exit windows, finally enters into the collection angle of

the spectrometer altering randomly some of the central spectral channels of the spectra.

The influence of this particular noise in the recorded electronic distribution

function is being analysed. This will let us determine and correct the level of distortion

introduced in the electron temperature and density profiles measured by the TS system.

Different deformations brought on the electronic profiles by this unwanted signal will

be evaluated as a function of the varied TJ-II magnetic configurations and constrained

conditions of measurements. In certain magnetic configurations and plasma conditions

(ne !0.5x1019

m-3 and Te !1 keV) the stray light signal can increase the density values

up to 30%, whereas the measured temperatures might drop !15%.

Finally, we will point out the solutions that could be applied both, in the specific

geometry of TJ-II as well as in other conditions where the plasma device is physically

so restrictive.


A code to simulate neutral beams across TJ-II for the exploitation of a

charge-exchange recombination spectroscopy diagnostic

J. M. Carmona, K. J. McCarthy, R. Balbín, J.M Fontdecaba, J. Guasp, I. Pastor, J. Herranz

Laboratorio Nacional de Fusión, Asociación EURATOM-CIEMAT, E-28040 Madrid, Spain

A diagnostic neutral beam injector (DNBI) as well as charge-exchange recombination

spectroscopy (CXRS) and Compact Neutral Particle Analyser diagnostics are being

commissioned for the TJ-II stellarator [1,2]. The DNBI provides neutral beam energies and

equivalent currents up to E = 30 keV and 3.3 equ. A, respectively while the CXRS system is

designed to obtain localised Doppler temperatures and velocities, plus ion density profiles,

with high spatial resolution (!2 cm) from five viewports. Moreover, a flexible coupling to the

TJ-II allows the DNBI to follow the plasma centre when changing magnetic configuration

(i.e., plasma size, centre, radius all vary).

In parallel, a code has been written to model the beam path, its attenuation, charge-

exchange processes and the spectral line emissivity across TJ-II plasmas. This code provides a

visualisation of its path through any magnetic configuration, as well as allowing one to

establish density limits, to optimise viewport usage and to aid data interpretation. The model

takes beam parameters such as focal length, divergence, etc., to determine its composition and

radial distribution, before considering interactions between its three energy components (E,

E/2, E/3) and plasma electrons, protons, neutrals plus impurities to estimate the attenuation

across plasmas. For this, it uses Ne and Te profiles from the Thomson Scattering diagnostic or

from the TJ-II Numerical Library (this also furnishes geometrical coordinates for beam path

visualisation through TJ-II) [3]. The code is being extended to include the effect of beam halo

as well as to obtain totally stripped impurity ions profiles, e.g. C+6, from absolutely calibrated

spectral line profiles, e.g., C VI at 529 nm.

In this paper, after briefly outlining the DNBI and CXRS systems, a detailed

description of the model is given. Next, estimates of beam attenuation performed for different

densities, heating modes, and configurations are given together with illustrations of the beam

traversing magnetic configurations. Also, a description of the modelling of the CXRS

emission and light collection is presented. These results will permit fine-tuning of the model

required for the second stage when experimental impurity emission profiles are to be input.

[1] K.J. McCarthy et al., Rev. Sci. Instrum. 75 (2004) 3499.

[2] R. Balbín et al., to be presented at this conference.

[3] V. Tribaldos et al., Report No. 963, CIEMAT, Madrid 2001.


[1] Vapnik, V., “Statistical Learning Theory”, John Wiley & Sons, INC, 1998.

Application of intelligent classification techniques to the TJ-II

Thomson Scattering diagnostic

J. Vega, I. Pastor, J. L. Cereceda, A. Pereira, J. Herranz, D. Pérez, M. C. Rodríguez

Asociación EURATOM/CIEMAT para Fusión, Madrid, Spain

G. Farias, S. Dormido-Canto, J. Sánchez, R. Dormido, N. Duro, S. Dormido

Dpto. Informática y Automática - UNED, Madrid, Spain

G. Pajares, M. Santos, J. M. de la Cruz

Dpto. Arquitectura de Computadores y Automática - UCM, Madrid, Spain

Intelligent classification techniques can help to automate data analyses processes

in a fusion environment. The laser shot of the TJ-II Thomson diagnostic has been

synchronized with external events and also, an automated image classification system

has been developed. During daily TJ-II operation, Thomson Scattering images can be

essentially of five different types. These classes correspond respectively to CCD camera

background, measurement of stray light without plasma or in a collapsed discharge,

image during ECH phase, image during NBI phase and image after reaching the cut off

density during ECH heating.

After a laser shot, the classifier identifies the kind of image that has been

produced and, according to it, the corresponding analysis processes are executed.

There are two big stages to implement in a signal classification process: features

extraction and signal sorting. In the TJ-II Thomson Scattering case, the first one consists

of performing signal processing trying to extract specific differentiating features of the

image. The main objective has been to obtain a classifier based on a very much reduced

number of features making use of our system knowledge. However, the second phase

makes the image classification from the features extracted in the first stage. Each TJ-II

Thomson Scattering image has 221760 pixels, i.e. 221760 possible features. We have

reduced the dimensionality of the problem to only 9 characteristics (0,004% of the

initial number). The classification stage has been based on “Support Vector Machines”

[1] mainly due to the efficiency of computation during both, system training and image

evaluation. Success rate with the classifier is 95%.

Application of this technique to the stray light identification/evaluation in

images during ECH or NBI phases is being considered.


Relevant improvements in the two color interferometer diagnostic in TJ-II

Stellarator.

M. Sánchez, J. Sánchez

Laboratorio Nacional de Fusión, Asociación EURATOM-CIEMAT, E-28040 Madrid, Spain

A double wavelength heterodyne interferometer (CO2 10.6µm, He-Ne 0.63 µm) diagnostic

has been installed at the TJ-II Stellarator. Even though the main task for this diagnostic is the

measurement of the line average density during NBI discharges (ne >5e19m-3 ), it is also

routinely used during low density (ne ~5e18m-3 ) ECRH operation. In this scenario the system

serves as a backup diagnostic to the microwave interferometer in case of fringe losses, with

the ultimate objective of real time line density measurements.

When this wavelength is used at low densities in a device of moderate dimensions as TJ-II

(a=approx 20cm), very high accuracy in the phase measurement is required.

The CO2 interferometer at TJ-II has been optimised to operate with average noise in the

phase measurement better than 1/400 fringes. This optimisation has been realized by acting

on the gaussian beam parameters and also by using a very flexible digital phase meter

procedure.

The phase meter system, uses a digitizer to record the interferometer four intermediate

frequency (IF) signals (1 MHz) at 8 MHz sampling frequency. The analysis software extracts

the phase evolution and is able to adapt the filters to the spectrum displacements due to

structural vibrations and to subtract cross talk effects. With the high accuracy achieved,

features like the perturbation due heating of the ZnSe vacuum windows by stray ECRH

radiation has been observed. It is corrected by software, using a external signal from a

bolometer probe. As a counterpart, the 8 MHz sampling frequency involves a massive data

storage and calculation time spending in such a way that real time and a future multi-channel

systems would be hindered.

In order to reduce the size of data files and the calculation time, we have applied a under-

sampling technique. Sampling at a rate of 800 KHz and with few modifications in the

algorithm we have obtained the phase and line density without a relevant noise increase and

dynamic characteristics losses. The data size is reduced by 10 and the calculation time by

more than 20. That is in the way of our multi-channel and real time goals.

.


Laser-Based Polarimetry and Interferometry Measurements

in a High-Temperature Plasma

B.H. Deng1, D.L. Brower1, W.X. Ding1, D. Craig2, A.H. Mahdavi

3, V. Mirnov

2, S.C. Prager

2

1University of California at Los Angeles, Los Angeles, California USA2University of Wisconsin-Madison, Madison, Wisconsin USA

3General Atomics, San Diego, CA USA

Both the current density and electron current density are important parameters for

fusion-oriented plasma research. In a high-temperature reversed-field-pinch plasma (RFP), a

high-resolution, vertically-viewing, far-infrared laser system is employed to measure both the

Faraday rotation and electron density simultaneously with time response up to 5

microseconds. A new three-wave laser configuration provides single-shot capability for

constraining magnetic equilibrium reconstructions and determining the current density

distribution. Fast time response combined with low phase noise also enables us to directly

measure magnetic, current density and electron density fluctuations. The temporal dynamics

of these parameters are directly measured throughout the sawtooth cycle. Coherent

interaction between current fluctuations and global magnetic fluctuations are also measured

and observed to generate a non-zero mean electromotive force along the mean magnetic field.

This electromotive force, called the Hall dynamo, significantly redistributes mean current and

also affects ion motion due to a fluctuation-induced torque during magnetic reconnection

events.

A new diagnostic is being developed to measure the well known Fizeau effect whereby

through modest modification of the existing apparatus, the line-integrated poloidal current

density can also be directly measured. This parameter is important since the RFP toroidal

field is determined by currents flowing within the plasma. The Fizeau effect is a phase shift

of an electromagnetic wave associated with movement of a dielectric medium. This motion

can be related directly to the plasma electron current. Determining the Fizeau effect involves

measurement of the phase shift between two collinear, orthogonally-polarized, counter-

propagating laser beams. Estimates indicate that a phase shift of ~2-4 deg. is expected for

typical MST parameters, well within the system resolution. Both the Faraday rotation

polarimeter and Fizeau interferometer diagnostics are directly applicable to ITER.

This work is supported by the U.S. Department of Energy.


Characterization of Ti Kαααα radiation resulting from interaction of ahighly intense laser pulse with a thin titanium foil

J.A. King1,3, M.H. Key1, C.D. Chen1, R.R. Freeman3,7, T. Phillips1, K. Akli1,3, M.Borghesi5, M. Chen1, R.Clarke2, T. Cowan4, S. Hatchett1, R. Heathcote2, J.A. Koch1,K.L.Lancaster2, A.MacKinnon1, P.Norreys2, P.Patel1, L.Romagnani5, R.Snavely1,3, R.

Stephens4, C. Stoeckl6, R. Town1 , M. Zepf 5, B.Zhang3

1Lawrence Livermore National Laboratory, Livermore, CA, USA2Rutherford Appleton Laboratory, Chilton, Oxon, UK

3University of California, Davis, Davis, CA, USA4General Atomics, San Diego, CA, USA

5The Queen’s University of Belfast, Belfast, UK6University of Rochester-LLE, Rochester, NY, USA

7The Ohio State University, Columbus, Ohio 43210, USA

Kα radiation generated by interaction of a highly irradiant (2 x 1016 W/cm2), ultrashort(1ps) laser with thin (25 µm) Ti foils is analyzed using data from a spherical Braggcrystal imager and a single hit CCD spectrometer along with MC simulations of Kαbrightness. Spatially resolved maps of absolute laser intensity and Kα brightness havebeen determined through comparison of relative intensity maps with the total laser energyand total Kα yield. Comparison of total imager counts with Kα yield from the relativelybroadband single hit spectrometer has revealed a reduction in Bragg crystal collectionefficiency for high Kα yield. This reduction of collection efficiency is attributed to anincreased component of ionization state shifted Kα. Laser energy to electron conversionefficiencies have been determined, through comparison of single hit data with MCsimulations, to be 2.8% for the main set and 9.7% for the high yield data. Also, the Kαconversion efficiencies are found to be 1.4x10 -5 for the main set and 4.9x10-5 for the highyield data. Finally, comparison of the number of photons incident upon the crystalaperture with the number of photons incident upon the imaging CCD resulted in aneffective crystal reflectivity of 3.75±2%.

This work was performed under the auspices of the U.S. Department of Energy byUniversity of California Lawrence Livermore National Laboratory under contract No.W-7405-Eng-48.


Observations of the cold pulse propagation during multi-pulse

molecular beam injection on HL-2A

Shi Zhongbing, Ding Xuantong, Yao Lianghua, Liu Zetian, Chen Chengyuan,

Yang Qingwei, Feng Beibin, Zhou Yan, Yan Longwen, Liu Yi, Liu Yong.

Southwestern Institute of Physics, Chengdu 610041, China.

Abstract: Asymmetric cold hydrogen molecule pulse propagation has been observed

by means of electron cyclotron emission (ECE) and soft-X-ray (SXR) array during

multi-pulse molecular beam injection (MBI) experiments on HL-2A. The propagation depth

is about 28cm in low field side and only about 10cm in high field side (see figure 1). The

cold pulses cannot propagate to the plasma center both from low field side and high field side,

and the electron temperature in plasma center is not changed during MBI. Large-scale

electron density pulse perturbations can be observed in the plasma center from the ECE 3rd

harmonic measurements, which is corresponding to the results of the far-infra-red (FIR) laser

interferometer (see figure 2).

Figure 1. Cold pulse propagation

measured by ECE 2nd harmonic during

multi-pulse MBI

Figure 2. Electron density

perturbations in plasma center measured

by FIR laser interferometer and ECE 3rd

harmonic during multi-pulse MBI


Electron Acceleration Near ICRF Antennae

93HWUåtOND1, L. Colas

2, M. Goniche

2, S. Heuraux

3, J.M. Noterdaeme

4,5,

V. Fuchs1, L. Krlín

1

1Association Euratom/IPP.CR, Prague, Czech Republic

2Association Euratom/CEA Cadarache, France

3LPMI, Université Nancy, France

4Association Euratom/IPP Garching, Germany,

5EESA Dep., University Gent, Belgium

It is demonstrated that thermal electrons can be accelerated to energy of several keV,

when moving along magneto-static field lines near the ICRF (Ion Cyclotron Resonance

Frequency) antenna. The electron can gain energy in passing the near antenna rf field

inhomogeneity, because of the temporal phase changes of the field during one quiver

motion period. This process is similar to electron acceleration in front of lower hybrid

wave antennae [1], when the electron passes in front of the septum between wave-guides.

The electron energy rises by repeated passes through the near antenna rf field

inhomogeneity, as the electrons are reflected at the sheath on ICRF antenna components,

like parts of the antenna box and antenna guard limiters, until the electron kinetic energy

reaches or overcomes the sheath potential. In turn, the sheath potential corresponds to the

rectified rf potential and can be enlarged by energetic electrons [4] with the kinetic

energy larger than the sheath potential, which hit the antenna parts. Obviously, the

enlarged sheath potential can cause stronger ion acceleration and plasma convection near

the ICRF antennae [2]. In this way, this acceleration process can participate in creation of

high thermal loads (hot spots) observed on antennae. For the numerical modeling, we use

the rf field as calculated in vacuum by the ICANT code [3]. By using test particle

computations, we estimate the energy gain of electrons as a function of time and as a

function of the RF electric field intensity. An estimate of the growth of the sheath

potential is given, too. In conclusion, a process of electron acceleration near the ICRF

antenna was identified and explored. Supported by the project GACR 202/04/0360.

[1] V. Fuchs et al.,Phys. Plasmas 3 (1996) 4023.

[2] M. Bécoulet et al., Phys. Plasmas 9 (2002) 2619.

[3] S. Pécoul et al., Computer Physics Communications 146 (2002) 166.

[4] D. Tskhakaya, S. Kuhn, V. Petrzilka, R. Khamal, Phys. of Plasmas 9 (2002) 2486.


Fast Particle Energy Measurements in the Scrape-off Layer During Lower

Hybrid Current Drive Experiments on Tore Supra

V. 3HWUåtOND1, M. Goniche2, J. Gunn

2, E. Gauthier

2, J.–Y. Pascal

2, F. äiFHN1

1Assoc. EURATOM-IPP.CR, Za Slovankou 3, 182 21 Praha 8, Czech Republic

2Assoc. EURATOM-CEA-Cadarache, DSM/DRFC, 13108 Saint Paul-lez-Durance, France

A retarding field analyser (RFA) was used during lower hybrid (LH) current drive

experiments in the Tore Supra tokamak to measure the flux of supra-thermal particles

emanating from the near field region in front of the LH grill mouth. The RFA was

reciprocated in ∼250ms up to 1cm behind the last closed flux surface. The RFA entrance slit

was biased to –50 V with respect to the vacuum vessel ground in order to repel thermal

electrons. The ion-repelling grid was grounded such that all ions could reach the collector.

The secondary electron grid was biased to –200 V. For specific values of the safety factor

and of the RFA position, a strong negative current was measured both on the entrance slit

and on the collector. This occurs when at least one of the wave-guide rows is magnetically

connected to the RFA, and only when the launcher is active. The negative current indicates:

(1) the presence of an electron flux that exceeds the ion flux, (2) the applied potentials are

not negative enough to repel the electrons. The negative current is observed at the same

position on the inward and outward parts of the probe reciprocation. The outer edge of the

fast electron layer coincides with the leading edge of the LH antennae within the uncertainty

of the magnetic measurements (at most ±5 mm). The spatial resolution (∼ 5 mm) allows to

assess that the radial width of the collected fast electron beam is less than 1 cm. This result is

consistent with measurements obtained by infra-red imaging of connected in-vessel

components. The electron current on the entrance slit and on the collector comes in rapid

bursts (typical frequency in the 10-20 kHz range). The form of the bursts is very similar on

the collector and on the entrance slit. Qualitative data indicative of the width of the electron

distribution function were obtained. Supported partly by the project GACR 202/04/0360.


High Field Side Penetration Depth Scaling at ASDEX Upgrade

É. Belonohy1, S. Kálvin1, O. Kardaun2, G. Kocsis1, K. Lackner2, P.T. Lang2

and the ASDEX Upgrade Team 1 KFKI Research Institute for Particle and Nuclear Physics, EURATOM Association,

P.O.Box 49, H-1525 Budapest, Hungary 2 MPI für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, D-85748

Garching, Germany

Refueling of fusion plasmas by injection of frozen pellets (hydrogen or deuterium) is

a promising experimental approach in modern tokamak physics. As it has already been

indicated elsewhere, the fueling efficiency can be increased by injecting the pellets from

the high field side (HFS) rather than the conventional low field side (LFS), eg. from the

inner side of the torus, as drift effects accelerate the ablatant radially toward the center

of the plasma.

In order to get a better understanding of pellet ablation physics in tokamak plasmas

and to facilitate future scaling studies for the next generation of tokamaks, a database

for high field side pellet injections was developed using the experimental results

obtained at the international tokamak ASDEX Upgrade. The database contains the most

important experimental parameters of pellet-plasma interaction and extends the already

existing low field side database (IPADBASE).

Based upon this database a statistical multiple regression analysis is performed using

the forward selection method to determine the penetration depth dependence on the

main plasma and pellet parameters, and hence derive a scaling law for pellet ablation. It

is shown, that there exists a dependence on the toroidal magnetic field in addition to

other leading parameters such as the electron temperature and density, pellet mass and

velocity, and the plasma shape.

Finally, a number of theoretical models have been proposed to describe the physics of

pellet ablation in fusion plasmas. The scaling laws for the penetration depth given by

these models are to be compared to the results obtained from the regression analysis of

the experimental data.


Simulation of Pellet Induced Perturbations in Fusion Plasmas for Fueling

and ELM Triggering Scenarios

K. Gál1, A. Kallenbach2, S. Kálvin1,

G. Kocsis1, P. T. Lang2, G. Veres1 and ASDEX Upgrade Team2

1KFKI–Research Institute for Particle and Nuclear Physics,EURATOM Association, P.O.Box

49, H–1525 Budapest–114, HUNGARY2Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2, 85748

Garching, GERMANY

It is well known that beside plasma refueling by pellets, these small ice pieces can as well

be used for ELM triggering [1]. Rising the ELM frequency by external pacemaking results in

a reduced ELM energy, which is essential for the target lifetime in ITER and a future fusion

reactor. Neither the exact mechanism of the ELM release by the pellet nor the reduction of

the ELM energy with rising frequency are yet fully understood. This contribution presents

experimental analyses and simulations of pellet ELM triggering experiments aiming the better

understanding of these phenomena.

The simulation is done using a hybrid model which describes the formation of the neutral

cloud according to the NGS ablation model and the dynamics ofthe ionized cloud part treated

by a one-dimensional Lagrangian cell code. The database containing the main characteristics

of the pellets injected from the HFS in ASDEX Upgrade (presented at this conference [2]) is

used to validate the results of the calculations. The minimum pellet size to trigger ELMs for

single pellet injection as found in ASDEX Upgrade has been verified by our simulations.

The pellet size and velocity for ELM pacemaking in ITER has been estimated by A. R.

Polevoi et al. [3]. We have performed a detailed analysis of the ablation of these estimated pellet

parameters in an ITER like plasma. The ability for ELM triggering and the fueling efficiency

has been determined. In addition the role of the high beta plasmoid which forms as a result of

the pellet ablation is estimated for the expected plasma parameters in ITER.

References

[1] P. T. Lang, Nucl. Fusion44, 665 (2004).

[2] E. Belohony et al, this conference.

[3] A. R. Polevoi, Nucl. Fusion43, 1072 (2003).


Experimental dependence of plasma breakdown on wave polarization in the

TJ-II stellarator

A. Cappa1, F. Castejón1, K. Nagasaki2, F. Tabarés1, A. Fernández1, E. de la Cal1, T. Estrada1

1Laboratorio Nacional de Fusión, Madrid, Spain2Institute of Advanced Energy, University of Kyoto. Japan

Recently, second harmonic ECRH plasma breakdown and its dependence on the initial

conditions such as neutral gas pressure, injected power or beam polarization has been the

subject of theoretical as well as experimental work [1, 2, 3]. Although those studies have been

carried out in the context of stellarators, they are particularly relevant in the case of large

tokamaks, such as ITER, where conventional inductive breakdown is expected to be strongly

improved if ECRH is used.

A matter of interest is the dependence of breakdown time on wave polarization, since it

provides valuable information to understand the processes that take part in plasma breakdown

and, in particular, how important is the effect of the linear wave-particle interactions

compared to the non-linear ones, which are essential to understand second harmonic

breakdown. In the existing theoretical models, wave polarization is not taken into account

because it is assumed that the injected ECRH power is initially scrambled by the vessel walls

and that the discharge growth rate is only due to the non-linear wave-particle interaction

between deeply trapped electrons and the randomized electric field. However, while this

seems reasonable for the very beginning of the discharge, it may not be so as we progress

towards breakdown (marked usually by the first Ha peak ). Actually, as experiments in

Heliotron J have demonstrated, wave polarization must be taken into account and the linear

absorption processes, not considered in the existing models, are probably relevant. In fact,

theoretical modelling in TJ-II had already pointed out the need to include linear interactions in

order to achieve a complete simulation of the breakdown process [4].

The experimental results of the TJ-II plasma breakdown dependence on wave polarization are

presented in this contribution. Its consequences in relation with our understanding of the

second harmonic ECRH breakdown are discussed.

References

[1] A. Cappa, F. Castejón, F.L. Tabarés, D. Tafalla, Nucl. Fusion 41, 363 (2001).[2] K. Nagasaki et al., Nucl. Fusion 45, 13 (2005).[3] J.W. Radder et al., 13th International Stellarator Workshop, Canberra (2002).[4] A. Cappa and F. Castejón, Nucl. Fusion 44, 406 (2004).


Neutral Beam Injection and Fast Ion Confinement in the

MST Reversed Field Pinch

G. Fiksel1, A.D. Beklemishev2, D. Craig1, V.I. Davydenko2, D. Den Hartog1, B. Hudson1,

A.A. Ivanov2, R.Macgee1, R. O'Connel1, S.C. Prager1, J.C. Sarff1, Yu.A. Tsidulko2

1Department of Physics, University of Wisconsin - Madison, Madison, WI, USA

2Budker Institute of Nuclear Physics, Novosibirsk, Russia

A study of confinement of fast ions in the Reversed Field Pinch has been undertaken to

evaluate the efficiency of auxiliary plasma heating as well as the momentum and current drive

via neutral beam injection. While the confinement of the bulk plasma in the RFP

configurations is affected by the magnetic fluctuations and the stochasticity of the magnetic

field, the effect of the stochasticity on the fast ion confinement was unknown.

The experimental studies of fast ion confinement have been conducted through

injection of a high power, short pulse beam of neutral atoms with a maximum energy of 25

keV, a time duration of 1.5 ms, and a total equivalent current up to 35 A for hydrogen atoms

and 30 A for deuterium atoms. The injector has been manufactured by the Budker Institute of

Nuclear Physics, Novosibirsk, Russia.

A short burst of fast neutral injection creates a population of fast ions inside the

plasma with a density up to 0.3% of the plasma density. The confinement of the fast ions was

deduced from the subsequent decay of their concentration following the injection. The

concentration of the fast ions was detected by two diagnostics: a neutral particle analyzer for

measurement of fast charge exchange neutrals resulting from collisions of the fast ions with

the background neutrals, and a neutron detector for measurement of D-D fusion neutrons

resulting from collisions of fast deuterium ions with the bulk deuterium plasma ions.

The results indicate that the fast ion confinement is better than could be expected from

a simple picture of the ions streaming along the stochastic magnetic field. In addition, a

further improvement in the confinement is observed in plasma with lower magnetic

fluctuations. We compare the experimental results with numerical analysis of fast ion

behavior in a stochastic magnetic field.

The work has been supported by the US Department of Energy.


Simulation of Fast Alfvén Wave Interactions with Neutral-Beamand Minority Ions in Tokamaks

V.S. Chan1, M. Choi1, and S.C. Chiu2

1General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA2Sunrise R&M, Solana Beach, California, USA

The Monte-Carlo rf simulation code ORBIT-RF coupled with TORIC full wave solutionsusing a single dominant toroidal and poloidal wave number has demonstrated the consistencyof simulations with previous DIII-D fast wave (FW) experimental results for interactionbetween injected neutral-beam ions and FW, including the measured neutron enhancementand enhanced high energy tail. Comparison with C-Mod fundamental heating discharges alsoyielded reasonable agreement. Predicted power absorption from ORBIT-RF falls within arange of TORIC calculations, which assumed high temperature Maxwellian distributions tomodel the beam ions. This suggests that ORBIT-RF may be used to quantitatively model thenon-Maxwellian ion distribution produced during FW heating. Such information is useful forstudying the role of fast ions on stability and transport in tokamaks. ORBIT-RF solves theHamiltonian guiding center drift equations to follow trajectories of test ions in 2-Daxisymmetric numerical magnetic equilibrium under Coulomb collisions and ICRF quasi-linear heating. Monte-Carlo operators for pitch-angle scattering and drag calculate thechanges of test ions in velocity and pitch angle due to Coulomb collisions between test ionsand background plasma. A rf-induced random walk model describing the fast ion stochasticinteraction with the FW reproduces quasi-linear diffusion in velocity space. 2-D profiles ofFW fields and its wave numbers from TORIC are passed on to ORBIT-RF to calculateperpendicular rf kicks of resonant ions with a generalized arbitrary harmonic. Furtherimprovements to the rf quasilinear operator will be reported.

*Work supported by the U.S. Department of Energy under Grant DE-FG03-95ER54309.


Pellet Injection From Different Locations on DIII-D andExtrapolation to ITER*

L.R. Baylor1, P.B. Parks2, T.C. Jernigan1, S.K. Combs1, N.H. Brooks2,M.E. Fenstermacher3, W.A. Houlberg1, C.J. Lasnier3, and G.L. Schmidt1

1Oak Ridge National Laboratory, Oak Ridge, TN, USA2General Atomics, San Diego, CA, USA

3Lawrence Livermore National Laboratory, Livermore, CA, USA

Deuterium pellet injection has been used in experiments on the DIII-D tokamak toinvestigate fueling in reactor relevant plasma regimes. The versatile pellet injection systemallows injection from two ports on the inner wall, two vertical ports and an outside midplaneport. The fueling efficiency and mass deposition profiles have been measured from pelletsinjected from all locations. The inner wall injection locations lead to deeper mass penetrationand significantly higher fueling efficiency than the others. A major radius displacement of thedeposited pellet mass is observed from all injection locations and is hypothesized to occurfrom ∇B and curvature induced drift effects. Differences in the edge localized mode (ELM)characteristics triggered from pellets injected into H-mode plasmas from the different pelletinjection locations have been measured and are described. Most notably the radiated powerdeposited in the divertor is significantly lower from ELMs triggered by the inner wall pelletsthan from the inherent background ELMs.

The mass deposition from pellets injected into DIII-D plasmas has been modeled usingthe Pressure Relaxation Lagrangian (PRL) model [1] coupled to the PELLET ablation code[2]. New features added to the PRL model include curvature drive from parallel flows andmagnetic shear induced mass shedding. With these new effects included, the modeleddeposition profiles are in reasonable agreement with experiment from all the injectionlocations. ITER will require efficient pellet fueling to operate at the proposed high densityand is designed to have inner wall injection capability. The proposed pellet fueling scenariofor ITER has been modeled using the PRL model and the resulting mass deposition for the3 mm and 5 mm pellets looks very encouraging for reaching deep into the plasma. Scaling ofthe mass deposition on DIII-D with key plasma parameters is under study and will bepresented along with comparison of the scaling with the PRL model.[1] P.B. Parks and L.R. Baylor, to be published in Phys. Rev. Lett.[2] W.A. Houlberg, S.L. Milora, and S.E. Attenberger, Nucl. Fusion 28, 595 (1988).∗Work supported by U.S. Department of Energy under DE-AC05-00OR22725, DE-FC02-04ER54798, and W-7405-ENG-48.


Observation and Modeling of Ion Cyclotron Range of Frequencies

Waves in the Mode Conversion Region of Alcator C-Mod

Y. Lin1, S. Wukitch1, A. Parisot1, J. C. Wright1, N. Basse1, P. Bonoli1,

E. Edlund1, L. Lin1, M. Porkolab1 G. Schilling2, P. Phillips3

1 Plasma Science and Fusion Center, M.I.T., Cambridge, MA 02139, USA2 Plasma Physics Laboratory, Princeton, NJ 08543, USA

3 Fusion Research Center, University of Texas, Austin, TX 78712, USA

Mode conversion process at the ion cyclotron range of frequencies (ICRF) can be used

to directly heat electrons, drive plasma current and perhaps plasma flow in tokamaks. In

previous studies, the mode converted ion cyclotron wave (MC ICW) was observed in the

Alcator C-Mod tokamak [1, 2]. Recently, the fast magnetosonic wave (FW), MC ICW and

ion Bernstein wave (MC IBW) have all been observed and unambiguously identified in

the mode conversion region of Alcator C-Mod. The influences of the species mix, mode

conversion location andBpol/Btot have been studied in D(3He) plasmas at B0 ∼ 5.4 T

( fRF = 50 MHz) and B0 ∼ 8 T ( fRF = 78 MHz). The RF waves were measured by a

phase contrast imaging (PCI) system using a heterodyne scheme [1]. A synthetic PCI

diagnostic is developed based upon an improved parallel version of the two-dimensional

full wave code TORIC [3]. The experimental observation is compared with the result

from the synthetic PCI diagnostic [4, 5]. Good agreement between the observation and

modeling has been obtained on the spatial structure of the RF waves. When the mode

conversion layer was off axis, both MC ICW and MC IBW were observed. In 5.4 T

near axis mode conversion discharges, double hump spatial structure of the MC waves

was observed experimentally and reproduced by the synthetic PCI. Such structure is an

indication of the up-down asymmetry of the MC ICW. By moving the mode conversion

layer near the axis, in discharges at 8 T, we had the first definitive observation of IBW

dominated MC in Alcator C-Mod.

References[1] E. Nelson-Melby, M. Porkolabet al, Phys. Rev. Letts.90, 155004 (2003).[2] Y. Lin, S. J. Wukitchet al, Phys. Plasmas,11, 2466 (2004).[3] J. C. Wright, P. T. Bonoli, M. Brambillaet al, Phys. Plasmas,11, 2473 (2004).[4] S. Wukitch, Y. Lin, A. Parisot, J. C. Wrightet al, Phys. Plasmas, accepted for publi-

cation.[5] M. Porkolabet al, Proc. 20th IAEA Fusion Energy Conference, EX/P4-32 (2004).


Auxiliary Heating and Current Drive Systems for the Madison Symmetric

Torus Reversed Field Pinch

J.A. Goetz, J.K. Anderson, A.P. Blair, M. Cengher, G. Fiksel, C.B. Forest, B. Hudson, M.C.

Kaufman, K.J. McCollam, S.C. Prager, J.S. Sarff, M.A. Thomas, and the MST Team

Department of Physics, University of Wisconsin, Madison, WI 53706, USA

Control of the current density profile in MST has led to reduced magnetic fluctuations

and transport, and much improved confinement. In addition, external heating of the plasma

will allow for exploration of the beta limit in the RFP and its effects on transport and

confinement. Techniques to apply controlled auxiliary power to the MST plasma and explore

these physics issues are now being developed. These methods include pulsed parallel current

drive (PPCD), oscillating field current drive (OFCD), neutral beam injection (NBI), lower

hybrid waves (LH), and electron Bernstein waves (EB).

Both LH and EB wave injection are being developed to explore the physics issues of

current drive in the RFP. Antenna design for both techniques poses significant challenges in

the MST environment. A traveling wave LH antenna has demonstrated a power handling

capability of 80 kW with a good impedance match to the plasma over a wide range of

conditions in standard plasmas. Hard x-ray emission has been observed when sufficient

power flows through the antenna. For EB wave injection, a rotatable twin waveguide

antenna that launches electromagnetic waves at power levels up to 150 kW has been

developed. Studies performed at low power (<10 W) have identified the optimal launch

angle for coupling to the EB wave near the plasma boundary.

PPCD is an inductive current drive method and has been used to improve plasma

performance. A system to correct field errors has recently been installed on MST, thus

allowing for operation at higher plasma currents. The addition of variable inductors to the

PPCD circuit will allow for optimization of the method at these higher currents. OFCD is a

helicity injection method being tested as a way to drive net current or to alter the current

density profile. A moderate power system (~250 kW) applies poloidal and toroidal loop

voltages inductively at 250 – 500 Hz. To date, OFCD has demonstrated current drive of 10%

of the toroidal plasma current. Feasibility tests of NBI as an effective way to heat RFP

plasmas are underway. A nominal 1 MW - 1 ms neutral beam, either hydrogen or deuterium,

is being used on MST. Initial studies indicate that fast ion confinement may not be degraded

by the stochasticity of the RFP magnetic field [see G. Fiksel, et al., this conference].


Poloidal H-alpha monitor and visible TV system design for long diagnostic port of KSTAR

H. K. Na, D. C. Seo

National Fusion R&D center, Korea Basic Science Institute, Daejeon, 305-333, Korea

KSTAR has long diagnostic port between vacuum vessel and cryostat so re-entrant cassette is developed

in order that diagnostic system easily access to plasma. Front side of cassette consists of several windows

with circular shape to see plasma. Many diagnostic systems are installed inner side of re-entrant cassette.

Especially poloidal H-alpha monitor located on upper window of Bay J re-entrant cassette is developed to

observe neutral density distribution of inner divertor region of KSTAR plasma. It consists of 10 optical

fiber channels and collection optics with several optical stages. Quarts fiber array locates along the focal

plane of collection lens. H-alpha signal from plasma is delivered to silicon detector through 80m long

optical fiber. Also optical band pass filter with 1/2 inch diameter locates just front of the detector. Spatial

resolution of each line of sight is estimated about 20mm. Visible TV system is developed to monitor

plasma fluctuation and inspect plasma facing component of inner wall of vacuum vessel. TV system

consists of fiber bundle and fiberscope with objective lens. The length of fiber bundle is 6m long and

front end of fiberscope system can be easily bent with various angle to monitor target area. The field of

view of objective lens is almost 45 degree covering divertor and mid plane region of plasma. Also

objective lens is convertible with others to get different viewing angle using optical adapter. Time

resolution of TV system is 48 fps with 1024x1024 pixel format and it will be upgraded with high speed

camera later.


Safety analysis of abnormal fueling in ITER using SAFALY

J. Dies, J. Izquierdo, J. Garcia, C.Tapia, G. Cortes

FEEL - Fusion Energy Engineering Laboratory

Escola Tècnica Superior d'Enginyeria Industrial de Barcelona

Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya

Barcelona, Spain

SAFALY is a hybrid code comprising a zero dimensional plasma dynamics and a quasi two

dimensional thermal analysis of in-vessel components. It was initially adopted to assess

abnormal events in fusion reactors from the safety point of view [01] and was progressively

improved to discuss burn control, confinement mode transition or impurities transport

among others in ITER EDA. Now, the Departament de Física i Enginyeria Nuclear of the

Universitat Politècnica de Catalunya have made suitable SAFALY for ITER FEAT in

order to simulate several accident scenarios [02] challenging the integrity of the vacuum

vessel and the other in-vessel components.

The first scenarios to be simulated have been those related to fueling abnormalities, such as

overfueling by a factor 1.5, overfueling by a factor 3 and sudden suspension of fueling.

Results for ITER FEAT at 400MW steady state mode show a coherent agreement with

previous studies although some parameters and models have to be comprehensively

reviewed yet. In these scenarios plasma is terminated due to disruptions without damage of

in-vessel components and design structure temperatures don’t go beyond the design values.

These events, analysed in the past for ITER EDA [01], have been selected as a first check

of the modifications introduced in the original SAFALY.

__________________

[01] T. Honda, H.W. Bartels, N.A. Uckan, Y. Seki, T. Okazaki, “Development of Safety

Assessment Method for Plasma Anomaly Events in Fusion Reactors”. Journal of Nuclear

Science and Technology,. Vol. 34(3), pp. 229-239, March 1997

[02] J. Izquierdo, N.P Taylor, J. Dies, J. García, F. Albajar, “Progress in the development of

a PIE-PIT for the ITER Tokamak", 23rd SOFT, pp. 373, Sept. 2004


Source Regulation of Fast Energetic Particle Driven Alfvén Modes

Dynamics

G. Vlad, S. Briguglio, G. Fogaccia, F. Zonca

Associazione Euratom-ENEA sulla Fusione, C.R. Frascati, C.P. 65 - I-00044 - Frascati,

Rome, Italy

In a previous paper [1] and on the basis of particle simulation results we have shown that

saturation of Alfvén modes driven unstable by fusion-produced alpha particles can induce a

broadening of the alpha particle pressure profile in some of the proposed ITER scenarios (e.g.,

the reversed-shear SC4 scenario). The validity limit of these results is mainly due to the absence

of fast ion sources in our particle simulations and to the fact that they do not address the particle

nonlinear dynamics on transport time scale. The stability of a given scenario is then analyzed

by assuming the reference equilibrium, i.e. without considering how its formation is affected

by the Alfvén mode dynamics itself. A proper multiple time-scale approach should describe the

evolution of a succession of quasi-equilibria characterized by increasing values of the alpha-

particle pressure gradient. The fast Alfvén mode dynamics affecting each quasi-equilibrium

could distort the alpha-particle distribution function in such a way to modify the next quasi-

equilibrium dynamics. The final scenario configuration, reached in this way, could then differ

from that obtained in Ref. [1], possibly with milder effects on the alpha-particle redistribution

and transport. In this paper we address this point, by simulating the building up of the alpha-

particle pressure profile (though on time scales much shorter than the real one) by amodel

alpha-particle source term. We compare the results obtained in a simulation without source

terms, characterized by quite significant broadening of the alpha-particle pressure profile, with

those obtained by starting with a lower initial alpha-particle pressure gradient and allowing for

the source term to increase the alpha-particle pressure along several different paths. We find

that, in some cases, the latter simulations exhibit a partial regulation of the nonlinear effects,

with a final pressure profile broadening less pronounced than that obtained in the former one.

The dependence of such a regulation on the source dynamics is examined.

References

[1] Vlad G., Briguglio S., Fogaccia G., Zonca F. and Schneider M. 2004, Paper IAEA-CSP-

25/CD/IT/P3-31, presented at the 20th IAEA FEC, Nov. 1-6 2004, Vilamoura, Portugal.

Submitted to Nucl. Fusion


A simulation code for the extraction of H- ions

F. Sattin1, A. Tanga2, M. Cavenago3, V. Antoni1

1 Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy 2 Max-Planck-Institut für PlasmaPhysik, Boltzmannstr. 2, 85748 Garching, Germany

3 INFN-LNL, viale dell'Universita`, I-35020 Legnaro (PD), Italy Negative ion sources have since long been proposed as suitable production means of

fast particle beams to be used in ITER as additional heating mechanisms. The

numerical simulation of the particle production and extraction mechanisms within

these sources is a valuable tool towards their optimisation. A challenging aspect of the

problem of producing a realistic consistent model of the external applied fields,

extracted particles and plasma boundary has been the large difference between the

microscopic characteristic Debye Length and the macroscopic size of the actual

geometry. Therefore most of the work has been focussed on describing the extraction

region over distances of the order of Debye sheath length, leading to such a small

values that any macroscopical description-aimed at describing details over spatial

scales of order of 10-2 m and larger-cannot be performed using realistic computer

resources. A numerical code has been developed ex-novo for this problem. The model

has been reduced to one of electrostatics coupled self-consistently to plasma

dynamics, in which electric fields are both applied from the outside as well as partly

generated by the motion of the charged particles. Non-trivial boundary conditions are

supplemented, due to the complicated geometry of sources. The electrostatic problem

is solved using a given plasma background. A Monte-Carlo module, using the

potential computed in the previous step, produces a map of particle density, which is

fed into Poisson equation for a re-evaluation of potential. The whole process may be

repeated as long as convergence is reached. The code works well in cases where the

plasma density acts as a perturbation over the potential profiles or, equivalently, in the

approximation of very strong applied extracting potentials compared to the plasma

potential. The geometry used includes values of electrical and magnetic fields similar

to those used for the RF Negative Ion Source, under development for the ITER

injector. First results include: 1) an assessment of the relative effectiveness of surface

production versus volume production for extracting negative ions; 2) a study of the

effectiveness of a magnetic filter in confining electrons away from the extraction

region.


Identification of a dynamic model of plasma current density profile

G. De Tommasi1, T. Tala

2, F. Crisanti

3, M. Ariola

1, A. Pironti

1

and contributors to the EFDA-JET workprogramme,

1 Associazione Euratom/ENEA/CREATE – Università “Federico II”, Napoli, ITALY

2 Association EURATOM-Tekes, VTT Processes, P.O. Box 1608, FIN-02044 VTT, FINLAND

3 Associazione Euratom/ENEA, Frascati, ITALY

One of the main mechanisms that enable the ITB formation is the modification of the

current profile using the additional heating and current drive actuators (NBI, LHCD and

ICRH). The ITBs formation and sustainment are strongly linked with the safety factor

and magnetic shear profiles, consequently it is necessary to control both the pressure

and the current profiles, acting on the additional heating systems with a feedback

controller. The design of such a controller relies on the estimation of a model capable to

describe the plasma evolution. This paper introduces a dynamic model with a “grey-

box” structure for the plasma current profile. The model takes the additional heating

powers as inputs, while it gives the plasma current density as output. Several

assumptions on the physics of the process have been done and the full experimental

system has been analyzed in a number of actual blocks that are identified separately (i.e.

a diffusive model for the plasma current, a static model for the link between additional

heating powers and the driven and bootstrap currents profiles). Moreover all the blocks

are assumed to be non-linear, to achieve more flexibility of the model. The overall

model will be the interconnection of all these blocks. The identification has been carried

out using data from JETTO simulations of an actual JET ITB experiment. Such an

approach is quite different from the “black-box” one, where the plasma dynamic

identification is carried out without doing any assumption on the model structure. The

modular approach presented in this paper differs from the one recently used at JET to

design a real-time profiles controller ([1]), where a single “grey-box” linear block has

been used to identify the overall system. In this paper an overview of both the model

structure (with all the used blocks) and of the identification procedure will be given.

Eventually the outputs of the models for the driven and bootstrap current profiles will

be shown. A comparison between JETTO and these blocks will also be given.

[1] L. Laborde, “A multiple-time-scale approach to the control of internal transport barriers on JET”, submitted to 32nd EPS,

Tarragona Spain.

, See Appendix of J. Pamela et al., Fusion Energy 2004 (Proc. 20th Int. Conf. Vilamoura, 2004) IAEA, Vienna (2004)


B2-Eirene (SOLPS) Modelling of JET SOL plasma flow

X. Bonnin1, R.A. Pitts2, D. Coster3 and contributors to the JET-EDFA work programme 1 CNRS-LIMHP, UPR 1311, Université Paris XIII, Villetaneuse, France

2 CRPP, Association EURATOM-Confédération Suisse, EPFL, Lausanne, Switzerland 3 MPI für Plasmaphysik, EURATOM-IPP Association, Garching, Germany

“There’s a hurricane in the edge.” – P. Stangeby

The scrape-off layer (SOL) of tokamak plasmas is home to very strong plasma flows,

which are still relatively poorly understood. Recent Mach probe measurements, at the top of the

poloidal cross-section [1], have confirmed their existence in JET. The radial profile of the

parallel flow Mach number, M||, rises from M|| ~ 0.2 in the separatrix vicinity to a peak of M|| ~

0.5 in the near SOL for forward field operation (i.e. with the ion B× B drift directed

downwards and where positive flow corresponds to the direction from outer to inner divertor

targets). In reversed field, the flow is observed to stagnate throughout the SOL except near the

separatrix, where the flow increases again to the forward field value.

Modelling efforts using the EDGE2D/NIMBUS coupled fluid-Monte-Carlo neutral

code and including drift effects [1] have failed to reproduce the flow magnitude and have only

qualitatively matched the profile shape. We report here on equivalent efforts using the

alternative code package SOLPS5.0 (B2-EIRENE). We obtain M|| values up to 0.4 for the outer

SOL in forward field and an average flow (without drifts) of order M|| ~ 0.05 to 0.10 (about

twice the EDGE2D result, but lower than experiment, M|| ~ 0.2).

This activity complements the ongoing benchmarking exercise between the above two

codes [2,3]. To avoid the added complexity of high recycling near the targets, low density,

attached divertor plasma conditions were selected. Both impurities and classical drifts were

included in the simulation. The same set of experimentally obtained SOL and divertor plasma

profiles was used to constrain both the SOLPS and EGDE2D simulations. The radial transport

coefficients providing the best match to the experiment are compared between the codes, and

related to a range of theoretical predictions.

[1] S.K. Erents, R.A. Pitts, W. Fundamenski et al., PPCF 46 (2004) 1757.

[2] A. Huber, P. Andrew, P. Coad, et al., this conference.

[3] D. Coster, X. Bonnin, G. Corrigan, et al., J. Nucl. Mater. 337-339 (2005) 366.


Guiding-centre simulations of ion orbit loss heat loads

on JET divertor targets

S. Sipilä1, W. Fundamenski

2, and contributors to the EFDA-JET workprogramme

*

1 Euratom-Tekes Assn, Helsinki U. of Technology, P.O.B. 2200, 02015 TKK, Finland

2 Euratom/UKAEA Fusion Assn, Culham Science Centre, Abingdon, OX14 3DB, U.K.

A thorough understanding of the mechanisms affecting heat and particle loading on the

divertor targets is of key importance in designing next-generation tokamaks of reactor-scale

size and power. Ion orbit loss is one important mechanism contributing to the target loads

observed, e.g., in JET, and it is to a large extent responsible for the strong peaking of these

profiles near the magnetic strike point.

The Monte Carlo guiding-centre code ASCOT, using actual JET geometry, has been applied

to studies of a wide range of phenomena affecting the target loads caused by ion orbit loss. A

range of parameter scans were performed in which the radial electric field (Er) inside the

separatrix was calculated self-consistently (e.g., normal vs. reversed magnetic field, scrape-

off layer (SOL) Er magnitude, density and temperature pedestal width and height, ion mass

and charge, etc.). A large number of trace simulations were also performed in order to assess

the load contributions to the inner and outer divertor targets from different initial locations

inside the separatrix. As part of the trace analysis the importance of magnetic field ripple and

anomalous radial diffusion (D⊥,an > 0) was also investigated. The former was found to be

insignificant at JET (with 32 TF coils), while the latter presented a strong equalizing effect on

the inner and outer target loads.

The strong dependence of simulated direct (no collisions in the SOL) ion orbit loss load

profiles on the magnetic field direction, contrary to experiment, indicates that it is not the

dominant energy transport mechanism in the pedestal and near-SOL. This suggests that ion

collisional diffusion in the SOL must be taken into account, which is consistent with previous

indications that (neo-)classical ion conduction plays a leading role in the SOL radial energy

transport. A series of ASCOT simulations constituting a SOL/divertor collisionality scan

clearly show a broadening of target profiles due to ion-ion and ion-neutral collisions. With

normal magnetic field direction, the load on the inner target was found to be much more

sensitive to SOL/divertor collisionality than the load on the outer target.

* See the Appendix of J. Paméla et al., Fusion Energy 2004 (Proc. 20th Int. Conf. Vilamoura, 2004) IAEA,

Vienna (2004).


Modelling JET divertor physics with the EDGE2D Code

A. Huber1, P. Andrew2, P. Coad2, G. Corrigan2, K. Erents2, W. Fundamenski2, S. Jachmich3,A. Korotkov2, G.F. Matthews2, Ph. Mertens1, V. Philipps1, R. Pitts4, J. Rapp1, B. Schweer1,

G. Sergienko1, M. Stamp2 and contributors to the EFDA-JET workprogramme*

1Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Association, TrilateralEuregio Cluster, D-52425 Jülich, Germany

2Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB, UK3Laboratory for Plasmaphysics, ERM/KMS, Association EURATOM-Belgian State, Brussels, Belgium

4CRPP, Association EURATOM-Confederation Suisse, EPFL, Lausanne, Switzerland

L-mode density limit discharges in forward and reversed toroidal field configurations are analysed

with the EDGE2D/NIMBUS code package. EDGE2D solves the fluid equations for conservation of

particles, momentum and energy for hydrogenic and impurity ions (all charge states), while neutrals

are followed with the Monte-Carlo module NIMBUS. The code includes classical drifts (E×B,

curvature, etc.), relevant atomic and molecular physics (ionisation, charge-exchange, recombination,

etc.), impurity radiation from each charge state, and both physical and chemical sputtering of the CFC

divertor target plates.

The experimentally observed outer-inner divertor power asymmetry Ptouter/Pt

inner could not be

explained by the asymmetry in the tomographically resolved divertor radiation alone [1]. The unequal

power sharing between the two targets is most likely caused by the larger outboard area and enhanced

radial transport on the bad curvature, low field side (which are independent of the B∇×B -direction),

and classical drift effects which reverse with the B∇×B -direction. EDGE2D modelling shows that

the former effects alone lead to Ptouter/Pt

inner ~ 2 – 3, which compares well with the observed value of ~

2.2. With B∇×B down, the simulated asymmetry increases up to ~ 5 with the power entering the

SOL, PSOL, while with BB ∇× up, it decreases to ~1.8, in agreement with experimental observation.

This indicates that classical (poloidal) drifts are indeed responsible for the observed variation in

Ptouter/Pt

inner. Similar conclusions were drawn based on the SOLPS5 modelling [2].

In addition, the EDGE2D simulations successfully reproduce the observed asymmetries in divertor

density and electron temperature, and the atomic carbon (CIII) emission profiles; on the other hand,

the Dα emission profile was only well matched under attached conditions. While EDGE2D

successfully reproduces the anticipated parallel pressure drop accompanying divertor detachment, it

strongly underestimates the divertor Dα light, and can not reproduce the gradual plasma flux

reduction (roll-over behaviour) observed under detached conditions.

[1] A. Huber et al., J. Nucl. Mater. (2005) in press.[2] X. Bonnin et al., this conference.

*See the Appendix of J. Pamela et al., Proc. IAEA Fusion Energy Conference 2004 (Vilamoura, 2004)


Transport balance of RF-heated impurity ions

D. Pilipenko1, M. Z Tokar2, B. Weyssow1, I. Pavlenko1 and contributors to the EFDA-JET

Workprogramme∗

1 Universite Libre de Bruxelles, Association EURATOM-Etat Belge, Campus Plain CP231,1050 Brussels, Belgium

2Institut fur Plasmaphysik, Forschungszentrum Julich GmbH, EURATOM Association,D-52425 Julich, Germany

Operation in impurity seeding mode needs a control of seeded impurity behavior to avoid the

accumulation of the impurity ions in the plasma core. One of the possible ways to control

the puffed impurity is to apply the radio-frequency (RF) waves. The purpose of this work is

to study the possibility of using ICRH for impurity density control, including impurity ex-

haust, in impurity seeded fusion discharge. When the absorption of RF power by the selected

impurity ionization state is high enough a difference between temperatures of the main and

impurity ions becomes essential. Up to now the impurity temperature is disregarded in trans-

port modeling and it is normally assumed to be equal to the temperature of the main ions. We

show that to simulate correctly the impurity transport under condition of the strong heating of

a selected impurity ionized state the heat balance equations for the impurity should be solved.

The numerical simulations of the selected impurity heating have been carried out for typical

JET parameters with argon puffed in deuterium plasma. The absorption power profiles were

calculated by full wave code TORIC [1]. A direct loss of impurity ions due to scattering into

first orbit loss cone is calculated using an ion bounce-averaged Fokker-Planck solver with a

nonlinear collisional operator. Finally, ICRF-induced losses [2, 3] are included in the trans-

port code RITM [4]. The three codes are used repeatedly until a self-consistent picture of

the impurity transport in reached. The impact of impurity heating on the heat transport and

intensity of impurity radiation has been shown. Simulated argon density profiles demonstrate

a local reduction of the Ar18+ concentrations during ICRF heating. The results of the quanti-

tative analysis of the transport alteration in the regime of essential ICRF impurity heating are

presented.

[1] Brambilla M. Plasma Physics and Controlled Fusion 41 (1999) 1-34.

[2] Hellsten T. et al, Nuclear Fusion 44 (2004) 892-908.

[3] Chen L. et al, Nuclear Fusion 28 (1988) 389-398.

[4] Tokar M.Z. Plasma Physics and Controlled Fusion 36 (1994) 1819

∗See the Appendix of J.Pamela et al., Fusion Energy 2004 (Proc. 20th Int. Conf. Vilamoura, 2004) IAEA,

Vienna (2004).


Effect of density fluctuations on lower hybrid ray tracing and q-profile

evolution in transport simulations

K.M Rantamäki1, A.N. Saveliev

2, T.J.J. Tala

1, J.A. Heikkinen

1, P.I. Strand

3, J. Weiland

3,

G. Corrigan4 and EFDA-JET contributors*

1Association Euratom-Tekes VTT Processes, P.O.Box 1608, FI-02044 VTT, Finland

2A.F. Ioffe Physico-Technical Institute, St.Petersburg, Russia

3Association Euratom- VR, Chalmers University of Technology, Gothenburg, Sweden

4Association Euratom - UKAEA, Culham Science Centre, Abingdon, OX14 3DB, UK

*See the appendix of J. Pamela et al., Fusion Energy 2004(Proc. 20th Int. Conf. Vilamoura, 2004), IAEA, Vienna

To investigate LH wave propagation in tokamaks, it is important to model scattering of lower

hybrid waves by density fluctuations inside the plasma in addition to standard ray-tracing. In

this work, a simple technique to include the scattering in the FRTC code [1] is considered.

The density fluctuations due to electrostatic turbulence are accounted for by a random

rotation of the wave vector in the plane perpendicular to the magnetic field, so as to keep the

wave number and its parallel component constant. The angle of the rotation is obtained with a

Monte-Carlo operator β = K (2D∆t)1/2

. Its magnitude is obtained from the average fluctuation

amplitude. Here, the coefficient K = ±1 is randomly chosen, ∆t is obtained with the help of

group velocity and the diffusion coefficient D is found as [2,3]

2

0

2

2

32

0

Ω=

⊥⊥ ce

pen

k

k

n

dn

kD

ω

ωω. (1)

Here, ω0 and k⊥ denote the wave angular frequency and perpendicular wave number, Ωce and

ωpe the electron cyclotron and plasma frequencies, dn/n the relative density fluctuation level

(in a statistical sense), and kn is the perpendicular wave number of the fluctuations with the

highest dn/n. Both kn and dn/n are obtained either from a transport model or in the future

from density fluctuation measurements.

Preliminary simulations using the stand-alone FRTC with scattering operator shows that the

density fluctuations have a strong effect on LH driven current density profiles. Assuming

dn/n≈0.3 with a Gaussian density fluctuation level centred at the edge, the main peak in LH

driven current density profile can change from r/a≈0.4 to r/a≈0.6. In future this model is

installed into FRTC inside the JETTO transport code, in order to be able document the effect

of LH wave propagation from density fluctuations on the q-profile evolution in JET.

[1] A.Esterkin and A.Piliya, Nuclear Fusion 36 (1996)1501; A.D. Piliya and A.N. Saveliev,

Report JET-R(98)01, http://www.iop.org/Jet/article?JETR98001&JETR98001

[2] P.L. Andrews and F.W. Perkins, Phys.Fluids 26(1983)2537

[3] F. Santini, “Developments in lower hybrid theory”, Course and Workshop on Applica-

tions of RF Waves to Tokamak Plasmas, Varenna, September 5-14, 1985, Vol I, p. 251.


!!∀

#

∃ ∀ %

&∋(

!∀)

!&∗( ∀

&∋( &∗(∃ ! &∋(

+ ∀ , ∃

−

+,. . ∃/∀,

!! 0.∀

&∋( ∀1∀0 ∃ ∀2∀0∃ ∀∀, 30

4 0 0

. 5 ∗667∋768−∋7∗∋∀

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Radial Electric Field in Toroidal Systems and a Thermoelectric Field of Plasma

V. A. Rantsev-Kartinov

INF RRC "Kurchatov Institute", Moscow, Russia, [email protected]

According to [1], from experimental distributions only key parameters of plasma - Te (!),

Ti (!) and Zeff (!) it is possible to receive spatial distribution of thermoelectric potential/field

(TEF), namely, ϕ r =α(Te(ρ), Ti(ρ), Zeff(ρ)), where ∀ - a functional of above-mentioned pro-

files. The radial TEF, Er = - ∇ϕ r(ρ). The TEF is caused by the taking into account the so-

called dynamical de-screening of the conventional static, Debye screening of the charged

particles in inhomogeneous plasmas (at the account of their motion and mass distinction).

The TEF is formed at microscopic scales, and it is shown at macroscopic scales. The basis

of the TEF is attractive that it is calculated from the first principles [1a, b].

Calculation of the TEF allows to estimate: a) thin structure of an electric field of plasma

and distribution of velocity of its rotation in toroidal systems; b) to compare the calculated

distributions of these velocities with experimentally measured ones, to determine their con-

formity to the equation of balance of forces, and also to define parameters of "tail" of the ra-

dial distribution of plasma particles which can appear as by-product of additional heating.

In the paper it is submitted the results of such calculations on the basis of the published

experimental data of the DIII-D tokamak and Japanese stellarator – the CHS. Results of the

carried out calculations show a good compliance of the received values with the experimen-

tal ones.

REFERENCES

1. V. P. Krainov, V. A. Rantsev-Kartinov, E. E. Trofimovich: a Preprint of the RRC "Kur-

chatov Institute", IAE 5861/6, (1995); b) In Proceeding of International Conference Strongly

Coupled Column Systems-97 edited by Gabor J.Kalman, Krastan B.Blagoev, and J.Martin

Rommel, Plenum Press, New York, (1998), p. 119; c) Ibd, p.124; d) Ibd, p. 119; f) Ibd, p.

114.


mailto:[email protected]

Self-Consistent Simulation of Electron Cyclotron Radiation Transport

and Superthermal Electron Kinetics in Hot Tokamak Plasmas

K.V. Cherepanov, A.B. Kukushkin,

NFI RRC "Kurchatov Institute", Moscow, 123182, Russia

Numerical studies, with help of the code CYNEQ [1(a)], of the contribution of

superthermal electrons to electron cyclotron radiation (ECR) transport in hot plasmas (Te

> 10 keV) confined by a strong toroidal magnetic field (B > 5 T) revealed strong

sensitivity of the net ECR power loss profile, PEC(r), to superthermal electrons. In

particular, for ITER-like conditions (regime “Inductive” [2], Te(0) ~ 25 keV), local rise of

PEC(r), caused by ~10% fraction with locally doubled temperature in the core, makes the

value PEC(0) a noticeable part of the fusion power in the core (cf. [2]). This qualitatively

agrees with ASTRA + CYTRAN code-based analysis [3] which showed significance of

local/global contribution of ECR for purely maxwellian electron velocity distribution

(EVD) in ITER regimes “Steady-State” which need higher temperatures (Te(0) ~ 35 - 45

keV). These results suggested the necessity of a self-consistent treatment of (i) kinetics of

superthermal electrons and (ii) ECR transport. Numerical solution of such a problem

under reasonable assumptions (isotropy of EVD in pitch angles, etc.) by an iterative

procedure (the code CYNEQ-KIN) appeared [1(b)] to be converging very fast.

Here we report in detail on the major physics effect in the self-consistent treatment –

competition of (i) depletion of EVD’s “tail” due to radiation emission, (ii) tail’s

growth/flattening due to radiation absorption, (iii) “maxwellization” due to Coulomb

collisions. These mechanisms are shown to work ultimately for the global flattening of

PEC(r) profile: a lowering, in the plasma core, and a rise, in the periphery. The respective

results, in the case of transport of plasma’s self ECR only (i.e. no ECCD/ECRH), for

ITER-like and IGNITOR-like conditions will be presented.

REFERENCES

[1] Cherepanov K.V., Kukushkin A.B., (a) Proc. 31st EPS Conf. Plasma Phys. Contr.

Fusion. (London, U.K., 2004), ECA vol. 28(B), P-1.175; (b) Proc. 20th IAEA Fusion

Energy Conference. (Vilamoura, Portugal, 2004), TH/P6-56.

[2] Polevoi A.R., et. al., J Plasma Fusion Res. SERIES, 5 (2002) 82.

[3] Albajar F., Bornatici M., Cortes G., et. al., Proc. 31st EPS Conf. Plasma Phys. Contr.

Fusion. (London, U.K., 2004), ECA vol. 28(B), P-4.171; Proc. 20th IAEA Fusion

Energy Conference (Vilamoura, Portugal, 2004), TH/P4-18.


Effect of ECCD/ECRH-Produced Super thermal Electrons on Electron

Cyclotron Radiation Transpor t in Hot Tokamak Plasmas

K.V. Cherepanov, A.B. Kukushkin, L.K. Kuznetsova, E. Westerhof 1)

NFI RRC "Kurchatov Institute", Moscow, 123182, Russia, www.kiae.ru 1)FOM-Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM,

Trilateral Euregio Cluster, The Netherlands, www.rijnh.nl

The Fokker-Planck modeling of electron velocity distribution for ECRH and ECCD

showed the possibility of appreciable deviation from a Maxwellian for high enough

intensity of injected wave [1].

The contribution of superthermal electrons — for a model bi-maxwellian electron

velocity distribution (EVD) — to electron cyclotron radiation (ECR) transport in hot (Te >

10 keV) plasmas confined by a strong toroidal magnetic field (B > 5 T) was found [2] to

strongly influence the net ECR power loss profile PEC(r) (in particular, for ~10% fraction

with locally doubled temperature in the plasma core for ITER-like conditions, Te(0) ~ 25

keV). This qualitatively agrees with ASTRA + CYTRAN code-based analysis [3] which

showed significance of local/global contribution of ECR for purely maxwellian electron

velocity distribution (EVD) in steady-state ITER regimes with somewhat higher

temperatures (Te(0) ~ 35 - 45 keV).

The above suggests the necessity to evaluate the influence of ECCD/ECRH-produced

superthermal electrons on the ECR transport in hot tokamak plasmas. Here we present the

first results of evaluating the role of such superthermals. These include

(i) Fokker-Planck modeling of EVD for ECRH and/or ECCD numerical modeling for

hot tokamak plasmas, including ITER-like conditions and

(ii) subsequent modeling, with help of the code CYNEQ [2], of PEC(r) profile.

The work is partly supported by NWO-RFBR Grant Nr.047.016.016.

REFERENCES

[1] Harvey R.W., et. al., Phys.Rev. Letters, 62 (1989), p. 426.

[2] Cherepanov K.V., Kukushkin A.B., Proc. 31st EPS Conf. Plasma Phys. Contr. Fusion.

(London, U.K., 2004), ECA vol. 28(B), P-1.175.

[3] Albajar F., Bornatici M., Cortes G., et. al., Proc. 31st EPS Conf. Plasma Phys. Contr.

Fusion. (London, U.K., 2004), ECA vol. 28(B), P-4.171; Proc. 20th IAEA Fusion

Energy Conference (Vilamoura, Portugal, 2004), TH/P4-18.


Simulation of Heavy Impurities Transport and Radiation for ITER Scenarios

V.M.Leonov, V.E.Zhogolev

NFI, RRC « Kurchatov Institute », Moscow, Russia. Email: [email protected]

ABSTRACT

Last time attention is again attracted to the possibility of using high-Z materials in

reactors (tungsten for the divertor plates coating and argon for reradiation of some power).

In this case a danger of high-Z impurities accumulation in the plasma core is appearing. It

can reduce the discharge performance and decrease thermonuclear power.

Results of simulations of heavy impurities transport and radiation for ITER

reference operational scenarios are presented. Modeling has been done by ZIMPUR

impurity code with different suppositions about the impurity transport. This code was

integrated with the ASTRA transport code for the description of the bulk plasma behaviour

and with the NCLASS code to include neoclassical impurity fluxes in consideration. The

relative role of different components of the impurities fluxes is discussed.

Results of the modeling show, that the neoclassical thermal diffusion assists in a

plasma core screening from heavy impurities in all considered scenarios. Thus, a radiating

layer is formed on the plasma column periphery. The most pronounceable effect exists for

scenarios where the neoclassical impurity transport is waiting in the plasma core (for the

reversed shear scenario and for high-Z impurities in ELMy H-mode discharges). An

appreciable effect is indicated also for the inductive ELMy H-mode scenario for impurities

with lower Z, which are more strongly influenced by anomalous transport.

The calculated radiation near the plasma column edge approximately twice exceeds

the value calculated in the coronal approximation. This effect can be explained by the

reduction of impurity ions charge states at the charge exchange with deuterium/tritium

neutrals, which fuel the plasma.

Thus, the modelling shows, that effective radiation of power from the plasma

periphery is possible without the accumulation of heavy impurities in the plasma core for

considered ITER scenarios. It supports the possibility of using heavy materials in ITER.


Alpha-particle Confinement and Conservation of Second

Adiabatic Invariant

W.A. Cooper 1, M.Yu. Isaev 2, M.I. Mikhailov 2, J. Nuhrenberg 3, S. Okamura 4,

V.D. Shafranov 2, A.A. Subbotin 2, C. Suzuki 4, K. Yamazaki 4, R. Zille 3

1 CRPP, Association Euratom-Confederation Suisse, EPFL, Lausanne, Switzerland2 Russian Research Centre ”Kurchatov Institute”, Moscow, Russia

3 Max-Planck-Institut fur Plasmaphysik, IPP-EURATOM Association, Germany4 National Institute for Fusion Science, Oroshi-cho 322-6, Toki 509-5292, Japan

The improvement of α -particle confinement is one of the main targets in the processof optimization of stellarator systems. As was demonstrated earlier, long-time fast-particle collisionless confinement can be significantly improved in quasi-isodynamic(qi) [1] stellarators with poloidally closed contours of the magnetic field strength B

on the magnetic surfaces and in quasiaxi- and quasihelically-symmetric (qa and qh)stellarators with toroidally closed contours of B [2,3].

If these conditions (qi, qa, qh) are fulfilled exactly, then the second adiabatic in-variant, J =

∮V||dl is constant on a magnetic surface. On the other hand, it is known

that the conditions of quasi-symmetry cannot be satisfied exactly in the whole plasmavolume [4].

The investigations of fast particle confinement in tokamaks show that only a verysmall ripple (due to the finite number of toroidal field coils) is tolerable for good α -particle confinement, although the J contours are well behaved even for significantlylarger values of ripple components.

The behavior of J contours does not depend on the value of the magnetic fieldstrength. On the other hand, the shape of the particle drift trajectories stronglydepends on the gyro- to plasma-radius ratio. Thus, for configurations that are notexactly quasi-symmetric, it may occur that fast particles are not confined during thecollisionless drift motion even in configurations with closed contours of the secondadiabatic invariant.

In the present paper the correlation of α -particle collisionless confinement with thebehavior of contours of J for qi, qh and qa stellarator configurations is investigated.The problems of validity of the second adiabatic invariant during the motion of fastparticles in the plasma volume are discussed too.

References

[1] Gori S., Lotz W. and Nuhrenberg J. 1996 Theory of Fusion Plasmas (International

School of Plasma Physics) (Bologna: SIF) p. 335.

[2] J. Nuhrenberg, W. Lotz and S. Gori 1994 Theory of Fusion Plasmas (International

School of Plasma Physics) (Bologna: SIF) p. 3.

[3] J. Nuhrenberg and R. Zille, Phys. Letters A 129 No. 2 (1988) 113.

[4] D.A. Garren, A.H. Boozer, Phys. Fluids B 3 No. 10 (1991) 2822.


THE CHARGED PARTICLE DISTRIBUTION

FUNCTION in a TOKAMAK,

DEPENDENT FROM a VELOCITY GRADIENT.

Yu.V.Gott

Russian Research Centre Kurchatov Institute,

Kurchatov sq., Moscow, 123182 Russia

The particle distribution function deviation from equilibrium one will linearly

depends as on parameters from the factors breaking equilibrium distribution, such, as a

gradient of density, temperature, velocity etc. In standard neoclassical theory (SNT) the

corrections connected to a gradient of longitudinal and transverse velocities, were not taken

into account, as in SNT the magnetic field value on a magnetic surface was used. In this

work the magnetic field value on a drift surface was used and the correction to SNT

distribution function determined by radial gradients of longitudinal velocity and a magnetic

field are found.


Numerical study of high-frequency (ICRF) heating

at ど11-ぜ and とどぜ tokamaks.

N.B. Rodionov1, R.R. Khayrutdinov

1, A.A Ivanov

2,

1 TRINITI, Troitsk, Russia

2Keldysh Institute of Applied Mathematics, Moscow, Russia

Simulation of wave excitation and dissipation in Ion Cyclotron (ICRF) Range of

Frequencies in tokamaks T11-M and KTM at the regime of minority heating has been

carried out with the use of new program module [1]. Full wave 2D equation with anisotropy

susceptibility tensor and harmonic dependence in time and toroidal angle exp(inl - i】t) is

solved. In the frame of “cold” plasma model the numerical study of the high frequency

heating at T1-M on hydrogen minority in deuterium plasmas with lithium contamination less

than 4% has been carried out. ICRH heating has been applied on the main Ion-Cyclotron

frequency of hydrogen. The main attention has been focused on the role, which can play

addition of minority ion (for example, Li) on the efficiency of absorption of high frequency

power at hydrogen- deuterium plasma. Structure of fields and absorption profiles are

calculated. Detailed comparison with experiment is provided.

At this work a study of the ICRH heating at the regime of minority addition for

KTM tokamak is also carried out. This device has aspect ratio ん=2, elongation k=1.7 and is

located at the region between low and moderate aspect ratio tokamaks, what applies

peculiarity on excitation of high frequency harmonics. At presented work, numerically, for

different parameters of plasma and tokamak the most effective scenario of high frequency

heating for these devices is determined.

1. Khayrutdinov R.R., Ivanov A.A. Medvedev S. Yu, Rodionov N.B.

New RF heating module of the tokamak plasma in the frame of DINA code. 31st European

Physical Society Conference on Plasma Physics, june to 2nd

2004, Imperial College London,

P1-177. Europhisics Conference Abstracts vol. 28G.


Numerical investigation of a tokamak used as the volumetric neutron

source for material tests

A.A. Azizov, G.G. Gladush, V.N. Dokuka, R.R. Khayrutdinov

SSC RF TRINITI, Troitsk, Russia

The ITER project is a fundamental approach towards creation of fusion energetics. It

is expected to demonstrate practicability of ignition and continuous burning of controlled

fusion reaction. However, ITER is incapable of resolving the problems of radiation resistant

materials, development and testing of systems and components ensuring the required

operation life for DEMO conditions and subsequent fusion reactors. Earlier, a new concept

for the volumetric neutron source on the basis of the tokamak with the aspect ratio of A=2

was suggested for transmutation of minor actinides. This work is aimed to develop a scheme

for a compact tokamak suitable for testing of materials and structural components of DEMO

and subsequent reactors. The concept of the CTF reactor is based on the latest experimental

data from NSTX, MAST, GLOBUS-M and ITER data base. The numeric analysis was

carried out utilizing the 1.5D code DINA. The complex scenario for current ramp is

analyzed. It is assumed that about 30-50% of the current ramp-up is provided by means of

the central solenoid. In this case a half of possible poloidal flux is utilized. After the current

ramp-up is completed the inductor can be removed from the system. The numeric simulation

demonstrated that when the current plato is reached its maintenance is possible by means of

the bootstrap-current and current drive from neutrals injection. The ion temperature is shown

to reach up to 14-15 keV at the neutron energy about 400 keV and flux power of 50MW. For

plasma density of 1.5 1020 m3 this provides intensive fusion reaction and the average neutron

flux onto the blanket of about 1.3 MW/m2. The maximum neutron load in the test region is 2

MW/m2. Under this conditions and at R=2 m and a=1 m the plasma current is within the

range of 5-10 MA and QÃ4.8. These parameters are achieved at くNø5.8 and the confinement

enhancement factor being less than 2.5.

The magnetic system of the CTF tokamak utilizes the warm solenoids. The power of

the solenoid currents must be about 100 MW. The numerical analysis demonstrated that the

heat load on the outer divertor plates is in the range of 10-15 MW/m2 at the tilt angle of 15-

200. The latter fact provides the possibility for testing of the divertor components under

conditions of the fusion reactor.


Influence of electric fields on the energetic particle orbits in

stellarators

A. V. Tykhyy

Institute for Nuclear Research, Prospekt Nauky 47, 03680 Kyiv, Ukraine

Good confinement of energetic particles is important for fusion systems. It is known

that trapped particles are often much worse confined than the passing ones, in par-

ticular in classical stellarators they are lost over just one orbital period. Such losses

would preclude thermonuclear application, therefore modern stellarators employ quasi-

symmetry (CHS-QA, NCSX) or finite beta effects (Wendelstein 7-X) to improve the

confinement of energetic particles [1].

Electric field may produce an influence on particle orbits similar to the influence

of plasma pressure [2]. A simple estimate gives Er ∼ T/(ea) ∼ 5kV/m in the whole

plasma volume of W7-X when T = 2 ÷ 3keV, while in transport barriers the electric

field can be much stronger. The effect of electric field on particle orbits in tokamaks

and classical stellarators was considered analytically in Ref. [3]. However, only the

helical and toroidal harmonics of the magnetic field were taken into account. More

recently, the case of Wendelstein-line stellarators was investigated in Ref. [2] by means

of a simple analytical model for well-trapped particles in the core plasma and by

orbit simulation. It was shown that negative radial electric fields generally improve

confinement, while positive fields have an adverse effect.

In this paper, we extend the analytical results of Ref. [2] to include locally passing

and marginally trapped particles. We study the influence of electric field on the

bounce-averaged orbits of locally trapped and locally passing particles in the core

plasma regions of W7-X. We also analyze the bounce-averaged motion of particles in

localized electric fields, which occur in internal transport barriers. Finally, we discuss

the influence of electric field on stochastic diffusion associated with the presence of

transitioning particles [4].

[1] W. Lotz, P. Merkel, J. Nuehrenberg, E. Strumberger, Plasma Phys. Contr. Fusion 34,

1037 (1992).

[2] Ya. I. Kolesnichenko et al., 31st EPS Conf. on Plasma Phys., London, ECA 28G,

P1.201 (2004).

[3] Itoh K., Itoh S-I., Plasma Phys. Contr. Fusion 38, 1 (1996).

[4] C. D. Beidler et al., Phys. Plasmas 8, 2731 (2001).


Analysis and interpretation of observations of Alfvénic activity

in Wendelstein 7-AS

Ya.I. Kolesnichenko1, V.V. Lutsenko1, A. Weller2, A. Werner2, Yu.V. Yakovenko1,

J. Geiger2, S. Zegenhagen2, A. Tykhyy1

1 Institute for Nuclear Research, Kyiv, 03680, Ukraine2 Max-Planck-Institut für Plasmaphysik, D-17491 Greifswald, Germany

This work continues a series of our works aimed to explain various energetic-ion-induced

Alfvén instabilities observed in experiments on the W7-AS stellarator (a number of these in-

stabilities observed before 2001 are described in an overview [1]). Earlier it was shown that

a temporal evolution of the Alfvén velocity leads to the consecutive destabilization of various

Alfvén modes, which explains strong successive changes of the frequencies of destabilized

modes (see Ref.[2] and an overview [3]). Later it was shown that gaps in Alfvén continuum

correlate with observed frequencies, and an explanation of the fact that a very small increase of

the plasma density (<15%) can result in the disappearance of Alfvénic activity was suggested

[3-5]. Recently it was predicted that a monochromatic wave can enhance the electron thermal

conductivity, which explains strong drops of the plasma energy content during the instability

bursts of [6,7]. In this work, we carry out a comparative analysis of various W7-AS shots with

Alfvén instabilities. This is actually an attempt to understand why Alfvénic activity in different

shots was qualitatively different (quasi-steady-state or bursting, affecting the confinement of

the injected ions and even the confinement of the bulk plasma energy or having no influence on

the confinement) and why no instability occurred in some shots although the same neutral beam

injection was used. Note that to understand different manifestations of Alfvén instabilities in

W7-AS is also of importance for making reliable predictions on the role of Alfvén instabilities

in next-step Wendelstein-line stellarators (W7-X and a Helias reactor).

References

[1] A. Weller et al., Phys. Plasmas8, 931 (2001).

[2] V.V. Lutsenko et al., Report TH/P3-16 at the 19th IAEA Conference, Lyon (2002).

[3] Ya.I. Kolesnichenko et al., Fusion Science and Technology46, No.1, 54 (2004).

[4] A. Weller et al., Plasma Phys. Control. Fusion45, A285 (2003).

[5] J. Geiger et al., Fusion Science and Technology46, No.1, 13 (2004).

[6] Yu.V. Yakovenko et al., Report TH/P4-48 at the 20th IAEA Conference, Vilamoura

(2004).

[7] Ya.I. Kolesnichenko et al., submitted to Phys. Rev. Lett. (2005).


Impact of structural inhomogeneity on waves in a 2D complex plasma

S.K. Zhdanov, D. Samsonov, G.E. Morfill

Max-Planck Institute for Extraterrestrial Physics, D-85741 Garching, Germany

Monolayer hexagonal plasma crystals are formed of monodisperse plastic microspheres

levitated in a sheath of a radio-frequency discharge. They can sustain linear and nonlinear

waves. Using a molecular dynamics simulation we study the effects of the lattice

inhomogeneity at different scales on wave propagation. There are three scales of spatial

inhomogeneity in a plasma crystal, which affect the wave propagation: the scale of global

lattice inhomogeneity due to the confinement potential [1], the characterictic size of the defect

clusters, and the average interparticle distance. The global lattice inhomogeneity (of the lattice

number density) makes the phonon speed variable and it can induce the wave front curvature

[2] and cause wave steepening at the edge of the crystal ("tsunami effect"). Defect clusters

(with a size of up to tens of lattice cells) can scatter waves due to local structure variations. The

local crystal structure at the level of an individual lattice cell is responsible for the anisotropy of

the short wave length wave propagation. Nonlinear compressional waves of sufficiently high

amplitude produce defects and locally melt the lattice [3]. Wave-induced defect groups

propagate with the wave and form correlated wave structures or focusons. We demonstrate that

focusons tend to propagate along the lines of close packing in a monolayer hexagonal lattice

amplifying the anisotropy of wave propagation.

References

[1] S. Zhdanov, R.A. Quinn, D. Samsonov and G.E. Morfill, NJP 5, 74 (2003)

[2] S.K. Zhdanov, G.E. Morfill, D. Samsonov, M. Zuzic and O. Havnes, PRE 69, 026407

(2004)

[3] D. Samsonov, S.K. Zhdanov, R.A. Quinn, S.I. Popel and G.E. Morfill, PRL 92, 255004

(2004)


Large-amplitude oscillations of dust par ticles in a plasma sheath

A. A. Samarian and S. V. Vladimirov

School of Physics, The University of Sydney, New South Wales 2006, Australia

In laboratory experiments, the micrometer sized highly charged dust grains levitate in

the sheath region of a horizontal negatively biased electrode where there is balance between

the gravitational and electrostatic forces acting in the vertical direction as well as an

externally imposed confining potential applied in the horizontal plane. The particle

confinement involves the gravity force and the electrostatic force acting on the dust particles

with variable charges, and is a complex process exhibiting oscillations, disruptions and

instabilities of particles [1,2]. A characteristic feature of the particle confinement is also the

strong influence of plasma collective processes such as the plasma wake. Due to the many

factors affecting the dust particle motion, various nonlinear phenomena can appear.

Here, we investigate large-amplitude oscillations of dust particles levitating in an rf

plasma sheath. Different cases of various relations between the oscillation amplitudes are

observed. In particular, specifically designed shapes of the confining potential are applied to

elucidate the characteristics of the particle nonlinear motions.

Vertical oscillations take place when the horizontal confining potential is strong; they

are triggered by changing the input power. The oscillation amplitudes are about a few

interparticle distances, with relatively high frequencies corresponding to the frequency range

from 30 Hz to 100 Hz and high oscillation energy exceeding 100 eV. The coupling between

the horizontal and vertical motions of dust particles is discussed. Experiments are completed

by theoretical modeling where the oscillation modes in the system of two dust particles is

observed and analyzed. The study performed can serve as a basis for further investigation of

finite-amplitude collective phenomena in structures consisting of a number of dust particles,

such as nonlinear wave and soliton formation in chains of dust particles.

[1] S.V. Vladimirov and A.A. Samarian, Phys. Rev. 65, 046416 (2002)

[2] A.A. Samarian, S.V. Vladimirov, and B.W. James, Phys. Plasmas 12, 022103 (2005).


A Boundary Structure of Dusty Cloud.

A.V. Zobnin

Institute for High Energy Densities, Russian Academy of Sciences,Izhorskaya, 13/19, Moscow, Russian Federation.

Self-organization and self-structuring properties of complex plasmas led to

various shapes of dusty clouds observed in experiments. Boundaries of clouds are

sharp. An analysis of boundary stability could explain a form of dusty cloud usually

and equilibrium dust particle density. An analysis of the stationary dust-void

boundary in a simple flat geometry is presented. The balance of electrostatic, ion drag,

thermophoretic, and gravitation forces acting on dust grains governs stability of dusty

cloud. Presented model includes a ionization, recombination on dusty particles,

diffusion, and drift of ions in electric field. The solutions for dusty-free region and for

dusty cloud boundary layer are joined by condition of continuity of ion and electron

concentrations and electric field. A Possibility of joining connects ion and electron

flux on the boundary with parameters of dusty particles and determines position of the

dusty cloud in discharge.


Lydia Johnson, Beatrice Maria Annaratone, A. G. Khrapak, H. M. Thomas, and G. E. Morfill

Max-Planck Institut fuer Extraterrestrische Physik, D-85741, Garching, Germany

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Dust-lattice waves: Role of charge variations and anisotropy of dust-dust

interaction

R. Kompaneets1,2, A.V. Ivlev1, V. Tsytovich1,3, G. Morfill1 1 Max-Planck-Institut für extraterrestrische Physik, Garching, Germany

2 Moscow Institute of Physics and Technology, Dolgoprudny, Russia 3 General Physics Institute of the Russian Academy of Sciences, Moscow, Russia

Dust-lattice waves are studied in the framework of the 1D particle string model. The dust-

dust interaction potential is assumed to have an arbitrary dependence on the vertical and

horizontal coordinates, which allows to take into account the wake field effects. Both

vertical and horizontal charge variations are also included into the model. The model yields

the coupling between the vertical and horizontal (longitudinal) modes: the coupling

coefficient is the sum of 6 terms, each caused by a different physical mechanism. It is

shown that the coupling can trigger the resonance oscillatory instability, which has been

already observed in experiments. It is also shown that a non-oscillatory instability can

appear at small wavenumbers due to the coupling.


The reactive ion-drag force in dusty plasmas

S. A. Maiorov

A.M. Prokhorov Genera Physics Institute, Russian Academy of Sciences,

Moscow, 119991 Russia

We consider here a new effect, namely, the appearance of a reactive force

accelerating the dust particle against the ion flow. The mechanism of the occurrence of

reactive force accelerating a dust particle against an ion flow is discussed. It is based on

momentum transfer from an ion flow additionally accelerated in the dust grain field to the

buffer gas atoms (upon charge exchange of an ion on buffer gas atoms). As a result, from the

ions + dust grain system the atoms (that were ions before a resonance charge exchange

collision) take off a larger momentum than they had brought in, which creates a reactive

force directed against the flow (negative friction force).

The mechanism of this force rests on collisions of ions of the flow with buffer gas

atoms and on the momentum transfer from the flow of ions to the buffer gas atoms (upon

charge exchange of ions on buffer gas atoms). Note that there is a great difference between

the negative friction force that acts in the direction increasing the relative velocity of

motion and the negative differential friction force that corresponds to a decrease of the

friction force with increasing velocity of motion, but acts in the direction typical of the

friction force.

The friction force due to ion-atom collisions with charge exchange is analyzed for

the first time in the present paper. The magnitude of this force is evaluated. The main

consequence of the obtained estimate of the reactive friction force is its sign. The friction

force is directed against the ion flow incident on the dust particle, i.e., under the action of

such a friction force the dust particle speeds up against the ion flux. Another interesting

consequence of the obtained estimate is that the friction force is independent of the ion

flow velocity and that the largest contribution to the reactive force is made by far flights.

The situation is analogous to the friction force due to Coulomb collisions.


Attractive force in 3D plasma clusters

T. Antonova, B. M. Annaratone, H. M. Thomas and G. E. Morfill

Max-Planck Institut fuer Extraterrestrische Physik, D-85740, Garching, Germany

The nature of forces responsible for the structured system of particles in plasma still is not

explained theoretically. In this contribution we present measurements of the interaction

force between particles in three-dimensional plasma clusters in weak external

confinement. The particles settle in the vicinity of secondary plasma, which is produced

above one segment of the “adaptive” electrode. This is used as triode in an RF reactor

driven at 13.56 MHz. Clusters from 4 up to 73 particles have been obtained at the

pressure of 57, 65 and 76Pa. The structure of big clusters shows sub-parts in icosahedral

geometry, the cluster of smaller size (17 particles) has fcc structure. But in the

disagreement with the pair short-range interaction the inner shell is always empty. The

attractive and repulsive forces have been derived from the kinematics of the motion inside

the clusters. Due to a unique three-dimensional diagnostic we can get the coordinates and

the velocities of all the particles simultaneously. The motion of particles inside the

clusters of 17 particles at pressure 76Pa and 4 particles at 57Pa has been studied in detail.

It was not externally stimulated; we just recorded the spontaneous/thermally excited

behaviour. One particle in the 17 particles’ cluster is pushed by another, just arrived to the

top of structure from the above 2D cloud. The hit particle has an unstable position and

moves in order to find equilibrium. During this motion it also pushes and re-arranges

neighbouring particles, but does not go inside the structure. Finally, after 1.12sec this

particle comes back to the external shell. The value of the force, which acts between

particles in these two clusters, and the distances of the acting were obtained

approximately the same. The difference in pressure (57 and 76Pa) is compensated by

different voltage on the RF driven electrode (300 and 200V peak to peak, respectively),

that allows to keep Debye length. We have never observed the particles to form vertical

chains as seen frequently in the standard plasma sheath. For small distances a Coulomb

repulsion, more or less screened, is largely accepted. The attractive force could be due to

self-induced shadow force or to a partial dipole component due to an ion 'wake'.


Coulomb Clusters: Stability and Spectrum of Energy States

F.M. Cheung, C. Brunner, S. Barkby, A.A. Samarian, B.W. James

School of Physics, The University of Sydney, NSW 2006, Australia

Coulomb cluster is a phenomenon in classical physics which is under substantial amount of

attention. These clusters are characterized by the strong electrostatic interaction of highly

charged particle trapped within an external confining potential. Examples of such systems

include ion traps and quantum dots. Investigation in this area had been further encouraged

in the past few decades with the discovery of complex (dusty) plasmas and the increase in

the computer simulation of complex plasma experiments. In discharge complex plasma

system, micron-sized dust particles which are highly negatively charged (~104e) repel each

other under strong coulomb forces to arrange themselves into well ordered structures. Such

structures with limited number of particles are referred as Coulomb clusters in dusty

plasma.

In this study, stability of dust clusters with different numbers (2 to 12) of micron-sized

particles levitated in a horizontal plane was investigated experimentally in inductively

coupled magnetised dusty plasma. When the magnetic field was absent, the clusters

exhibited small random fluctuation but always remained around their equilibrium position.

It was found that the fluctuating motion of the particles was dominated by its azimuthal

component which was 2-12 times larger than radial component. It was also observed that

the number of particles in a cluster strongly influenced the cluster instability. The reason

behind certain cluster structures being more unstable than others was likely to be due to

their number of possible metastable states. It was observed that the stability of individual

particles within the clusters increased with increasing axial magnetic field

The experiments where complemented by numerical study and dynamic of coulomb cluster

systems are simulated on a computer for various particle numbers. The system is modelled

using electrostatic confinement from a potential well, classical coulomb repulsion, friction

force and a stochastic force. Classical force equations are used to simulate the behaviour of

highly charged dust particles in such a field. Our model allowed us to predict the structural

configuration of the dust cluster under particular experimental conditions and the results are

symmetrical clusters with concentric shells with multiple stable (metastable) states (referred

to as packing sequences). It was shown that configuration of Coulomb clusters depends on

friction force (pressure). A simple explanation based on limited-time metastable states

approach was proposed. Spectrum of energy states of dust Coulomb clusters corresponding

to various packing sequences was obtained. The broadening of the spectrum due to

inter-shell rotation was discovered.


Effect of ion-neutral collisions on particle charge in gas-discharge plasmas

S. Khrapak,1 S. Ratynskaia,1 A. Zobnin,2 V. Yaroshenko,1 M. H. Thoma,1 M. Kretschmer,1

A. Usachev,2 H. Höfner,1 G. Morfill,1 O. Petrov,2 and V. Fortov2

1 Max-Planck-Institut für extraterrestrische Physik, D-85741 Garching, Germany2 Institute for High Energy Densities, Russian Academy of Sciences, Izhorskaya 13/19,

125412 Moscow, Russia

The particle charge is one of the most important parameters of complex plasmas. In gas

discharges the (negative) charge on a grain is determined bythe balance of electron and ion

fluxes to its surface. To calculate these fluxes the collisionless orbital motion limited (OML)

theory is usually used on the basis that ion and electron meanfree paths i(e) are typically

long compared to the plasma screening lengthλD. However, theory has shown that ion-neutral

charge-exchange collisions in the vicinity of a small probeor dust grain can lead to a substantial

increase in the ion current to their surfaces even when`i is larger thanλD [1, 2, 3]. This can

considerably suppress the grain charge.

An experimental determination of particle charge in a bulk dc discharge plasma covering a

wide range of neutral gas pressures, was recently reported [4]. The charge was obtained by two

independent methods: One based on an analysis of the particle motion in a stable particle flow

(force balance method) and another on an analysis of the transition of the flow to an unstable

regime (linear dispersion relation method). Results of both experimental methods were in good

agreement. The charges obtained were several times smallerthan predicted by the collisionless

OML model, which was attributed to the effect of ion-neutralcollisions.

In the present paper we report new experimental results obtained with particles of different

sizes. The measurements are compared with molecular dynamics simulations of particle charg-

ing for conditions similar to those of the experiment, with other available experimental data on

particle charge in the bulk of gas discharges, and with a simple analytical model accounting for

ion-neutral collisions. All the considered evidence indicates that ion-neutral collisions represent

a very important factor, which significantly affects (reduces) the particle charge under typical

discharge conditions.

References

[1] A. V. Zobnin, A. P. Nefedov, V. A. Sinel’shchikov, and V. E. Fortov, JETP91, 483 (2000).

[2] M. Lampe, V. Gavrishchaka, G. Ganguli, and G. Joyce, Phys. Rev. Lett.86, 5278 (2001).

[3] M. Lampeet al., Phys. Plasmas10, 1500 (2003).

[4] S. Ratynskaiaet al., Phys. Rev. Lett.93, 085001 (2004)


The “trampoline effect” – distribution of forces inside the void region of

a complex plasma in microgravity

M. Kretschmer, S. Khrapak, S. Zhdanov, H. Thomas, G. Morfill, the PKE-Nefedov team

Max-Planck-Institut für Extraterrestrische Physik, D-85741 Garching, Germany

The PKE-Nefedov facility allows the study of complex (dusty) plasmas under micro-

gravity conditions onboard the International Space Station (ISS) [1]. In the experiments, the

micro-particles can form regular structures (e.g., plasma crystals) inside the bulk of a rf

discharge plasma. In most of the experiments the particles do not fill the entire plasma

volume, but a particle-free region in the central part of the discharge - the so called “void”-

is formed. It is believed that the main process responsible for the void formation is the ion

drag force, which can exceed the electric force in the limit of weak electric fields and,

hence, pushes the dust particles out of the central region of a discharge.

In the experiments performed at low gas pressure (p=12 Pa) an instability of the dust

cloud–void interface was observed. The instability was accompanied by periodic

contractions of the void volume and fast injection of relatively small number dust particles

inside the void region (what we call here “trampoline effect”). In the next (“relaxation”)

stage the injected particles were pushed from the void back into the particle cloud. This

relaxation stage was much slower than the injection. The cycle fast injection – slow

relaxation then repeated periodically.

We were able to perform an accurate analysis of particle trajectories during the

relaxation stage. From this analysis the distribution of forces acting on the particles inside

the void region was reconstructed. Due to relatively low neutral gas pressure used in the

experiments the direct comparison with the recent theoretical models of the ion drag force

(in collisionless limit for ions) and of the void formation is possible. Such a comparison

was performed and good agreement with theoretical predictions was found. The obtained

results provide a clear picture of the nature of the void formation in complex plasmas under

microgravity conditions.

[1] PKE-Nefedov Homepage, http://www.mpe.mpg.de/pke


Study of Relation between Transpor t Coefficients in Dusty Plasma Systems

V. E. Fortov1, O. S. Vaulina

1, O. F. Petrov

1, I. A. Shakhova

1,

A. V. Gavrikov1, N.A. Vorona

2

1Institute For High Energy Densities RAS, Moscow, Russia 2Moscow Institute of Physics and Technology, Moscow, Russia

Transport coefficients (including self-diffusion, and viscosity constants) are fundamental

dynamic parameters that reflect the nature of the interparticle potentials and characterize

thermodynamics of the systems. The determination of analytical relations for transport

constants in strongly correlated systems can be useful for application of known hydrodynamic

approaches in analysis of wave propagation, shear flows, and formation of different

instabilities.

New data on transport constants were obtained for dust particles in weakly ionized plasma.

The numerical simulations shown that the shear viscosity and diffusion constants are

determined by the value of effective coupling parameter ゎ*, and to take into account the

energy dissipation due to the collisions of dust particles with the neutrals of surrounding gas

the scaling factor z must be used. In wide rage of ゎ* the shear viscosity constants may by

presented in form of Einstein—Stokes relation with the constant radius of cross-section for

interparticle collisions. The analytical approximation for shear viscosity and diffusion

coefficients in strongly correlated dust structures (ゎ* > 40) was proposed.

The numerical results are in an agreement with direct measurements of viscosity in dusty

plasma of rf- discharge, and with the determinations of shear viscosity constants from

Einstein—Stokes relation and diffusion measurements under different experimental

conditions. We can estimate of the shear viscosity constants for studied dust-plasma systems

in a wide range of coupling parameters (ゎ* ~ 25-82) as ~ 0.4-14 Pa s. This difference can be

result from the appreciable difference between the dusty structure parameters (dust

concentrations, kinetic temperatures, and particle mass) in analyzed experiments.


Forces and effective potential energy inside the void region of a complex

plasma in microgravity

M. Kretschmer, U. Konopka, S. Zhdanov, the PKE Nefedov Team

Max-Planck-Institut für extraterrestrische Physik (MPE), 85741 Garching, Germany

Since 2001, the PKE-Nefedov facility allows to perform complex (dusty) plasma

experiments under microgravity conditions onboard the International Space Station ISS [1].

Micron-sized particles in the center of a RF discharge form big three-dimensional strongly

coupled Coulomb systems (‘plasma crystals’), but in most experiments a particle-free

region in the center is observed, the so-called ‘void’. The cause for this void is not quite

clear, but the ion drag force that overcomes the small electric field in the center is

suspected. Unfortunately, there are no particles inside the void to give us information about

the conditions inside.

In the experiment described here we pushed particles into the void where they were

expelled immediately. From the trajectories at different gas pressures we could derive the

forces (and a ‘potential energy’) acting on the particles inside the void. Together with

numerical simulations (see figure below), this might help to identify finally the mechanism

that forms the void.

Parabolic fits of trajectories of particles inside the void at a pressure of 61 Pa. Axes are in mm.

[1] PKE-Nefedov Homepage, http://www.mpe.mpg.de/pke


Interaction between grains in plasma

S. A. Maiorov

A.M. Prokhorov Genera Physics Institute, Russian Academy of Sciences,

Moscow, 119991 Russia

We consider here a new effect, namely, the appearance of a repulsion force between

dust grains due to ions collisions. The mechanism of this force rests on collisions of bound

ions with buffer gas atoms and on the momentum transfer by atoms (that were ions before a

resonance charge exchange collision). This force is an inverse square force, like the

Coulomb force. The mechanism of the occurrence of recombination force is discussed first

time in the present paper. The magnitude of this force is evaluated.


Reabsorption of Langmuir waves generated by a hot electron beam

propagating in a plasma

G.R. Foroutan1;2, S. Sobhanian2, B. Li1, P.A. Robinson1, I.H. Cairns1, M. Moslehi-Fard2

1School of Physics, The University of Sydney, NSW 2006, Sydney, Australia2 Faculty of Physics, Tabriz University, Tabriz 51664, Iran

The propagation of a cloud of hot electrons in a plasma and generation of Langmuir waves are

investigated using numerical simulation of quasilinear equations. It is shown that for an initially

stable hot electron beam instability proceeds as a result of advection and generated Langmuir

waves are completely reabsorbed by next arriving slower electrons and reabsorption is maximal

near the upper velocity boundary of the plateau at the electron distribution function. However,

for unstable injection of the beam a part of waves fails to be reabsorbed and remains at the

site of injection. The level and spatial extent of these waves depends on the slope of the initial

distribution function. For multi-beam injection the number of regions at the site of injection

with high level of waves, depends on the temperature of the beams and their separation in the

velocity space.


On the transformation of structurally unstablemagnetic configuration into structurally stable one

D. P. Kostomarov1, S. V. Bulanov2, I. N. Inovenkov1, E. Y. Echkina1

1Faculty of Computational Mathematics and Cybernetics, Moscow State

University, Moscow, Russia, [email protected], [email protected]

2A. M. Prokhorov Institute of General Physics, RAS, Moscow 119991,

Russia [email protected]

Reconnection of magnetic field lines plays a key role in various problemsof physics of space and laboratory plasmas including the disruption instabil-ity the nonlinear evolution of magnetic islands in tokamak plasmas and solarflares. A rapid change of magnetic field topology during magnetic reconnec-tion is closely related to a problem of vector field structurally stability.

It this work the nonlinear dynamics of magnetohydrodynamic perturba-tions in structurally unstable magnetic configuration is studied numerically.It is shown that these perturbations cause the electric current to evolve non-linearly in such a manner that a structurally unstable configuration of themagnetic field transforms into a structurally stable configuration. Such atransformation is forbidden in ideal magnetohydrodynamics but occur in theprocess of magnetic field line reconnection.

The authors of this work created the nonlinear parallel 3D-MHD codemaking possible to use grid with small space steps for numerical simulationof current sheets formation and magnetic reconnection.

The reuslts of 3D-MHD computer simulation of transformation of struc-turally unstable 2D and 3D magnetic configurations with high order crit-ical points into structurally ones are presented. We have investigated thetransformations induced by a finite amplitude electric current excited in theplasma under the action of imposed electric field at the boundary. The behav-ior of plasma density, pressure and the electric current density is consideredin details.


Propagation of finite amplitude disturbances

in an inhomogeneous magnetized plasma

Francesco Califano1,2, Laura Galeotti2, Maurizio Lontano1

1 Istituto di Fisica del Plasma, C.N.R., EURATOM-ENEA-CNR Ass., Milano, Italy

2 Universita di Pisa and INFM, Pisa, Italy

The evolution of electromagnetic waves injected from the boundary in a inhomoge-

neous magnetized collisionless plasma is investigated by means of a kinetic numerical

code. We use the Harris pinch magnetic configuration as the supporting medium

for wave propagation.

The numerical code solves the Vlasov equation for ions and electrons in the

1D - 2V phase space, self consistently coupled to the Ampere and to the Faraday

equations. The magnetic field is unidirectional. Open boundary conditions are used

to inject the waves from outside at a given frequency, while the wavelength is selected

self-consistently by the system.

The aim of the work is to study the interaction of the injected waves with the

upper hybrid resonance and/or with the cut off. The induced excitation of elec-

tric and magnetic fluctuations and the competition between electromagnetic and

electrostatic effects are discussed.


Role of numerical dissipative effects

in collisionless plasmas simulations

Francesco Califano1,2 and Laura Galeotti1

1 Universita di Pisa and INFM, Pisa, Italy

2 Istituto di Fisica del Plasma, C.N.R., EURATOM-ENEA-CNR Ass., Milano, Italy

We present Vlasov-Poisson numerical simulations of the two-stream instability and

of the nonlinear Landau damping problem. We show that (numerical) dissipative

effects at the grid length scale can have important feedback on the macroscopic

evolution of the system. This result is obtained despite the dissipative scale length is

much smaller than any macroscopic physical scale length of the system. A discussion

on different algorithms used to integrate numerically the Vlasov equation is included.


Sheath formation in a two-electron temperature plasma

T. Gyergyek1, M. Cercek2,3

1 University of Ljubljana, Faculty of electrical engineering, Tržaška 25, SI-1000 Ljubljana,

Slovenia2 Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana Slovenia

3 University of Maribor, Faculty of civil engineering, Smetanova 17, SI-2000 Maribor,

Slovenia

Plasma potential formation in front of a floating electron emitting electrode (collector) is

treated by a simple, one-dimensional fluid model. It is assumed that the distribution function

for the electrons is a two-temperature Maxwellian. The electrons with the lower temperature

are called the cool electrons and the electrons with the higher temperature are called the hot

electrons. The ions are assumed to be monoenergetic and at rest at a large distance from

the collector. Emitted electrons are also monoenergetic and they leave the collector surface

all with the same nonzero initial velocity. The flux of the emitted electrons is proportional

to the flux of incoming cool and hot electrons. The proportionality constant is called the

emission coefficient. We assume that the relation between the density of the hot and of

the cool electrons and the plasma potential in the sheath and pre-sheath region is given by

the Boltzmann relation. We also assume that the flux and the energy of the particles are

conserved. Based on these assumptions three equations can be derived: 1) the zero electric

field condition at the collector, which is fulfilled, when the emission of electrons from the

collector reaches critical level, 2) the expression for the zero total current to the floating

collector and 3) the modification of the Bohm criterion due to the presence of the hot and of

the emitted electrons in the system. If the ion mass, the hot to cool electron density ratio and

the hot to cool electron temperature ratio are selected these 3 equations can be solved for

the potential drop in the sheath of the floating collector, the Mach number and the critical

emission coefficient. In some cases the system of equations has 3 solutions and in some

cases even 5 solutions. The nature of these solutions is briefly discussed.


Weibel instability due to the inverse bremsstrahlung absorption

K. Bendib-Kalache, A. Bendib, K. Mohammed EL-Hadj and A. Tahraoui

Laboratoire Electronique Quantique, Faculté de Physique, USTHB, BP 32 El-Alia,

16111 Bab Ezzouar Alger, Algérie.

The Weibel instability analysis due to the inverse bremsstrahlung absorption source

including the electron-electron collisions is presented. The Fokker-Planck equation for the

electron in homogenous plasma in the presence of high frequency electric field has been

numerically solved. The electron-electron and the electron-ion Landau operators have been

used to describe the collision processes. Using the super Maxwellian isotropic distribution

function

− mvexp~ [1] where 52−=m , the second anisotropic distribution function has

been numerically computed for arbitrary Z value. The results have been used to study the

stability of the collisionless Weibel modes. It has been shown that the growth rates of the

Weibel modes due to the bremsstrahlung source are significantly reduced when the

electron-electron collisions are accounted for.

[1] J. P. Matte, M. Lamoureux, C. Moller , R. Y. Yin, J. Delettrez, J. Virmont and T. W.

Johnston, Plasma Phys. Controlled Fusion 30, 1665 (1988).


Effects of the magnetic field and the thermal electron motionon

characteristics of guided-wave-sustained plasmas

Suwon Cho

Department of Physics, Kyonggi University, Suwon, Korea

The magnetic field and the electron thermal motion are considered in studying the charac-

teristics of guided-wave-sustained plasmas. Using the fluid model, the generalized Ohm’s law

is derived for a warm non-uniform magnetized plasma and is used to obtain the governing

equation for electromagnetic waves in a plasma-loaded waveguide. To efficiently trace all the

modes existing in a bounded plasma, the differential wave equation is converted into a matrix

eigenvalue equation, from which the dispersion relation isfound numerically.

The magnetic field causes the cold plasma column resonance tooccur at a higher frequency

or a lower plasma density. The resonance frequency is obtained analytically using the electro-

static approximation and its validity is justified by comparison with the exact numerical solu-

tions of the electromagnetic wave equation. When the electron cyclotron frequency is lower

than the wave frequency, the electron temperature term separates the degenerate electrostatic

modes near the upper hybrid resonance, and the inhomogeneity of the radial density brings

them to shift toward the higher density region in the phase diagram and to couple with the

Trivelpiece-Gould (TG) mode in a collisional plasma. It is also shown that the TG-mode is the

only wave allowed at the electron cyclotron resonance condition and that numerous volume

waves appear but they do not couple with the TG-mode at a higher magnetic field. Finally,

the influence of the electron thermal motion and the magneticfield on the axial structure is

examined.


A fully implicit 3D extended MHD algorithm

L. Chacón1

1Los Alamos National Laboratory, Los Alamos, NM 87545, USA

Extended MHD (XMHD) includes nonideal effects such as nonlinear, an-isotropic trans-

port and two-fluid (Hall) effects. XMHD supports multiple, disparate time scales that make

explicit time-differencing approaches extremely inefficient. While a fully implicit implementa-

tion promises efficiency without sacrificing numerical accuracy [1], the nonlinear nature of the

XMHD system and the numerical stiffness of its fast waves make this endeavor very difficult.

Newton-Krylov methods are, however, ideally suited for such a task. They combine Newton’s

method for nonlinear convergence and Krylov techniques to solve the associated Jacobian (lin-

ear) systems. Krylov methods can be implemented in a Jacobian-free fashion (avoiding forming

and storing the Jacobian matrix), and can be preconditioned for efficiency [3, 4]. The precon-

ditioning step considers an inexpensive approximation to the Jacobian inverse to enhance the

Krylov iteration convergence rate, and can be easily incorporated into the Krylov algorithm.

The focus of this work is two-pronged. On the one hand, we will discuss a novel second-

order finite-volume discretization [2] for implicit 3D MHD, applicable to general curvilinear

geometries that is: 1) conservative, 2) solenoidal inB andJ, 3) numerically non-dissipative,

and 4) linearly and nonlinearly stable. On the other hand, we will discuss our preconditioning

strategy for the 3D primitive-variable resistive MHD formalism. It is based on “physics-based”

ideas [3, 4], in which knowledge of the physics is exploited to derive well-conditioned (diag-

onally dominant) approximations to the original system that are amenable to optimal solver

technologies (multigrid). The connection of the physics-based approach and the well-known

Schur decomposition will be stressed, and its generalization to include Hall effects discussed.

Grid convergence studies will demonstrate that CPU time scales scale optimally asO(N), where

N is the number of unknowns, and that the number of Krylov iterations scales asO(N0). If time

allows, we will discuss parallel performance using the PETSc toolkit.

References

[1] D. A. Knoll, L. Chacón, L. G. Margolin, and V. A. Mousseau, J. Comput. Phys.185, 583

(2003)

[2] L. Chacón, Comp. Phys. Comm.,163, 143 (2004)

[3] L. Chacón, D. A. Knoll, and J. M. Finn, J. Comput. Phys.,178, 15 (2002)

[4] L. Chacón and D. A. Knoll, J. Comput. Phys.,188, 573 (2003)


Particle in cell simulation of a Tonks-Langmuir model

T. Gyergyek1, N. Jelic2;3, M. Stanojevic3, S. Kuhn2, D. Tskhakaya jr.2;4, J. Duhovnik3

1 University of Ljubljana, Faculty of Electrical Engineering, Tržaška 25, SI-1000 Ljubljana,

Slovenia2 Department of Theoretical Physics, University of Innsbruck, Technikerstrasse 25, A-6020

Innsbruck3 University of Ljubljana, Faculty of Mechanical Engineering, LECAD Laboratory,

Aškeceva 6, SI-1000, Ljubljana, Slovenia4 Institute of Physics, Georgian Academy of Sciences, 380077Tbilisi, Georgia

Recently Kuhn et al [1] have presented an attempt to link fluidand kinetic parameters

near a negative electrode immersed in a plasma composed of electrons and singly charged

positive ions. They introduced the so-called Tonks-Langmuir velocity distribution for ions

and examined its behavior in the sheath and quasineutral plasma regions. Their results show

that for the fluid approach one should know the local properties of the velocity distribution at

any point in the plasma and based on it to find the local polytropic coefficientγi . In this work

we present the comparison of our computer simulations with the analytical results of Kuhn

et al. These simulations have been performed by means of the BIT1 code [2], developed on

the basis of the XPDP1 code [3] from the U.C. Berkeley. A plasma source, which produces

cold ions and maxwellian distributed electrons is localized in the middle of a plasma diode

bounded by two floating electrodes. The ion velocity distribution function is recorded in the

sheath and in the plasma at several positions between the source and the electrode. A good

agreement between theory and simulation is obtained. Some particular features apearead from

theoretical and simulation approach are analysed and discussed.

References

[1] S. Kuhn et al 31st EPS Conference on Plasma Physics, 28th June to 2nd July 2004,

Imperial College London, EPA, vol.28G, P5.122, (2004)

[2] D. Tskhakaya and S. Kuhn, Contrib. Plasma Phys.42, 302, (2002)

[3] J.P. Verboncoeur, M.V. Alves, V. Vahedi, and C.K. Birdsall, J. Comp. Physics,104, 321,

(1993)


Particle interactions with solitary waves in magnetized plasmas*

Y. Kominis and K. Hizanidis

School of Electrical and Computer Engineering, National Technical University of Athens, Association EURATOM-Hellenic Republic, Zographou GR-15773, Greece

In this work we investigate charged particle dynamics under interactions with Solitary Waves

(SW) propagating in a uniform magnetic field. The forms of the electric field range from

ordinary wave packets and solitons to ultrashort few-cycle and sub-cycle transient pulses.

Particle interactions with such waves is interesting for applications in RF plasma heating as

well as for the investigation of the damping of localized waves in plasmas, since the transit

time particle acceleration has been considered as the principal dissipation mechanism of

collapsing Langmuir solitons. Also, interactions with ultrashort pulses have several

applications to plasma physics. In order to study particle dynamics under interaction with a

SW with a continuous spectrum, the Canonical Perturbation Method (CPM) is utilized in

order to construct approximate invariants of the motion for the nonintegrable Hamiltonian

system describing particle motion. Most of the previous works in this field have considered

waves with discrete spectrum corresponding to localized periodic waves (pulse trains).

However, the aperiodic character of the Hamiltonian perturbation necessitates a modification

of the CPM in correspondence with recent extensions of the KAM theorem for aperiodic

perturbations. The resulting invariants contain essential information for the phase space of the

system, which is strongly inhomogeneous and is studied in terms of appropriate Poincare

surfaces of sections. For example, in the case of propagation along the field lines, the

structure of the phase space consists of: (a) strong interaction areas, where the particles are in

resonance with the SW, and the interaction results in momentum redistribution, and (b) weak

interaction areas where the particle motion is slightly modulated by the wave or is even

unaffected. The widths of the strong interaction areas are also analytically estimated, and the

resonance overlap is studied for the case of particle interaction with multiple waves at

different frequencies. Finally, the mean particle momentum variation, corresponding to

energy exchange with the SW is calculated. The analytical results are in good agreement with

results from direct numerical integration of the equations of motion.

* Work partially supported by and performed for the Association Euratom-Hellenic Republic, which is funded

by the Euratom Fusion Programme and the Secretariat for Research and Technology, Greece. The work is

also partially supported by the Grant “Pythagoras” of the Hellenic Ministry of Education. The contents of this

paper are the sole responsibility of the authors and do not necessarily represent the views of the European

Commission or its Services.


Non-linear excitation of magnetosonic waves through gravitational waves

in strongly magnetized plasmas

H. Isliker1, I. Sandberg

1, L. Vlahos

1

1 Section of Astrophysics, Astronomy and Mechanics, Department of Physics, University of Thessaloniki, GR 54006 Thessaloniki, GREECE

The interaction of a gravitational wave (GW) with a strongly magnetized plasma is studied

analytically and numerically. Our main interest is in the generation of magnetosonic waves

near resonance, where the relativistic Alfven speed approaches closely the speed of light.

The GW is considered a small disturbance, and the plasma is modeled by the induction

equation and the single fluid equations, including finite resistivity. The non-linear problem

is integrated numerically, and in parallel a linear analysis of the equations is performed. We

find that for strong magnetic fields the GW excites electromagnetic (EM) plasma

oscillations close to the magnetosonic modes, and large amounts of energy are absorbed by

the EM plasma oscillations from the GW. Moreover, the GW causes the generation of

harmonic oscillations, possibly of very high harmonic number. The resistivity plays a minor

role for the assumed plasma pameters.


Selecting, characterizing, and acting on drift waves and flute modes

turbulence in a low-β magnetized plasma column

F. Brochard, E. Gravier, G. Bonhomme

LPMIA, UMR 7040 CNRS-Université Henri Poincaré, BP 239, F-54506

Vandoeuvre-lès-Nancy Cedex, France

We report on experiments performed on the low-β plasma device MIRABELLE. Using a

limiter, we recently observed [1] that when increasing the magnetic field strength transitions

between various gradient driven instabilities occur. New thorough measurements allow to iden-

tify unambiguously three instability regimes. At low magnetic field the strongEr ×B veloc-

ity shear drives a Kelvin-Helmholtz instability, whereas at high magnetic field drift waves are

only observed. A centrifugal (Rayleigh-Taylor) instability is also observed in between when

the poloidal velocity field is shearless and strong enough. A close connection is made between

the ratioρs/L⊥ of the drift parameter to the radial density gradient length and each instability

regime.

The transition scenario from regular waves to turbulence was experimentally investigated. As

for drift waves the transition from regular state to spatio-temporal chaos and turbulence follows

the quasi-periodicity (or Ruelle-Takens-Newhouse) route.

Eventually we will present results on the efficiency of control and synchronization meth-

ods on Kelvin-Helmholtz and Rayleigh-Taylor spatio-temporal chaos in comparison with drift

waves.

References

[1] E. Gravier, F. Brochard, G. Bonhomme, T. Pierre, J.-L. Briançon, Physics of Plasmas11,

529 (2004)


Is the plasma at a plane probe unstable in the presence of fast electrons

producing secondary electrons?

S. Teodoru1,2, D. Tskhakaya1,3, S. Kuhn1 and G. Popa2 1Association Euratom-ÖAW, Department of Theoretical Physics,

University of Innsbruck, A-6020 Innsbruck, Austria 2Plasma Physics Department, Faculty of Physics, Al. I. Cuza University, RO-700506 Iaşi, Romania

3Permanent address: Institute of Physics, Georgian Academy of Sciences, 380077 Tbilisi, Georgia

In this work we intend to extend the double layer condition described by Hobbs and

Wesson [1] to a more complex plasma in which secondary electrons are released by a fast

electron beam. We take into account the reflected fast and thermal electrons and consider a

collisional plasma.

A dispersion relation is derived to analyse the three-stream instability produced by the

interaction of the fast incoming electrons with the fast reflected electrons and the secondary

electrons, embedded in the thermal-electron background.

For a better understanding of the problem, PIC simulations are performed for a plane

probe immersed in an unmagnetised plasma where charged-neutral collisions, as well as

fast and secondary electrons are included in the model. We use the 1d3v (one spatial and

three velocity dimensions) code BIT1 [2] developed on the basis of the XPDP1 code [3].

The behaviour of the simulated Volt–Ampère characteristic is different from the one

predicted by linear analytical models [4]. Our explanation is based on the influence of

instabilities, which lead to the formation of trapped-particle structures.

[1] Hobbs and G. D. Wesson, “Heat flow through a Langmuir sheath in the presence of electron emission”, Plasma Phys. 9, 85, Pergamon Press (1967).

[2] D. Tskhakaya and S. Kuhn, “Effect of E×B drift on the plasma flow at the magnetic presheath entrance”, Contrib. Plasma Phys. 42, 302 (2002).

[3] J. P. Verboncoeur, M. V. Alves, V. Vahedi, and C. K. Birdsall, Simultaneous potential and circuit solution for 1D bounded plasma particle simulation codes, J. Comput. Phys. 104 (2), 321 (1993).

[4] S. Teodoru, D. Tskhakaya jr., S. Kuhn, R. Schrittwieser, D. Tskhakaya sr., and G. Popa, Theory of a plane probe in a collisional plasma with fast electrons producing secondary electrons at the probe surface, 31st EPS Conference on Plasma Physics, London, U. K., 28 June – 2 July 2004, Contributed Papers CD, ECA 28G, P-5.123 (2004).


Consistency of the Accretion Theory of the Spontaneous Rotation Phenomenon with Recent Experiments*

M. Lontano1, B.Coppi2 1CNR, Milan, Italy

2MIT, Cambridge, USA

The accretion theory [1] of the spontaneous rotation phenomenon has found further

confirmation in the series of experiments carried out by the Alcator C-Mod [2] and DIII-D

machines [3]. This theory has been the first to be based on having the source of angular

momentum near the edge of the plasma column implying that a change of the edge

configuration can affect the velocity of rotation. This feature is consistent with the Alcator C-

Mod experiments producing lower and upper null poloidal field configurations that have found

drastically different toroidal velocities. The intrinsic coupling between spontaneous rotation and

thermal energy transport involved in the accretion theory is consistent with the observed

relationship [2] between the change of rotation velocity from the L-confinement regime to the

H-confinement regime and the scaling of the threshold to attain the H-regime. The DIII-D

experiments with electron cyclotron heating have confirmed the existence of spontaneous

rotation and shown the toroidal velocity to be proportional to (Te/Ti)Wth where Wth is the total

thermal energy of the plasma column and the (Te/Ti) is the electron to ion temperature ratio.

This is consistent with the characteristics of the ion temperature gradient driven (ITG) modes

whose excitation is involved within the accretion theory in order to carry angular momentum

from the edge toward the center of the plasma column [1].

Recent relevant advances for the accretion theory are reported in this context.

*Sponsored in part by the US DOE and by the CNR of Italy [1] B. Coppi, Nucl. Fusion 42, 1 (2002 ) [2] J. Rice et al, Paper IAEA-CN-116/EX/6-4Ra, I.A.E.A. Fusion Conference 2004 (Publ.

I.A.E.A., Vienna, 2004) [3] J. S. deGrassie et al, Paper IAEA-CN-116/EX/6-4Rb, I.A.E.A. Fusion Conference 2004

(Publ. I.A.E.A., Vienna, 2004)


Beam Tracing solution of the (weakly nonlinear) Burgers’ equation

O. Maj1, G. V. Pereverzev2

1 Physics Department “A. Volta”, University of Pavia, I-27100 Pavia, Italy2 Max-Planck-Institut für Plasmaphysik, EURATOM Association,

D-85748 Garching, Germany

The beam tracing method [1-3] is an asymptotic technique for solvinglinear wave equa-

tions, with reference, in particular, to the propagation of electrostatic [1] as well as to elec-

tromagnetic waves in both isotropic and anisotropic (spatiallly nondispersive) plasmas [1, 2],

and, more recently, it has been succesfully applied also to the description of short wavelength

eigenmodes in a tokamak (microinstabilities) [3]. However, the beam tracing treatment of mi-

croinstabilities in the linear regime should be improved in order to account for nonlinear effects

which are significant when the amplitude of an unstable eigenmode grows up. With this aim,

the beam tracing solution of (weakly)nonlinearwave equations is needed.

In this work, as a first step toward a beam tracing treatment of generic (weakly) nonlinear

wave equations, the beam tracing solution of the Burgers’ equation [4], with weakly nonlinear

effects, is addressed. Specifically, such an equation describes the propagation in one spatial

dimension (plus time) of a wavepacket with a propagation speed proportional to the amplitude

of the wave itself, the beam tracing solution of the corresponding linear problem (for which

the propagation speed does not depend on the wave amplitude) being obtained on the basis of

the paraxial complex eikonal method [5], which constitutes a straightforward generalization of

the beam tracing approach. A detailed comparative analysis between the linear and nonlinear

solution is also given.

References

[1] G. V. Pereverzev, Reviews of Plasma Physics19, 1-51 (1996)

[2] G. V. Pereverzev, Physics of Plasmas5, 3529 (1998)

[3] G. V. Pereverzev, Physics of Plasmas8, 3664 (2001)

[4] L. Hörmander, Lectures on Nonlinear Hyperbolic Differential Equations, Springer

(1997)

[5] O. Maj and M. Bornatici, Proc. 30th EPS Conf. on Controlled Fusion and Plasma Physics,

ECA 27A (2003)


A ionization instability in weakly ionized unmagnetized plasmas with

negatively charged dust grains

L. Conde, C. Ferro Fontán and N. Franco

Dpto. Física Aplicada, E.T.S.I Aeronáuticos

Universidad Politécnica de Madrid

28040 Madrid, Spain

The injection of a suprathermal electron current densityJeb in weakly ionized plasmas

with energy exceeding the ionization energy of the neutral gas may trigger a ionization in-

stability [1]. The consideration of additional negativelycharged dust grains in this plasma

is investigated in present work with emphasis the influence ofdust chargeZ. In this linear

model a more involved four degree polynomial dispersion relation is deduced making use

of a linearized Poisson equation instead of the currently used quasineutral approximation.

The consideration of appropiate time and lenght scales leadto a dimensionless wave number

κ λiaK and growth rateω Ωνia whereνia is the frequency for elastic collisions beween

ions and neutral atoms andλia the corresponding mean free path.

Contrary to dust free plasmas the ionization instability could

be triggered even forJeb 0. The two unstable roots (Im ω

ωI κ 0) of the dispersion equation present an exponential aperi-

odic (Re ω ωR κ 0) growth rates which are compared in the

figure with those obtained by using the quasineutral approximation.

Two ustable positive and two stable negative branchs start at κ 0

which later join in single curve after a bifurcation point. This unsta-

ble root later decreases down to a maximum unstable wave number

related with the minimum allowed length for space charge fluctuations. The dust chargeZ

increments the instability growth rates and brings the bifurcation point to larger values ofκ .

A similar response is observed increasingJeb for constant dust grain charge.

References

[1] L. Conde,Phys. Plasmas, 11, (5), pp. 1955-1959, (2004).


Revelation of the Sun Self-Similarity Skeletal Structures

V. A.Rantsev-Kartinov

INF RRC "Kurchatov Institute", Moscow, Russia, [email protected]

The analysis of a database of photographic images of the Sun, its atmosphere and the nearest

space environment (received in various conditions of its activity, and taken at various magni-

fications and spectral ranges) has revealed the presence of the Sun skeletal structures (SSS)

as on itself the Sun such in its surrounding, both on its surface, and in chromospheres and its

space environment. The SSS show the tendency to self-similarity on various scales. The SSS

topology appears to be identical to those which have been formerly found out in a wide

range of length scales (as much as about 30 orders of magnitude), media and for various

phenomena in laboratory, Earth atmosphere and space. [1, 2]. The SSS analysis has revealed

block character of their structure. The SSS long filaments will consist of direct almost iden-

tical coaxial-tubular (C!) blocks with internal radial bonds flexibly jointed with each other,

as in a skeleton. It is assumed such joints may be realized due to stringing of the individual

CT blocks on common the magnetic field flow which penetrates the whole of such filament,

and itself the CT blocks are interacting magnetic dipoles with skeletons, which immersed

into plasma. In the SSS such as a “cartwheel-like” structures, as the edges of the CT blocks,

or as independent blocks on own axes are observed also. The SSS show properties, as earlier

described structures [1c, d]. In this paper they are demonstrated the revealed structures, as

dark spots, globular structures of photosphere, protuberances, structures of the Sun atmos-

phere and powerful solar coronal mass ejection. Diameters the revealed CT structures lay in

limits (108 - 2.5 1012) cm. At time observing of such structures the SSS blocks speeds ~ (107-

108) cm/s are estimated.

REFERENCES

[1] A.B.Kukushkin, V.A.Rantsev-Kartinov, a) Laser and Particle Beams, 16, 445,(1998); b)

Rev.Sci.Instrum., 70, 1387,( 1999); c) Proc. 17-th IAEA Fusion Energy Conference, Yoko-

hama, Japan, 3, 1131, (1998); d) Proc. 26-th EPS PPCF, Maastricht, Netherlands, 873,

(1999); e) Phys.Lett. A, 306, 175; f) “Advances in Plasma Phys. Research”, (Ed. F. Gerard,

Nova Science Publishers, New York), 2, 1, (2002).

[2] B.N.Kolbasov, A.B.Kukushkin, V.A.Rantsev-Kartinov, et.set., Phys. Lett. A:a) 269,

363, (2000); b) 291, 447, (2001); c) Plasma Devices and Operations, 8 , 257, (2001).


mailto:[email protected]

On periodic change of differential rotation and global magneto-fluid

structure of the sun

S. -I. Itoh1, K. Itoh2, A. Yoshizawa3, P. H. Diamond4, N. Yokoi5

1 Research Institute for Applied Mechanics, Kyushu University 87, Kasuga 816-8580, Japan

2 National Institute for Fusion Science, Toki 509-5292, Japan

3 3-2-10-306, Tutihasi, Miyamae-ku, Kawasaki 216-0005, Japan

4 Department of Physics, University of California San Diego, San Diego CA 92093-0319,

U.S.A

5 Institute of Industrial Science, University of Tokyo, Komaba, Tokyo 153-8505, Japan

The periodic oscillation of the inhomogeneous rotation of the sun and possible global

solar magneto-fluid structure are studied by use of mean field MHD dynamo theory. There

exists a turbulent electromotive force which is driven by the vorticity of the flow (i.e., the

!-dynamo [1]). In addition, its counterpart exists in the vorticity equation, that is, rotation is

induced by inhomogeneous Lorenz force in turbulent plasmas, as well. Based on this

dynamo theory, a periodic change of solar differential rotation with the period of 11 yr is

explained theoretically for the prescribed solar magnetic cycle. The predicted amplitude is

compared with observations [2]. We also compare the prediction of the !-dynamo model

with a model of torsional oscillations based on ∀ quenching by turbulence induced

magnetic stress.

The dynamo theory is also applied to obtain a possible solution of global magneto-fluid

structure of the convection zone. An example is obtained by use of spherical-Bessel (in

radius) and associated Legendre (in poloidal) functions.

Since the !-dynamo works in proportion to both the turbulence cross helicity and the mean

potential vorticity, we are exploring the effect of large scale vorticity on a unidirectional

Alfven wave spectrum to understand resulting changes in the mean turbulence driven EMF.

Results of these analyses will be reported.

References:

[1] A. Yoshizawa, S.-I. Itoh, K. Itoh, N. Yokoi; Plasma Phys. Contr. Fusion 46 (2004) R25

[2] S. -I. Itoh, et al.: Astro Phys. J. 618 (2005) 1044


Bright XUV harmonic generation in the water window.

B. Dromey

Queens University Belfast [email protected]

The efficient generation of coherent XUV radiation on the Vulcan Petawatt laser is reported.

The observed spectrum extends past the 'water window' region of the spectrum, which is of

particular relevance to biological imaging applications. The XUV light is produced via ultra-

high harmonic generation from laser/solid target interactions, as reported by Gibbon1 and

Norreys2. Harmonics of an Nd:Glass laser have been observed in the water window with

conversion efficiencies >10-6

in the spectral region below 17nm. This method of harmonic

generation should also be applicable to ultra-high power, high repetion rate Ti:Sapphire lasers

currently being constructed.

[1] Gibbon, P., Harmonic Generation by Femtosecond Laser-Solid Interaction: A Coherent “Water -Window”

Light Source?, Phys. Rev. Lett. 76, 50 (1996).

[2] Norreys, P. A., et al., Efficient Extreme UV Harmonics Generated from Picosecond Laser Pulse Interactions

with Solid Targets., Phys. Rev. Lett. 76, 1832 (1996).


Microwave Emission from Magnetized Wake of Laser Irradiated Gas Jet

D. Dorranian1, M. Ghranneviss1, A. H. Sari1, M. Starodubtsev2, N. Yugami3, Y. Nishida3

1 Plasma Physics Research Center, Science and Research Campus, I. Azad University,

Tehran 14778, Iran2 Institute of Applied Physics RAS, 46 Ulyanov St., Nizhny Novgorod 603950, Russia3 Graduate School of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya,

Tochigi 321-8585 Japan

Plasma wakefield due to the interaction of laser and the flow of a gas jet is basically elec-

trostatic and the dimension of the interaction region does not allow us to use a physical prob

for measuring the wake parameters. In this work by applying an external dc magnetic field, the

electromagnetic component of the plasma wakefield is formed and observed in the vacuum.

Wakefield is excited by a mode locked Ti:sapphire laser beam operating at 800 nm wave-

length with the pulse width of 100 fs (FWHM) and maximum energy of 100 mJ per pulse with

10 Hz repetition rate. The neutral density of gas-jet flow is measured with a Mach-Zehnder in-

terferometer. Strength of the applied external dc magnetic field normal to the direction of laser

pulse propagation varies from 0 to 8 kG in the interaction region. Radiation is observed, in the

forward direction due to the axial component of the magnetized wakefield and in the normal

direction due to the radial component of the magnetized wakefield, both perpendicular to the

direction of the applied magnetic field. The frequency of the emitted radiation with the pulse

width of 200 ps (detection limit), measured by the method of time-of-flight, is in the millimeter

wave range. Radiations are polarized perpendicularly to the laser pulse propagation direction

and dc magnetic field lines as is expected from the theory. Electrodynamic properties of the

radiation have been studied at different plasma densities and magnetic field strengths. Results

clearly show the resonant behavior of the wakefield intensity versus plasma density and different

regime of wakefield due to laser spot size.


High density ECR plasmas for the production of intense highly charged

ion beams

S. Gammino1, G. Ciavola1, L. Celona1, L. Torrisi1, S. Passarello1, L. Andò1, M. Presti1,

F. Consoli1 , P. Spädtke2, K. Tinschert2, M. Winkler2, D. Hitz3, A. Girard3

1INFN-LNS, Catania, Italy

2GSI Darmstadt, Germany

3CEA-DRFMC-SBT, Grenoble, France

An average increase of about one order of magnitude per decade in the performance of ECR

ion sources was obtained up to now since the time of pioneering experiment of R. Geller at

CEA Grenoble and this trend is not deemed to get the saturation at least in the next decade,

according to the increased availability of powerful magnets and microwave generators.

Otherwise a further step forward is needed to fulfil the requirements of many projects of

accelerators recently proposed or in the construction phase. For this reason a relevant

research effort was done within the 5th Framework Programme with the aim to test the

powerful ECRIS source of INFN-LNS, Catania, at higher operating frequency (28 GHz); the

results permitted to compare the source performance with a high confining B-minimum field

(the so called High B mode) at 18 GHz to the one at 28 GHz with a higher plasma density

but with a worse confinement time (the most relevant parameter for the ECRIS plasma

confinement is the ratio between Bmax and BECR). The results of this experiment confirmed

the validity of the so-called ‘Standard Model’ for the ECRIS plasma, but opened a new

question concerning the ability to extract and transport intense beams produced by high

density plasmas. The solution of this problem will be described along with the details of the

experiments already done and with the major issues of experiments in preparation for 2005-

06 with the SERSE source at INFN-LNS.

Electron density above 1013 cm-3 can be obtained by 28 GHz microwave heating, but only an

adequate plasma trap may allow to exploit that plasma for heavy elements ionization. The

rule of thumb that will permit to get in future from the same ECR ion source either mA

beams of 20+ to 30+ heavy ions or µA beams of 50+ to 60+ ions, through the change of a few

parameters, within a short time (minutes or hours), will be proposed.


Generation of monoenergetic electron beams

in a plasma-wave potential dr iven by an intense laser pulse

M.Tanimoto1, K.Koyama

2, E.Miura

2, S.Kato

2 and M.Adachi

3

1. Department of Electrical Engineering, Meisei University, 2-1-1, Hodokubo, Hino, Tokyo,

191-8506, Japan

2. National Institute of Advanced Industrial Science and Technology, Tsukuba Central 2,

1-1-1, Umezono, Tsukuba, Ibaraki, 305-8568, Japan

3. Hiroshima University, 1-3-1, Kagamiyama, Higashi Hiroshima, Hiroshima, 739-8530,

Japan

In recent laser-driven plasma acceleration experiments have demonstrated production of

energetic electron beams with a moderate energy spread [1], stimulating further

improvement of a quality of electron beams.

In the experiments carried out at National Institute of Advanced Industrial Science and

Technology (AIST) [2-4], collimated quasi-monoenergetic electron beams are generated

from plasmas driven in supersonic gas jets by irradiating 2TW/50fs Ti: sapphire laser

pulses (700nm). A typical peak energy, energy spread and angular divergence are 7MeV,

20% and 2.4deg, respectively. These monoenergetic beams are observed only within a

relatively narrow window of the experimental conditions (especially an electron density).

The observed transition of the electron energy from a Boltzmann-like to a peaked

distribution show strong correlation with excitation of the laser driven plasma wave

monitored forward scattered light spectra.

Based on a simple 1D model, the electron acceleration in wake potentials is studied to

identify dominant factors contributing to the improvement in a beam quality in the existing

acceleration experiments. Following trajectories of the driven electrons in a phase space,

energy distributions of ejected electrons due to dephasing are compared with the

experimental observation.

[1] C.G.R.Geddes et al., Nature, 431, (2004) 538.

[2] M.Adachi et al., 31st EPS Plasma Physics Conf. P5-024 (2004, London).

[3] K.Koyama et al., 11th

Advanced Accelerator Concepts Workshop (Stony Brook, 2004)

[4] M.Adachi et al., PSS 2005/SPP (2005, Nagoya) P2-114.


Optimization of proton beams created by laser-plasma

interaction for various applications

E. d’Humières1, E. Lefebvre1, L. Gremillet1, V. Malka 2

1 Commissariat à l’Energie Atomique, DIF, Bruyères-le-Châtel, France

2 LOA, ENSTA-Ecole Polytechnique, Palaiseau, France

A high intensity laser pulse interacting with a plasma can create energetic and

well-collimated proton beams. The whole accelerating system (laser and target

chamber) is very compact when compared with synchrotrons or linacs. Therefore,

these proton beams are very promising for applications in inertial confinement fusion,

plasma diagnostics, isochoric heating of matter or medical applications.

When a high intensity laser hits a very thin overdense target, the target is

quickly heated and expands. The density of the plasma decreases and induced

transparency becomes possible. Part of the laser pulse is transmitted and the bulk of

the target is efficiently heated. Proton acceleration is optimized in this regime but the

divergence of the beam is affected. It is possible to find a thickness between the

opaque regime, when the laser is reflected by the target, and this transparency regime

for which the divergence of the beam is not too affected and the maximum proton

energy is much higher than in the classical opaque regime. The optimum thickness is

very sensitive to target density, pulse duration and laser intensity.

For very high intensities (1020-1021 W/cm2), shock acceleration from the front

or the core of the target is increased and the most energetic protons can first be

accelerated by this mechanism. In this case, the number of protons accelerated to the

highest energies is smaller than when the most energetic protons are accelerated from

the back surface. These shock-accelerated beams are therefore less interesting for

most applications than proton beams coming directly from the back of the target.

Proton acceleration with an underdense target is similar to the transparency

regime and also presents an optimum thickness. Coupling an underdense plasma with

an overdense plasma can be a benefit for some applications and has been investigated.

We will review different applications of laser-based proton acceleration and for each

one of them, look at the most interesting parameters.


Laser wakefield acceleration of electron bunches in the mildly nonlinear

regime

A. Lifschitz1, V. Malka1, J. Faure1 and P. Mora2

1 Laboratoire d’Optique Apliquée, Ecole Polytechnique, ENSTA (UMR 7639 du CNRS),

91761 Palaiseau, France2 Laboratoire de Physique Théorique, Ecole Polytechnique (UMR 7644 du CNRS), 91128

Palaiseau, France

Experimental and theoretical efforts performed during last years have shown the feasibility

of laser-plasma electron accelerators. Laser wakefield acceleration has allowed to produce

high quality electron beams of energies up to≈ 170 MeV [1]. Next generation of Petawatt

lasers would allow to reach the GeV range. Numerical studiespredict that such energies can

be attained in a single stage device working in the strongly nonlinear regime (a0 ≫ 1, with

a0 the normalized laser amplitude) [2]. To enhance the flexibility and the control capability

over the beam properties, a two-stage scheme in the mildly nonlinear regime (a0 ≈ 1− 2)

is envisaged [3]. In this work, we present analytical and numerical results on the wakefield

acceleration of electron bunches of some MeVs to GeVs energies using wide unchanneled laser

pulses. Analytical expressions derived in the linear response framework are able to predict the

main features found in the nonlinear numerical calculations in this mildly nonlinear regime.

In particular, the enhancement in the beam quality when the initial electron energy is close to

the minimum for trapping can be explained, along with the effect over the energy spread of

the relativistic shift of the plasma frequency. Derived scaling laws for the beam energy, the

energy spread and the beam length are in good agreement with numerical results and allow us

to optimize plasma and injection parameters.

References

[1] J. Faureet al, Nature431, 541 (2004)

[2] A. Pukhovet al, Plasma Phys. Control. Fusion46, B179 (2004)

[3] L. M. Gorbunov, S. Yu. Kalmykov and P. Mora, Phys. Plasmas12, 033101 (2005)


Detailed studies of the transverse beam character istics of laser produced

ion beams

Erik Brambrink1,2

, P. Audebert2, A. Blazevic

1, R. Clarc

3, J. Cobble

4, T.E. Cowan

5, J.

Fernandez4, J. Fuchs

5, M. Geißel

1, M. Hegelich

4, S.Karsch

3, P. McKenna

6, K. Ledingham

6,

H. Ruhl5, T. Schlegel

1, J. Schreiber

7 and M. Roth

1

1. Darmstadt University of Technology, Germany

2. LULI, Ecole Polytechnique, Paliseau, France

3. RAL, Didcot, Great Britain

4. Los Alamos National Laboratory, USA

5. University of Nevada, Reno, USA

6. University of Strathclyde, Great Britain

7. MPQ, Garching, Germany

The generation of laser produced proton and ion beams is still under heavy investigation.

Especially the acceleration of protons from the rear side of the target by an electrostatic

field is due to their unique beam properties and various possible applications a topic of

research activities.

Experiments with structured targets are a powerful tool to diagnose the properties of the

electron sheath, the acceleration mechanism at very early times and proton beam

parameters like source size and emittance.

Experiments over a wide range of laser parameters show, that beam properties like source

size and divergence of the proton beam show a similar behavior over a wide range of laser

intensity and energy. The dependence of the source size on the target thickness implies an

electron transport through the target, which is not influenced by magnetic or electric fields.

We will also introduce an analytic model to describe the properties of the electron sheath

and their influence to the spatial ion beam distribution. This model was supported by

detailed simulations.


Detailed study of the photon accelerator

F. Fiúza, J. M. Dias, S. F. Martins, R.A. Fonseca, L.O. Silva

GoLP/Centro de Física dos Plasmas, Instituto Superior Técnico, Lisboa, Portugal

The wake driven by a short intense laser pulse propagating in a transparent plasma can be

used to accelerate charged particles (the laser wakefield accelerator) [1], and to up-shift or

downshift another ultrashort electromagnetic pulse co-propagating with the wake (the photon

accelerator) [2]. For large amplitude plasma waves, photon acceleration/deceleration is a

powerful diagnostic for the structure of the wake, and it provides a mechanism to tune the

frequency of short laser pulses.

We have performed detailed fully relativistic one-dimensional, two-dimensional, and three-

dimensional particle-in-cell simulations with osiris 2.0 [3] of the photon accelerator, over a

wide range of realistic laboratory conditions for the neutral gas background, the plasma

background, the wake field driver, and the probe. Our study relies on the systematic use of

the Wigner transform for the electromagnetic field, thus allowing for a complete diagnostic

of the frequency modulations in the probe pulse. Our results are compared with ray-tracing

simulations [4]. We demonstrate controlled tunability of the probe pulse, and the injection

conditions for maximum up-shift/downshift are determined.

[1] T. Tajima and J. M. Dawson, Phys. Rev. Lett. 43, 267 (1979).

[2] S. C. Wilks et al., Phys. Rev. Lett. 62, 2600 (1989).

[3] R.A. Fonseca et al., Lect. Notes Comp. Sci. 2329, III-342 (Springer-Verlag, Heidelberg,

2002).

[4] J. M. Dias et al., Phys. Rev. E 65, 036404 (2002).


Explosion Dynamics of Heterogeneous Nanoplasmas

J.L. Martins1, F. Peano2, M. Fajardo1, R.A. Fonseca1, L.O. Silva1

1 GoLP/Centro de Física dos Plasmas, Instituto Superior Técnico, Lisboa, Portugal

2 Dipartimento di Energetica, Politecnico di Torino, Italy

Ultra-intense laser pulses interacting with clustered media can drive strong Coulomb

explosions [1]. The laser field extracts all the electrons from each cluster, and the remaining

ion spheres explode due to the electrostatic repulsion between the ions. Recently, we have

demonstrated the possibility to control these explosions by driving large-scale shock shells

(cf. [2]) inside very large clusters [3], and to enhance intracluster nuclear fusion reaction rates

in very large deuterium clusters [4].

We have further explored the possibility for detailed control of the Coulomb explosions by

considering the explosion of clusters with heterogeneous compositions, either by assuming

layered targets or very large clusters/liquid droplets with different compositions (species with

different charge to mass ratios/ionization states). These scenarios were explored with multi-

dimensional particle-in-cell simulations with OSIRIS 2.0 [5], in the nanoplasma

approximation. Our results show that even for heterogeneous clusters, the dynamics of the

explosion can be controlled. The presence of different ionization states and charge to mass

ratios increases the complexity of the phenomena, leading to explosions occurring on

different time scales for the different ion species. This in turn leads to modulations in the

time-dependent spectrum of the ions accelerated in the Coulomb explosions.

[1] T. Ditmire et al., Nature 386, 54 (1997); T. Ditmire et al., Nature 398, 489 (1999).

[2] A.E. Kaplan, B.Y. Dubetsky and P.L. Shkolnikov, Phys. Rev. Lett. 91, 143401 (2003).

[3] F. Peano, R.A. Fonseca and L.O. Silva, Phys. Rev. Lett. 94, 033401 (2005).

[4] F. Peano et al., Phys. Rev. A, submitted (2005).

[5] R.A. Fonseca et al., Lect. Notes Comp. Sci. 2329, III-342 (Springer-Verlag, Heidelberg,

2002).


Optimizing wave breaking and self injection in the laser wake field

accelerator

J. F. Vieira1, R. A. Fonseca1, L. O. Silva1, F. Tsung2, W. B. Mori2

1 GoLP/CFP, Instituto Superior Técnico, Lisboa, Portugal2 University of California Los Angeles, CA 90095, U.S.A.

Recent experimental results showed that electron acceleration via laser wake field is an ef-

fective way to accelerate electrons to the hundred ofMeV range in high quality beams [1]. The

results indicate that this novel regime requires laser intensities above a certain threshold. Nu-

merical experiments also show that, with present day laser technology, it is feasible to accelerate

electrons to theGeV range, in the same regime, by making use of a parabolic plasma channel

to guide the laser [2].

The physics is very complicate, and it is now necessary to determine the optimal parameters

that lead to self injection and controlled wave breaking. We have carried out a systematic study

of how does self injection occur, by performing three dimensional PIC simulations in osiris

2.0 [3], in the limit of high laser intensities,a0 > 1, and wide shot,kpw0 > 1. This set of 3D

simulations allowed us to test the predictions of a theoretical model for self injection in laser

wake field in a channel. The theoretical model considers three major physical mechanisms: (i)

the formation of the blow-out region; (ii) the transverse wave breaking of the plasma wave and

(iii) the self injection of the electrons when the longitudinal velocity of the electrons, in the

wave breaking region, is comparable with the phase velocity of the plasma wave.

We show that to optimize self injection, the laser pulse length should be half the relativis-

tic period of oscillation and the laser spot size should be small, in order to increase the radial

ponderomotive force. Our model also shows that the channel does not enhance wave break-

ing or self injection, being only critical to guarantee guiding of the laser pulse over distances

comparable to the pump depletion length.

References

[1] C.G.R. Geddes et al, J.Faure et al, S.P.D.Mangles et al, Nature431, 30 September 2004

[2] F. Tsung et al, Phys. Rev. Lett.93, 185002 (2004); R.A. Fonseca, I.S.T. PhD Thesis (2003);

R.A. Fonseca et al, submitted Phys. Plasmas (2004)

[3] R. A. Fonseca et al., LNCS 2331, 342-351, (Springer, Heidelberg, 2002).

[4] J.M. Dawson Phys. Rev.113, 383 (1959)


Controllable generation of a single attosecond relativistic electron bunch

by a superintense laser pulse with a sharp rising edge

Victor V. Kulagin 1, Vladimir A. Cherepenin2, Min Sup Hur1, Hyyong Suk1

1 Center for Advanced Accelerators, KERI, Changwon, Republic of Korea 2 Institute of Radioengineering and Electronics RAS, Moscow, Russia

Energetic ultrashort electron bunches can be used in many fields of science and

technology. For controllable generation of ultrashort electron beams, we propose to use a

thin plasma layer (either with compensating positive charge or without it) irradiated

normally by a super-high intensity laser pulse with a sharp rising edge [1-3]. The electrons

of the plasma layer are accelerated during laser pulse action longitudinally to relativistic

velocities by the nonlinear component of the Lorentz force, provided a dimensionless field

amplitude is large enough, a0>>1. We show analytically and by two-dimensional PIC

simulations that it is possible to choose the parameters of the laser pulse and the plasma

layer in such a way that only a single short and ultracold relativistic electron beam will be

produced (and can survive for some time) rather than a cloud of chaotically moving

electrons. First, the transparency of the plasma layer has to be large enough for the

electrons to interact with a propagating laser pulse rather than a standing wave. Then, the

amplitude of the laser pulse has to be large enough. And at last, the laser pulse has to be

nonadiabatic, i.e., with a very sharp rising edge and duration about four to five periods of

the laser frequency. These ensure that the bunch will be compressed by many times in the

longitudinal direction at the initial stage of interaction with the front of the laser pulse,

giving the resulting bunch duration on the attosecond scale and smaller. As a possible

application, frequency up-conversion of the probe laser pulse into a single, ultrashort

(attosecond), and coherent hard X-ray pulse due to backscattering off such an electron

bunch is demonstrated numerically and the spectrum of up-shifted radiation is investigated.

Here, the electron and the X-ray beams are generated synchronously by the laser pulse,

which provides a unique opportunity for use.

References

[1]. V. V. Kulagin, V. A. Cherepenin and H. Suk, Phys. Lett. A, 321, 103 (2004).

[2]. V. V. Kulagin, V. A. Cherepenin and H. Suk, Appl. Phys. Lett., 85, 3322 (2004).

[3]. V. V. Kulagin, V. A. Cherepenin and H. Suk, Phys. Plasmas, 11, 5239 (2004).


Generation of relativistic high-energy electrons by laser wakefield

acceleration at KERI

H. Suk1, I.W. Choi2, N. Hafz1, C. Kim1, G.H. Kim1, D.K. Ko2, J. Lee2, T.J. Yu2

1 Center for Advanced Accelerators, KERI, Changwon, Republic of Korea 2 Advanced Photonics Research Institute, GIST, Republic of Korea

Laser wakefields can provide much stronger electric fields for charged particle

acceleration compared to RF-based conventional accelerators. We used a 2 TW (1.4 J/700

fs) Ti:sapphire/Nd:glass laser system at KERI (Korea Electrotechnology Research Institute)

to generate MeV-level high-energy electrons by the self-modulated laser wakefield

acceleration, in which a plasma density of 190 10=n cm-3 was used. The generated electron

beam pulse had a large charge with more than 1 nC and the energy was up to 5 MeV. By

using a small collimator with a hole size of 1 mm we could produce an electron beam with a

rather narrow energy-spread, where most low energy electrons with a higher space-charge

effect can not pass through the small hole. More detailed experimental and simulation results

are presented. In addition, we have an ongoing laser wakefield acceleration experiment in

collaboration with GIST (Gwangju Institute of Science and Technology), where a 20 TW

Ti:sapphire laser is available now. The recent experimental results will be presented as well.


Physics of the formation of collisionless shocks

M. Marti1, G. Sorasio1, R.A. Fonseca1, L.O. Silva1, W.B. Mori2

1 GoLP/Centro de Física dos Plasmas, Instituto Superior Técnico, Lisboa, Portugal

2 Dep. Physics and Astronomy, University of California Los Angeles, California 90095

We have recently shown that electrostatic collisionless shocks, previously observed in

numerical experiments with a piston [1], can be driven by ultra intense laser pulses [2].

In this work, we explore the physics of collisionless shocks by comparing the results of the

numerical simulations carried out with osiris 2.0 [3] with our theoretical predictions. The

present analysis explores the two aforementioned driving mechanisms (i.e. piston vs. laser)

by highlighting the similarities and examining critical parameters such as jump conditions,

electron temperature, electron trapping, and shock velocity. The influence of the plasma

parameters on the maximal shock velocity is explored in detail, and the results are

theoretically investigated.

The laser/piston - induced shocks are also probed in the absence of a preformed plasma by

running the laser on a non-ionized target. The effects of collisions on the shock structure

and properties are investigated. Shock front control and shock guiding is explored through

shaping of the density/temperature distribution in the targets.

Work partially supported by FCT (Portugal) and DoE.

[1] D. W. Forslund, and C.R. Shonk, Phys. Rev. Lett. 25, 1699 (1970).

[2] Luís O. Silva, Michael Marti, Jonathan R. Davies, et al, Phys. Rev. Lett. 92, 015002

(2004); Michael Marti et al, submitted to Phys Rev. E (2005).

[3] R. A. Fonseca et al, LNCS 2331, 342 (Springer, Heidelberg, 2002).


New setups to improve proton acceleration with high intensity lasers

E. d’Humières1, E. Lefebvre1, L. Gremillet1, D. Patin1, A. Bourdier1,

V. Malka 2, T. Fuchs3

1 Commissariat à l’Energie Atomique, DIF, Bruyères-le-Châtel, France

2 LOA, ENSTA-Ecole Polytechnique, Palaiseau, France

3DKFZ, Heidelberg, Germany

A high intensity laser pulse interacting with a plasma can create energetic and

well-collimated proton beams. The whole accelerating system (laser and target

chamber) is very compact when compared with synchrotrons or linacs. Therefore,

these proton beams are very promising for applications related to inertial confinement

fusion, plasma diagnostics, isochoric heating of matter or medical applications.

The possibility of producing a low emittance energetic proton beam by means

of a high intensity laser interacting with a solid target has been demonstrated

experimentally and extensively investigated theoretically over the past years. There is

now an increasing need to work out new setups capable of improving the proton beam

properties.

Configurations coupling two targets, two lasers, or both, look particularly

encouraging in this respect. The electrostatic field that arises at the back of a target

irradiated by a high intensity laser can be used to boost protons accelerated from

another irradiated target. This multi-stage scheme proves to be very sensitive to target

and laser parameters. We have performed 2D PIC simulations to study this process

and determine favorable parameters.

Using only one target but two or three laser beams can lead to an increase in

electron heating and therefore to a better proton acceleration. This configuration

involves complex intertwined phenomena, which 2D PIC simulations may help to

discriminate. We have also investigated the influence of a preformed preplasma on

the different setups proposed to enhance proton acceleration.


Design and characterization of gas jets for laser-plasma interaction

F. Viola, N. Lemos, N. C. Lopes, G. Figueira, J. M. Dias

GoLP/Centro de Física dos Plasmas, Instituto Superior Técnico, Lisboa, Portugal

Experiments on high intensity laser-gas interaction require the use sharp edge and well de-

fined pulsed gas jets in to order avoid ionization induced refraction and achieve the maximum

intensity on the focal spot. Supersonic Laval nozzles can produce sharp gas jets in vacuum

with uniform gas density and are suitable for applications such as the production of relativistic

ionization fronts, laser wakefield acceleration, harmonic generation or x-ray laser schemes [1].

In this work, we report the design and test of Laval supersonic nozzles for high intensity

laser-plasma interactions in the L2I 10 TW laser facility. The nozzle shape was designed using

the method of the characteristics [2] and the density profiles of the gas jets were determined

by time-resolved Mach-Zehnder interferometry. The interferogram analysis was preformed by

a developed automatic fringe-pattern analysis code [3]. The density of the plasmas produced by

intense laser pulses in the gas jets by optical field ionization was measured also by interferom-

etry and compared with tunnel ionization models.

Work partially supported by FCT (Portugal).

References

[1] Y.M. Li and R. Fedosejevs, Meas. Sci. Technol.5, 1197 (1994)

[2] D.B. Atkinson and M.M. Smith, Rev. Sci. Instrumen.66, 4434 (1995)

[3] K.A. Nugent, Applied Optics24, 3101 (1985)


Laser Wakefield Acceleration of Photons

C. D. Murphy1, 2

, R. M. G. M. Trines1, A. J. W. Reitsma

3, R. Bingham

1, 3, J. L. Collier

1, E. J.

Divall1, P. S. Foster

1, C. J. Hooker

1, D. A. Jaroszynski

3, K. Krushelnick

2, A. J. Langley

1, S. P. D.

Mangles2, J. T. Mendonça

1, Z. Najmudin

2, A. G. R. Thomas

2 and P. A. Norreys

1

1CCLRC - Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK, OX11 0QX

2Blackett Laboratory, Imperial College, London, UK, SW7 2AZ

3Department of Physics, University of Strathclyde, Glasgow, UK, G4 0NG

E-mail: [email protected]

ABSTRACT

Theory and simulation has for some time been able to predict that, under certain

circumstances, light can be up-shifted in frequency by a moving refractive index gradient. This

has previously been observed experimentally in the case of a relativistic ionisation front. The

effect has been considered as a possible method of diagnosis of a wakefield such as the one

postulated for a compact electron accelerator.

Here we present the first experimental observation of photon acceleration from a

laser-produced wakefield.

In our experiments, the Astra laser system at the Rutherford Appleton Laboratory was

focused into a supersonic jet of helium gas. 160mJ of the laser energy was delivered into a 25

micron focal spot in 40fs. The light that was transmitted through the interaction point was

collected and transported to a spectrometer which used reflective gratings to disperse the light.

The spectrum of the light was measured on a previously calibrated CCD camera.

We observe a blue shifted portion of the light which cannot be explained due to acceleration

from the ionisation front. A photon kinetic code has been implemented and can qualitatively

reproduce the measured spectrum. It demonstrates that this blue shifting occurs at the back of

the pulse, where the moving density gradient of the wake provides a time-varying refractive

index suitable for photon acceleration. The feasibility of using this effect as a wakefield

diagnostic will be discussed.


Field-shielding in femto- and picosecond laser accelerated ion beams

M. Schnürer1, S. Ter-Avetisyan1, E. Risse1, G. Priebe1, M.P. Kalachnikov1,

J. Tümmler1, K. Janulewicz1, W. Sandner1 and P.V. Nickles1 1 Max-Born-Institut, Berlin, Germany

Recently strong modulation have been found in the energy spectrum of protons emitted

off tiny water droplets which were irradiated by intense femtosecond laser pulses [1].

The modulations are ascribed to multi -temperature energetic electron components in

combination with an isothermal ion expansion model. Alternatively particle-in-cell

model calculations have been developed [2] which attribute the observed effect to the

interaction of different ion species in the laser accelerated beam. Consequently we will

discuss further experimental investigations in order to gain a better insight concerning

the action of different ions in an abruptly accelerated beam. Beside the spherical targets

thin foils have been irradiated with the two multi-Terawatt lasers of the MBI, a 35 fs

Ti:Sa – and a 0.8 ps Nd:Glass – system, which can deliver intensities in the focused

beam of up to 2x1019 W/cm2 and 4x1018 W/cm2, respectively. In comparison to already

reported influences of multi -species ions in laser accelerated beams we demonstrate a

new quality of field-shielding effects if ultrashort laser pulses are used to drive a proton

beam off a plane target foil . In its extreme a pure proton beam is emerging. In

dependence on the laser intensity distinct heavy ion species beside the protons are

found. In a simple field-shielding model we can use these tracer ions in order to

estimate the field acceleration parameters. Despite the low amount of heavy ions in the

proton beam a proton spectrum is found with an accentuated shape. It consists of two

branches which can be partly separated and which can be approximated by distinct

different temperatures. When the ps-laser pulse is used for the ion acceleration the

heavy ion background of the proton beam changes but the general spectral shape

remains: a decreasing number of protons up to approximately 1 MeV kinetic energy

which is followed by a step extending up to the cutoff at 4 MeV under our experimental

parameters. Summarizing we conclude that the build up electron distribution yields the

dominating influence on the proton spectra and field-shielding acts on heavier ions in a

mixed beam.

[1] S. Ter-Avetisyan et al., Phys. Rev. Lett. 93,155006(2004).

[2] A. Kemp and H. Ruhl, Phys. of Plasmas (2005) in press.


Particle acceleration with ultrashort light pulses P.V. Nickles, M. Schnürer, S. Ter-Avetisyan, S. Busch, E. Risse, M. Kalashnikov, G. Priebe,

J. Tümmler, K. Janulewicz, W. Sandner, U.Jahnke1) , and D. Hilscher1)

Max-Born-Institut, Berlin, 1) Hahn-Meitner Institut, Berlin

In a laser plasma driven by an ultra-short and highly intense laser pulse the laser energy can

be efficiently transferred to energetic electrons. These electrons can build up a strong charge

field, which in turn can accelerate ions to high energies approaching several tens of MeV and

carrying a significant part of the incident laser energy. Besides the irradiation conditions also

the target structures play a crucial role how effective this energy transfer into an energetic ion

beam can be. We report on experiments, where small isolated water and heavy water droplets

(20 micron in diameter) as well as plane Mylar and metalli c foils (10-20 micron thickness)

have been exposed with relativistically intense (~ 1019 W/cm2) laser pulses in order to study

ultrashort (~ 40 fs and 1 ps) laser pulse driven ion acceleration. Detailed investigations on

energy spectra and spatial distributions, generation efficiencies in dependence on the laser

pulse duration, intensity, and contrast result in scalings which can be used for a further

optimization of the ion “ beams”. Ions of several MeVs kinetic energy which carry a

significant part of the incident laser energy have been observed. A striking feature is the

appearance of strongly modulated ion energy distributions. This effect is still under

discussion, and -supposing one can control it- it might be useful for “monoenergetic”

ion/proton beam generation. We started for the first time investigations of the proton

generation from plane mylar foils using ~40 fs Ti:Sa laser pulses. The resulting ion energy

distributions will be interpreted in the frame of a picture where the acceleration field is

established extremely fast, leading of a massive shielding of the electric acceleration field

for the heavier ion species. Besides the “outward” directed emission caused by the TNSA

mechanism we studied also the “inflight” acceleration of deuterons in the dense plasma by

neutron TOF diagnostics relying on the known D(d,n) reaction. The angular resolved

detection of the absolute neutron yield and angular distribution allowed us for the specific

case of spherical microdroplet targets to infer that the deuterons inside the target are mainly

accelerated along the axis of the incident laser beam.

Finally, we introduce recent results on temporally resolved investigations of the high-energy

ion emission in dependence on both their charge states and energies using a newly developed

diagnostics consisting of a modified Thomson-parabola spectrometer with a pulsed electric

field. From our results we can conclude that all i ons were “born” instantaneously within the

experimental resolution limit (400-500ps) and they have been accelerated simultaneously by

the same electric field.


3D-PIC SIMULATIONS OF LASER ELECTRON ACCELERATION

Michael Geissler, and Jürgen Meyer-ter-Vehn

Max-Planck Institut für Quantenoptik, Hans Kopfermannstr. 1, D-85748, Garching,

Germany

The acceleration of electrons with high-intensity laser pulse is a highly complex nonlinear

process. Apart form fundamental physical questions, there exists considerable

technological interest for tunable compact electron source e.g. for x-ray lasers and fast-

ignitor fusion mechanisms. An efficient method is to accelerate electrons in an under dense

plasma. This Laser-wakefield acceleration was studied for laser pulses much longer than

the plasma wavelength. Recent simulations predict for laser pulse lengths comparable to

the plasma wavelength and laser intensities high enough for wave breaking a new

acceleration regime [1]. This “bubble” accelerated electron bunch has unique features e.g.

a peaked spectrum, high conversion efficiency and it is a self-organizing process. First

experiments at LOA [2] are consisted with these simulations but so far the bubble

acceleration regime was not reached. It is a new acceleration concept so several questions

are unsolved.

We present here results obtained with the 3D-PIC code ILLUMINATION for sub-10fs

Laser pulses. Scaling laws predict that the pulse duration is the key parameter for efficient

bubble acceleration [1]. The further simulation conditions are chosen to meet the Laser

parameter of the new LWS Laser system in Garching. The simulations indicate, that with a

100mJ, 5fsLaser pulse the bubble regime can be reached. Several problems will be

discussed e.g. influence of ionization, behavior of the electron bunch when the bubble

breaks down and influence of a prepulse.

[1] A. Pukhov, and J. Meyer-ter-Vehn, Appl.Phys. B (March 2002)

[2] V. Malka Science 298, 1597 (2002)


Numerical Study of K- Emission from the Backside of Foil Targets

Irradiated by Ultrashort Laser Pulses

O. Klimo1, J. Limpouch1

1Czech Technical University in Prague, FNSPE, Brehova 7, 115 19, Prague 1,

Czech Republic, email: [email protected]

Irradiation of solid targets by ultrashort laser pulse is accompanied by intense

X-ray line and continuum radiation emission. Namely K- radiation is of particular

interest in this context for its efficient generation, very short pulse, synchronization with

the laser pulse and high brightness. These properties predestinate it for application as a

diagnostic tool with unique subpicosecond temporal resolution and several experiments

have already successfully demonstrated its possibilities. As the K- emission is

primarily produced by fast electrons during their transport, it may also serve for study of

fast electron propagation in different targets, which is of great importance in the context

of Fast Ignition.

The generation of fast electrons, their transport and K- emission are studied

here by means of numerical simulations. The interaction of ultrashort laser pulse with

plasma layer on the surface of solid targets is treated by 1D3V relativistic

electromagnetic PIC code, which uses the boost frame for oblique incidence of the laser

beam. The code was enhanced to take into account variable ionization during the

interaction, which makes it possible to start with only slightly preionized target and to

follow the evolution of plasma. The transport of fast electrons in the colder dense part of

the target is modeled by our time-resolved 3D Monte Carlo code, which is specially

designed for simulations of K- emission.

K- emission from the backside of copper and aluminum foils is studied for

various foil thicknesses and different parameters of the laser plasma interaction. The

K- emission maximum is found for various laser plasma interaction regimes and the

size of the K- emission spot on both sides of the foil is calculated.

This work was partly funded by the Czech Ministry of Education, Youth and

Sports project No. 2471G1. The support by the Grant Agency of the Czech Republic

under project No. 202/03/H162 is gratefully acknowledged.


Interaction of an electron beam with magnetized semiconductor plates in

a rectangular waveguide

A. Rusanov, V. Yakovenko

Institute of Radiophysics and Electronics of the National Academy of Sciences of Ukraine,

Kharkiv, Ukraine

The paper presents a theoretical study of a non-relativistic electron beam interaction with

magnetized semiconductor plasma in a rectangular metal waveguide. Collisions of electrons are

taken into account. An electrostatic approach is used for investigation of the beam - plasma in-

teraction. Such an approach significantly simplifies the task and allows one to receive dispersion

equations in analytical form.

Plasma waveguide under consideration represents a rectangular metal waveguide partially

filled with semiconductor material placed in an external longitudinal magnetic field. We derive

the dispersion equation based on cold fluid model and numerically analyze it.

The results of the analysis show that plasma-beam interaction in such a structure gives rise

to a broad-band instabilities of the cyclotron waves and thespace charge waves (drift waves)

propagating along the beam - plasma interface. The growth rate of the drift instability attains

its maximum value under resonance conditions, when the frequency of the space charge wave

coincides with that of natural oscillations of the rectangular plasma waveguide.

References

[1] D. Bohm, E.P. Gross, Phys. Rev.75, 1864 (1949)

[2] I.N. Kartashov, M.V. Kuzelev, A.A. Rukhadze, Plasma Physics Reports30, 56 (2004)

[3] A.F. Rusanov, V.M. Yakovenko, Telecommunications and Radio Engineering57, 98

(2002)

[4] A.F. Rusanov, V.M. Yakovenko, MSMW’2004 Symposium Proceedings, 87 (2004)


Laser beam smoothing in plasma at powers below the filamentation

threshold

M.Grech1,2

, V.T.Tikhonchuk1, S.Weber

1, G.Riazuelo

2

1 CELIA, Université Bordeaux 1, 351 cours de la Libération, 33405 Talence, FRANCE

2 CEA / DAM / DIF / DPTA, BP 12, 91680 Bruyères-le-Châtel, FRANCE

The control of laser beam coherence is necessary to achieve a homogeneous

illumination on ICF targets. Standard optical smoothing techniques are limited by several

technological constraints. In last years, experiments have shown that the temporal coherence

of a spatially randomized beam is modified during its propagation through a low density

plasma. This could be an attractive possibility to improve the efficiency and quality of laser

energy deposition on targets.

We have proposed a statistical model to describe the coupling between random laser

field and induced density fluctuations. This model shows that spectral broadening of the laser

light is due to multiple scattering of the beam : each speckle creates either a local density

depression and a compression that propagates in a plane perpendicular to the laser

propagation direction and interacts with other speckles. This effect appears after a distance

that depends on both, the beam power and the number of hot spots. The coherence time of the

transmitted light is of the order of the characteristic time for plasma response that is of the

order of a few picoseconds. We show that there is an interesting regime where the non

stationary plasma density fluctuations induce the laser beam smoothing without exciting any

dangerous instability such as SBS or filamentation. The results of the statistical model are

confronted to the interaction code PARAX-MPL2D. The domain of validity is discussed.


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