Justifications for the measurement requirements related to fast ions in ITER ( action item 11a253)

F P ORSITTO ENEA Frascati

12th ITPA Princeton 26-30march2007

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Justifications for the measurement requirements related to fast ions in ITER

( action item 11a253)

Francesco Paolo Orsitto

ENEA C R Frascati



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Contributions

• Reference : • F P Orsitto, J-M Noterdaeme,A E Costley, A J H

Donne’ – IAEA FEC 2006 IT/P1-27



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Introduction

• Recent experiments on JET and JT60U have underlined the need to look into the parameter measurement requirements for fast particles on ITER:

• in particular the documented interaction of fast ions with AE and fishbones on JET and JT60U ( in particular the short time scales)

• In general the need to detect all the fast ions ( He4,p,T,He3) present in the plasma is proposed Because all of them can interact with AE, and this interaction could lead to a deterioration of confinement of fast ions and loss of efficiency of plasma heating.

• The electron distribution function is important as well to be detected and characterized: the deviation of electron d.f. from maxwellian play a central role in the Electron Cyclotron Heating and CD, and in the measurements of electron temperature.



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In weak shear plasma with large h

• Bursting AEs called Abrupt Large amplitude Events (ALEs)

In JT-60U, AE experiments have been performed utilizing Co-injected Negative-ion-based Neutral Beam (NNB)

(ENNB : 340 ~ 400keV, PNNB :3 ~ 5MW) in several kinds of magnetic shear plasma under combination with PNBs

JT-60U

results of AE studies in JT-60U

time scale : < msamplitude : large

In weak shear plasma with moderate h

time scale : 100ms ~ 1 samplitude : moderate

(h : energetic ion beta)



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0.4

0.5

0.6

0.7

0.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

t = 5.9s

Me

as.

/TO

PIC

S

r/a

t = 6.1s

0

2

4

6

8

10

5 5.5 6 6.5 7 7.5 8ne

utr

on

co

un

ts (

10

13 m

-2s

-1)

time (s)

-- r/a ~ 0.19 -- r/a ~ 0.32 -- r/a ~ 0.46 -- r/a ~ 0.56 -- r/a ~ 0.73 -- r/a ~ 0.84

NNB NNB

20

40

60

80

100

Fre

qu

ency

(kH

z)

The second channel signal increases rapidly

Local transport of energetic ions in the center region

qmin and q = 1.5 surface (TAE gap) both lie around r/a < 0.3

The innermost channel signal does not increase

Local transport of energetic ionsfor weak shear plasmas(Ishikawa IAEA 2006, EX/6-2)

In transition phase,

qmin=1.5



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outline

• Short Review of proposed new technical specs for fast particles

• Justification and discussion of the new requirements on measurements

• Analysis of the present status of the diagnostic systems proposed for ITER

• Conclusions and summary of R&D needed



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Introduction to classification of ITER diagnostics and

Review of ‘old’ technical specs for fast particles



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‘old’ technical specs for fast particles

• Alpha and He3 must be detected• Spatial resolution =a/10=20cm• Time resolution = 100ms• Accuracy 10-30%

Level 1 technical specs (september 2006): in blue the new tech specs



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Discussion of new technical specifications



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Tech Specs:physics basis

Above a critical fast (beta of fast particles), Alfvén cascades can be excited in a reversed shear discharge, giving rise to a spatial redistribution of fast particles over the minor radius in a time scale of

F ~ 100-300 A ~ 100-300 s (A = Alfvén time = R0/VA ~1s for a DT (50%/50%) in a ITER rev

Shear scenario, R0= major radius, VA = Alfvén velocity=B/(4ni mi)).

Indeed such a spatial redistribution on time scales,

similar to that calculated by theory, has been reported by JT-60U. (Shinohara NF2001, Ishikawa NF2005, Fogaccia et al EPS2006 Roma, G Vlad et al IAEA FEC2006)



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Relevant Time scales

• i) time scale related to the saturated non-linear interactions of energetic particles and Alfvén modes F ~ 100-300 A;

• ii) slowing down time of the fast ions sd ~0.2-0.5s;

• iii) confinement time E~ 4s ;

• iv) resistive relaxation time : R~ 200-300s.



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Relevant spatial scales

The relevant spatial scales in general are: i) Larmor radius fast ~ 0.2-7 cm; ii) Neoclassical Tearing Mode (NTM) island width ≥ ion

Larmor radius; iii) Internal Transport Barrier(ITB) width with spatial scale of

the order of the pressure gradient;iv) H-mode pedestal width ~ ion Larmor radius; v) turbulence correlation length ~ ion/electron Larmor

radius; the scaling of the confinement in H mode depends upon

the Larmor radius.



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Fast particle energy spectrum

• For slowing down distributions the energy range of fast ions is determined by the critical energy (E*) ,for energies E~E* , 50% of energy of fast ions goes directly the electrons and 50% to ions .

• E*(He3)~14Te, E*(D)=18Te,E*(H)=30Te, depending on the ion mass.

• For ITER(Te=20keV) the energy range important for the transfer of energy to electrons is :

• E*He3> 280keV,E*(D)>360keV,E*(H)>600keV



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Range of Larmor radius and slowing down time

of fast ions



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Tech specs

• the measurement requirements for fast particles could be proposed:

• i) spatial resolution ~ a/20 (10 cm on ITER) close to Larmor radius;

• ii) time resolution (minimum) ~ 100 A (~ 100 s for ITER);

• iii) density range of fast ions: the density of minority ions could be 4-10% of the plasma density



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(*)He0 neutralization proposed by M Sasao for alpha particle meas.

(*)

‘New’ requirements on measurements for fast particles



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Present motivations in Level1



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measurement of fast ion energy ( Motivations I: physics basis)

The measurement of the energy spectrum of fast particles is a fundamental quantity which enters the dynamics of transfer of energy between fast particles and bulk plasma.

The details of the distribution are important also in the context of the impact of evaluating the effect of various instabilities like Alfven Modes and fishbones on the confinement of fast ions and the efficiency of the transfer of energy to bulk plasma.

Not only the alpha particles and He3 ions are to be measured , but also protons, tritium and deuterium fast particles because they can interact with MHD modes, and participate to the global energy balance.



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Measurement of fast ion energy and spatial distr function

( Motivations II: spatial resolution)

• In general Not the same specs or measurement requirements for all ion species are needed , but the requirement shown in the table are minimal for all of them

• Spatial resolution- in particular : if the gyroradius is the fundamental quantity which determines the spatial resolution then a resolution of a/20 is a conservative evaluation( corresponding to alpha particles larmor radius) , (but a/30 could be more suitable, taking into account the gyroradius of all the fast ions).

• Category :The measurements are all in the category 1b or 2



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Measurement of fast ion energy and spatial distr. function

( Motivations III: time resolution)

• Time resolution: It would be ideal having time resolution of 100A which is the time scale of interaction with AE , but

• 1/10 of the slowing down time (~100ms) could be enough taking into account the difficulties of the diagnostics.



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Measurement of fast ion energy and spatial distr function

( Motivations IV: energy spectrum and density)

• The energy spectrum to be measured is • 0.1 < E < 3.5MeV• For ITER(Te=20keV) the energy range important for

the transfer of energy to electrons (Critical Energy) is :

• E*He3> 280keV,E*(D)>360keV,E*(H)>600keV

• Density range of fast ions: the density of minority ions could be 4-10% of the plasma density



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'old' 'new'

fast particles alpha, He3 alpha, He3, p ,D, T

spatial resolution a/10 a/20

time resol 100ms 100ms

energy range 0.1-3.5MeV 0.1-3.5MeV

accuracy 20% 20%



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Diag for confined fast ions-ray spectr.: it detects 1<E<5MeV, ( Be and C impurities are used) R&D needed to demonstrate the feasibility(rejection of n backgr by LiH

absorbers) in ITER . and new reactions must be explored for the detection of low energy ions.

2.CTS: nominally meets req.s; R&D needed to test the ITER concept in a real experiment; accuracy difficult to achieve in practice at the requested time resolution.

3.CXRS: spatial resolution and accuracy not achievable for r<0.3.

4.NPA : no spatial resolution.energy and time resolution achievable.

In The range of energy of fast particles 0.1<E<1000keV in practice no proven technique exists which meet all the requirements



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Dia for fast particles: ray spectroscopy

1. it detects 1<E<5MeV, 2.Alphas are detected using Be as impurity: 9Be(,n)12C(E=4.44MeV) 3.Deuterons are detected using 12C(d,n)13C(E=3.1MeV) 4. He3 are detected using 12C(He3,n)14N(E=2.31MeV,5.1MeV)

5.R&D needed to demonstrate the feasibility in ITER : rejection of n backgr by LiH absorbers

6.In practice ( looking to JET experience) the required accuracy is difficult to achieve ;

The integration time needed is in the range of 100ms: so definitely the gamma ray spectroscopy Could see the slowing down of fast ions , but not the fast spatial redistribution due to the interaction with the Alfven modes.

7.



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Collective Thomson Scattering• The CTS proposed uses a gyrotron at 60GHz , applying the principle that

using a source at a frequency below the first harmonic of ECE is beneficial to lower the plasma background temperature. The system proposed has the capability of measuring ions with velocity parallel and perpendicular to the magnetic field.

• The spatial resolution is 20cm ( i.e. a/10) and the time resolution is 100ms, with an accuracy of 20%.

• The energy spectrum to be measured has been specified (0.1-3.5MeV) .

• The main difficulty of CTS is that in principle it cannot distinguish between ions with the same Z/M.

CTS: nominally meets req.s; R&D needed to test the ITER concept in a real experiment; accuracy difficult to achieve in practice at the requested time resolution.

Presently CTS experiments on FTU and ASDEX



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CTS sources



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Present motivations in Level 1



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measurement of fast particle losses

( motivations I: physics basis)• The measurement of fast particle losses have important

implication on the machine safety (because the fast particle lost could damage the wall), for the measurement of the effects of MHD instabilities on the confinement of fast ions.

• The losses of particles have a strong impact on the global confinement properties of the discharges as it has been demonstrated in series of experiments related with the variation of the ripple losses on JET , and JT60U.

• Classification : the diagnostic of fast particle losses is important for safety of the machine - it must be put in the diag set 1a for machine control and safety



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Measurement of fast particle losses( motivations II: space , time resolution and energy

spectrum)• Spatial resolution : the system could be built as an array of

detectors covering some poloidal region, so the poloidal angle could be specified . The proposed poloidal distance is a/20.

• Time resolution is enough to detect fast events.Whether the time resolution of 0.1-0.5ms is achievable:it depends on the sensors.With scintillator probes this could be easily achievable

• The energy spectrum depends on the resolution of the measured gyroradius ~(E)1/2 / B: ~70mm for 3.5MeV alpha part., a resolution of 10% in , means 20%in energy. In JET for example a 15% resolution on gyroradius can be achieved, with the scintillator probe.



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'old' 'new'escaping fast particles

alpha, He3

alpha, He3, p ,D, T

spatial resolution a/10 a/20time resol 100ms 0.1-0.5msenergy range

not defined

0.1-3.5MeV

accuracy 10-30% 20%



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Diagnostics • Faraday Cups (FC) and Scintillator probes(SP) were already tested

on JET and TFTR. • The JET FC system measures the poloidal distribution of lost fast

ions with a course energy resolution. Alpha particles in the range of 1-3 MeV can be detected with an energy resolution of the order of 10-15% .

• The SP measures the gyroradius and pitch angle of a fast particle, the accuracy of measurement of gyroradius is 15%, while that of the pitch angle is 5%, the time resolution is 0.1ms.

• systems as scintillators and Faraday-cups are subject to failure in the high radiation fields at ITER.

• Preliminary analysis lead to consider other systems like ceramic

scintillators and infrared multifoil thermal detectors



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Infrared viewing bolometers • Infrared viewing bolometers (IRVBs)

with absorber foils of varying thickness to measure the intensity and energy distribution of escaping -particles have been successfully tested at JT-60U [[i]].

• The first images from these bolometers are reasonably consistent with images obtained with resistive bolometers. The IRVBs can operate in a reactor environment and prospects for their utilization in ITER are optimistic.

•[i] B. Peterson, presented at the 11th Meeting of the ITPA Topical Group on Diagnostics, Sendai, 2006.



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Level 1 requirements on neutron



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measurement of neutron distribution and spectrum ( motivations I)

• the spatial resolution of a/20 (10cm) is achievable with the present camera(s), in particular if a vertical camera is included.( preliminary study by L Petrizzi and B Esposito)

• the time resolution of 0.1-0.5ms is achievable with the presently available ( still under test) electronics which is able to discriminate the neutron from gammas.

• are the specs achievable also for neutron energy spectrum measurements?:

• the compact neutron spectrometers based on scintillators likely not

• CVD can achieve the time resolution required.



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neutrons old' new'spatial resolution a/10 a/20time resol 1ms 0.1-0.5msenergy range

not defined TBD

accuracy 10% 10%



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Conclusion and R&D • New technical specs are derived from physics of alfven wave

interaction and the necessity of measuring all the fast ions.

• Intensive R&D is needed to demonstrate the feasibility of• ray spectroscopy, • Collective Thomson Scattering ,• neutron fast electronics, • neutron compact spectrometers, • CXRS• Escaping fast ions sensors : multifoil bolometers ,

• Diagnostics capability for fast ions with energy in the range between 0.1Mev and 0.6 MeV and lost fast particle diagnostics needs urgently to be improved



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Slides for discussion



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Typical data on distribution functions on fast ions in ITER



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Heating systems in ITER



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Neutronics for ITER

• A study has been done about the possibility for the ITER neutron camera to meet the requirements ( L Petrizzi SOFT sept2006 and B Esposito ), the code used has been prepared for the task EFDA EFDA/04-1209 for RNC

• Parameters assumed :• DT full power (scenario 2),• diameter of collimators 2 cm in-vessel and 1 cm ex-

vessel (corrisponding to 1-2 MHz max , count rate sostainible by the detectors),

• 0.1 ms time resolution • Detector efficiency 1%.



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Neutronics for ITER

• The code used for the design of the ITER RNC has produced the Abel inverted neutron emissivity , assuming the equilibrium of ITER, the emissivity constant on the magnetic surfaces and the actual configuration of the line of sights of ITER RNC. For the case of 0.1ms time resolution.

• The reconstructed emissivity for 0.1ms time resolution is divided To that in normal conditions ( 10ms) , and this ratio is determined versus the flux coordinate.

• It is detected that the accuracy on the emissivity is inside 20%.



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The reconstructed emissivity for 0.1ms time resolution is divided To that in normal conditions ( 10ms) , and this ratio is determined versus the flux coordinate.

Documents

Justifications for the measurement requirements related to fast ions in ITER ( action item 11a253)