Supported by

College W&MColorado Sch MinesColumbia UnivComp-XGeneral AtomicsINELJohns Hopkins UnivLANLLLNLLodestarMITNova PhotonicsNew York UnivOld Dominion UnivORNLPSIPrinceton UnivSNLThink Tank, IncUC DavisUC IrvineUCLAUCSDUniv ColoradoUniv MarylandUniv RochesterUniv WashingtonUniv Wisconsin

Culham Sci CtrUniv St. Andrews

York UnivChubu UnivFukui Univ

Hiroshima UnivHyogo UnivKyoto Univ

Kyushu UnivKyushu Tokai Univ

NIFSNiigata UnivUniv Tokyo

JAERIHebrew Univ

Ioffe InstRRC Kurchatov Inst

TRINITIKBSI

KAISTENEA, Frascati

CEA, CadaracheIPP, Jülich

IPP, GarchingASCR, Czech Rep

Univ Quebec

New Capabilities and Results for the

National Spherical Torus Experiment

M.G. BellPrinceton Plasma Physics Laboratoryon behalf of the NSTX Research Team

presented at theJoint Meeting of the

3rd IAEA Technical Meeting and the

11th International Workshop on

Spherical TorusSt. Petersburg, Russia

Oct. 3 – 6, 2005

Bell, M. / STW’05 / 051003

2

NSTX Just Completed 18 Weeks of Experiments Exploiting New Capabilities

and Regimes

• Good performance of TF coil joints: ~2500 pulses, 75% at 0.45T or higher

– Operated to 95% of design field (0.6T) at end of run

– Joint resistances remained below expectations

• Extensive investigation of Coaxial Helicity Injection

– Higher capacitor bank voltage (1.5kV) and localized gas injection

• New PF1A coils for simultaneous high triangularity and high elongation

• Three pairs of magnetic field perturbation coils

– Powered by fast Switching Power Amplifiers for Error-Field Correction and Resistive Wall Mode control

• Lithium Pellet Injector, Supersonic Gas Injector

– LPI used both for plasma perturbation experiments and Li coating

• Movable Glow Discharge electrode

– More uniform coverage and operation at lower gas pressure

Bell, M. / STW’05 / 051003

3

Coaxial Helicity Injection Experiments Benefited from New

Capabilities

•Inject gas and microwave power into chamber beneath injector gap

– Reduced total gas requirement for breakdown

•Capacitor bank with fast crowbar and higher voltage for coil producing initial flux

– Operated bank at up to 1.5kV

– Force reconnection to produce closed flux

•Fast cameras to observe plasma on closed flux surfaces

Gas, ECH Injection

Injectorcurrent

– )| +Capacitor bank

10 – 50 mF, 1 – 2 kV

Insulated gaps between inner, outer divertor

plates

Poloidal fieldlinking platesToroidal

fieldCL

Bell, M. / STW’05 / 051003

4

CHI Produced Persistent Current and Closed Flux For ~10ms After the

Injector Current Pulse

17 ms15 ms

13 ms11 ms

9 ms7.5 ms

• Need to develop transition to control of toroidal equilibrium R. Raman, B. Nelson (U. Wash.), R. Maqueda (Nova), B. LeBlanc 

5101520010120100Time (ms)Injector Voltage (kV)Injector Current (kA)Toroidal Plasma Current (kA)Times of Thomsonscattering data

Time of capacitorbank crowbar

118340 

Radius (m)0.51.01.500.51 t = 13 ms15 ms

Electron density (1019m-3)0.51.01.501020 t = 13 ms15 ms

118340 Electron temperature (eV)118340 

Bell, M. / STW’05 / 051003

5

Motional Stark Effect Diagnostic Routinely Measures Magnetic Field Line

Pitch

• 8 channels span from outer edge past magnetic axis• Calibrated by NBI into neutral gas with known applied fields

• EFIT provides between-shots analysis for q-profile– Can include correction for Er using CHERS v profile

– Also applying LRDFIT, ESC equilibrium codes

RMS error 0.4°

Radius (m)

Pitch angle (degrees) +40

+30

+20

+10

0

-100.9 1.0 1.1 1.2 1.3 1.4 1.5

MSE data

EFIT analysis

F. Levinton, H. Yu ( Nova Photonics), S. Sabbagh (Columbia U.) 

Bell, M. / STW’05 / 051003

6

0.51.01.5Radius (m)0.00.51.00.00.51.0neTiTenDkeV1020

m-30.75s1178140.75s

51-Channel Charge-Exchange Recombination Spectroscopy Reveals

Extreme Gradients

•Diagnostic measures Ti(R), v(R), nC(R)

– Infer nD(R) under assumption that carbon is dominant impurity

Radius (m)

Toroidal velocity (km/s)

1.3 1.4 1.5

150

100

0

50

MPTS

R. Bell, B. LeBlanc

Bell, M. / STW’05 / 051003

7

New Inboard Divertor Coils Increase Accessibility of High-Triangularity,

High-Elongation Shapes

• Highest = 2.7 now obtained at highest ≈ 0.8 S q95 IP/aBT = 35 MA/m·T

– Record stored energy = 430kJ at IP = 1.4MA, N = 5.3, T = 29%, q* = 2.3

• Small ELM regime recovered at high > 2.5 with new coils– Previously observed onset of large ELM-like events when > 2.2

2004 2005

New PF1A coilOld PF1A coil

All values at

MAX(T) > 20%

WMHD = 430kJ

at IP = 1.4MA

2004 2005

J. Menard, D. Gates

Bell, M. / STW’05 / 051003

8

Record Pulse-Lengths Achieved at Moderate Current by Operating with

Sustained H-mode

•H-mode with small ELMs lower flux consumption, slow density rise

•High P increases bootstrap fraction lower flux consumption

N

IP (MA)

VSURFACE (V)

T = 17%P = 1.5, li =

0.65

Current Relaxation

Time (s)

ne / nGW

= 2.3, L = 0.75

E

H89P = 2-2.2

H98(y,2) = 1-1.1

PNBI (MW) / 10

J. Menard 

Bell, M. / STW’05 / 051003

9

Low Loop-Voltage Quiescent Phase Ends at Onset of Saturated n=1 Mode When qmin

1

•Saturated n=1 mode persists for 0.5s

•Central rotation drops by factor 3

•Edge f maintained

• N decreases

– N = 6 above no-wall limit

– N = 4 below no-wall limit?

•qmin sustained near 1

– No sawteeth observed

– Similar to hybrid mode

Time (s)

Core f (kHz)

Edge f

N

PNBI = 6MW

qMIN

qMIN without Er correction

J. Menard, F. Levinton, S. Sabbagh 

Bell, M. / STW’05 / 051003

10

Long Duration Discharges Exceed 70% Non-Inductive Current During High-

Phase

•TRANSP model agrees with measured neutron rate during high-phase

•TRANSP over-predicts neutron rate early and late when low-f MHD present– Fast-ion diffusion and/or loss likely

– Assessing impact on JNBI profile and q-profile

•85% of non-inductive current is p-driven– Bootstrap + Diamagnetic + Pfirsch-Schlüter

0.00.51.01.50.00.50.01.02.00.00.5DD neutronrate (1014s-1)Fraction of

total currentFraction of total energy

IonsBeam ionsElectronsInductiveBootstrap (Sauter)Beam-driven∇pMeasuredModeledTRANSP116313 03A

0.01.02.0P< >EFIT( )Time s

Bell, M. / STW’05 / 051003

11

Also Extended Pulse Length at Higher Current

•At high Ip, contribution reduced from– bootstrap current (fBS 1/2P)

– NB-driven current (higher density)

0.51.01.5Radius (m)0.00.51.00.00.51.0neTiTenDkeV1020

m-30.75s1178140.75s00.51010100.51Time (s)keV1020

m-3V0101Ip (MA)VsurfPne(0)<ne>Ti(0)Te(0)117814PNBI( )/10MW-H mode

WMHD=430kJ

BT = 0.45T

T = 29%

J. Menard, D. Gates

Bell, M. / STW’05 / 051003

12

Lithium from Injected Pellets Deposited on Plasma-Facing Surfaces Provides Edge

Pumping

•Fired lithium pellets (1.7 – 5 mg) from multi-barrel pneumatic injector into sequences of ohmically-heated helium discharges– Limited on center-stack tiles or lower-single-null divertor

– After “pre-conditioning” surfaces with OH helium plasma

– 1 or 2 pellets per discharge, 24 – 30 mg total lithium in each sequence

•Dramatic reduction in density in 1st subsequent NB-heated deuterium gas-fueled discharge (~3.5mg D2) in both configurations

0.00.51.01.50.24 – 0.28 s0.51.01.5ne(1019m-3)

Ist shotafter LiBefore Li(after He)Radius (m)0.00.51.00.00.10.20.30.40.5Time (s)<ne>

(1019m-3)Before Li(after He)3rd after Li2nd after Li1st after Li (25mg)0.8MA, 0.45T, divertor discharges, deuterium gas fueled (~4mg/shot)Gas off,plasmadiverted

•Effect disappeared by 3rd similar discharge– Expected if most injected gas reacts with deposited lithium H. Kugel 

Bell, M. / STW’05 / 051003

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External Radial Field Coils Used to Counteract Effects of Intrinsic Error

Fields

• Investigated threshold for occurrence of locked-modes in low-density, low- discharges as magnitude and direction of radial field varied

VALEN (Columbia Univ.)

6 ex-vessel coils(1.6m2 2 turns each)48 in-vessel sensors

(B, B)

Inferred intrinsicerror fieldB 2,1 = 1.3G

EF = 140º

ne at q=2

~41018m-3

• IP=0.7MA• BT = 0.45T• q(0) =1.1-1.5 (no sawteeth)

3 SPAs 3.3kA3.5kHz

J. Menard

Bell, M. / STW’05 / 051003

14

Applying n=1 Correction Field with External Coils Extended Pulse Length at

High N

•With field in “non-correcting” directions, rotation is damped – Earlier island locking and/or RWM formation•In “correcting”

direction, near-edge rotation collapse is avoided– Extends pulselength at high-

117577

117571

f

(carbon)

J. Menard, S. Sabbagh, R. Bell 

Bell, M. / STW’05 / 051003

15

Applied n = 3 Stationary Field Used to Control

Plasma Rotation Reversibly

•Rotation stops completely in vicinity of resonant q = 3 surface

– Neoclassical toroidal viscosity affects inner region

•Rotation can recover if RWM is not destabilized W. Zhu, S. Sabbagh, R. Bell

Bell, M. / STW’05 / 051003

16

Repetitive Bursts of MHD Activity Affect

Fast Ion Population During NBI Heating

• Bursts of MHD activity detected by Mirnov coils are kinetic instabilities driven by population of fast ions

– Instabilities chirp in frequency

– Toroidal mode numbers n = 2 – 6

• Bursts are coincident with rapid drops in DD neutron rate

– Mainly beam-target reactions

• NPA measures energy and pitch angle resolved effect on fast ions

– Depleted over wide energy range

– No D spikes to suggest changes in edge neutral density

E. Fredrickson, S. Medley 

Bell, M. / STW’05 / 051003

17

Robust Reversed-Shear Startup by Varying

Ramp-Rate, NB Timing and Gas Injection

q profile (LRDFIT with MSE)0.00.10.20.30.4Time (s)100210100200Ip (MA)PNBI (MW)WMHD (kJ)115731115730

•q-profile very dependent on early MHD acitivity

– Events lead to monotonic profile

•Also combined RS with H-mode edge but not yet optimized F. Levinton (Nova), J. Menard 

Bell, M. / STW’05 / 051003

18

Reversed-Shear Appears to Produce an Electron Transport Barrier

• e reduced by ~2 in confinement zone

• HHFW heating also raised central Te in RS

00.51√ΦNe(m2s-1)100101115730,0.296s115731,0.326s±0.025Average sVariation±0.025sTRANSP with classical NB thermalization

F. Levinton (Nova), R. Bell, B. LeBlanc, S. Kaye

3210Ti (keV)115730, 0.296s115731, 0.326s210Te (keV)115730, 0.293s115731, 0.327s420ne (1019m-3)115730, 0.293s115731, 0.327s0.51.01.5Major radius (m)

Bell, M. / STW’05 / 051003

19

Newly Installed High-k Scattering Diagnostic Will Probe Turbulence Related to Electron Transport

• = 1mm probe beam launched tangentially near midplane

•Inboard / outboard launch configurations– kr = 0 – +20 cm-1 (in), -20 cm-1 (out)

•Superheterodyne receivers (UC Davis)– Five channels with NF of ~3000oK

•First scattered signals at end of 2005 runOutboardLaunch

InboardLaunch

0 500 kHz-500Amplitude (arb.)

Fourier transform of scattered signalOutboard launch, kr = -15cm-1

Shot 118148t=200ms

H. Park, D. Smith, E. Mazzucato, C. Domier (UCD)

Bell, M. / STW’05 / 051003

20

MSE Shows Evidence for Formation of “Current Hole” in NSTX

•At 0.12 s current profile is hollow but central current density is finite

•Small region of almost zero current density forms at 0.13 s

•Expands to about 15 cm diameter by 0.20s

•Central current density becomes positive again by 0.24 s

F. Levinton, H. Yu (Nova) 

Bell, M. / STW’05 / 051003

21

Investigating Aspect-Ratio Dependence of

H-mode Pedestal in Experiment with MAST, DIII-D

•Also studying H-mode threshold in MAST/NSTX

ne [1019m-3] Te [keV]

tot [%]

N

Ti [keV]

e

NSTX (117723@427ms) DIII-D (121516@1175ms) MAST (12899@270ms)

Cross-sections projected onto NSTX equilibrium

R. Maingi (ORNL), A. Field (MAST), H. Meyer (MAST), T. Osborne (DIII-D)

Bell, M. / STW’05 / 051003

22

Puffing Deuterium into Private Flux Region Reduces Outer Divertor Heat Flux

by Factor 2–4

•No change in inner divertor heat flux - inner leg already detached

•Evidence for volume recombination from increase in D/D ratio– Divertor radiation increases but not spatially resolved

•Outer divertor detachment not achieved by midplane injection of D2 or Ne– Ne did reduce divertor heat flux by factor 4 by plasma and SOL radiation

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.0

-1

-2

1(m)

2

0 2 (m)1D2

D2 fueling rate (1021/s)Peak heat flux on outer divertor

(MWm-2)

Ip = 0.7MA, BT = 0.45T, PNBI = 3–4MW

V. Soukhanovskii (LLNL) 

Bell, M. / STW’05 / 051003

23

NSTX Made Significant Progress in 2005

•Clear demonstration of persistent current initiated by CHI

•Extension of operating regime at high and •First experience with full set of Error Field Correction and RWM Control coils– Cancellation of intrinsic error fields– Control of rotation and effect on mode growth

•Significant extension of pulse-length at moderate current

•Exploration of reversed-shear regime– Beneficial effect on electron confinement

•Demonstration of particle control with lithium coating in both limiter and divertor plasmas

•Contributions to physics of H-mode, ELMs, pedestal, confinement– Collaborative experiments and participation in ITPA

Bell, M. / STW’05 / 051003

24

Status and Plans

•Now entering an outage planned to last until December 2005

– Install in-vessel components for “poloidal CHERS” diagnostic

•Opposing vertical views across NB path to measure vpol and Ti

– Install lithium evaporator for coating areas of divertor and wall

•Build on experience in LTX (former CDX-U) and with LPI in NSTX

– Examine all TF coil joints and refurbish if necessary

•NSTX 2005 Results Review and Research Forum for planning experiments in 2006 will take place December 12 – 16

– Participation by our collaborators is encouraged

– Length of 2006 experimental run is not yet known

•Awaiting outcome of budget negotiations in US Congress