Confinement and Local Transport in the National Spherical Torus Experiment (NSTX)

Stanley M. Kaye1, M.G. Bell1, R.E. Bell1, C. W. Domier2, W. Horton3, J. Kim3, B.P. LeBlanc1,

F. Levinton4,N.C. Luhmann2, R. Maingi5, E. Mazzucato1, J.E. Menard1, D.R. Mikkelsen1,

H. Park1, G. Rewoldt1, S.A. Sabbagh6, D. Smith1, D. Stutman7, K. Tritz7, W. Wang1, H. Yuh4

21st IAEA/Fusion 2006 MeetingOct 16 – 21, 2006Chengdu, China

1 PPPL, Princeton University, Princeton, NJ, USA 085432 University of California, Davis, CA, USA 95616

3 IFS, University of Texas, Austin, TX, USA 787124 Nova Photonics Inc., Princeton, NJ, USA, 08540

5 ORNL, Oak Ridge, TN, USA 378316 Dept. of Applied Physics, Columbia University, NYC, NY, USA 10027

7 The Johns Hopkins University, Baltimore MD 21218

Supported byOffice ofScience

Culham Sci CtrU St. Andrews

York UChubu UFukui U

Hiroshima UHyogo UKyoto U

Kyushu UKyushu Tokai U

NIFSNiigata UU Tokyo

JAERIHebrew UIoffe Inst

RRC Kurchatov InstTRINITI

KBSIKAIST

ENEA, FrascatiCEA, Cadarache

IPP, JülichIPP, Garching

ASCR, Czech RepU Quebec

College W&MColorado Sch MinesColumbia UComp-XGeneral AtomicsINELJohns Hopkins ULANLLLNLLodestarMITNova PhotonicsNew York UOld Dominion UORNLPPPLPSIPrinceton USNLThink Tank, Inc.UC DavisUC IrvineUCLAUCSDU ColoradoU MarylandU RochesterU WashingtonU Wisconsin

SMK – 21st IAEA 2

NSTX Addresses Transport & Turbulence Issues Critical to Both Basic Toroidal Confinement and Future Devices

• NSTX offers a novel view into plasma T&T properties– NSTX operates in a unique part of

dimensionless parameter space: R/a, T, (,

– Dominant electron heating with NBI: relevant to -heating in ITER

Major Radius R0 0.85 mAspect Ratio A 1.3Elongation 2.8Triangularity 0.8Plasma Current Ip 1.5 MAToroidal Field BT 0.55 TPulse Length 1.5 sNB Heating (100 keV) 7 MWT,tot up to 40%

– Excellent laboratory in which to study electron transport: electron transport anomalous, ions close to neoclassical

– Large range of T spanning e-s to e-m turbulence regimes

– Strong rotational shear that can influence transport

– Localized electron-scale turbulence measurable (e ~ 0.1 mm)

SMK – 21st IAEA 3

This Presentation Will Focus on Confinement & Transport Trends in NSTX and Their Underlying Processes

• Major accomplishments– Key confinement and transport dependences established (BT, Ip, , , q(r),

…)

– High priority ITPA tasks have been addressed

• Dimensionless parameter scans in Te

• Established more accurate (=a/R) scaling with NSTX (& MAST) data included in the ITPA database

98y2~Ip0.93 BT

0.15 ne0.41 P-0.69 R1.97 0.58…

new~Ip0.73 BT

0.36 ne0.39 P-0.62 R2.14 1.03 (Kaye et al., PPCF 48 [2006] A429)

– Localized turbulence characteristics being assessed across wide range of k (upper ITG/TEM to ETG)

– Theory/simulations have indicated ETG modes could be important in controlling electron transport

SMK – 21st IAEA 4

Dimensionless Parameter Scans Have Addressed High-Priority ITPA Issues

-scan at fixed q, BT

- -dependence important to ITER advanced scenarios (B98y2~-0.9) - Factor of 2-2.5 variation in T

- Degradation of E with weak on NSTX

20% variation in e, e*

e-scan at fixed q

- Factor of >3 variation in e*

- Strong increase of confinement with decreasing collisionality

=2.1=0.6

SMK – 21st IAEA 5

Dedicated H-mode Confinement Scaling Experiments Have Isolated the BT and Ip Dependences

Scans carriedout at constantdensity, injectedpower (4 MW)

0.50 s 0.50 s

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Dedicated H-mode Confinement Scaling ExperimentsHave Revealed Some Surprises

Strong dependence of E on BT

E,98y,2 ~ BT0.15

H98y,2 ~ 0.9 → 1.1 → 1.4

4 MW

E,98y,2 ~ Ip0.93

H98y,2 ~ 1.4 → 1.3 → 1.1

Weaker dependence on Ip

E~Ip1.3-1.5 at fixed q E,98y,2~Ip

1.1 at fixed q

NSTX E exhibits strong scaling at fixed q

4 MW

SMK – 21st IAEA 7

Variation of Electron Transport Primarily Responsible for BT Scaling

Broadening of Te & reduction in e outside r/a=0.5 with increasing BT

Ions near neoclassical

Neoclassical

SMK – 21st IAEA 8

Theory/Gyrokinetic Calculations Suggest ETG May Play an Important Role in Determining Electron Transport at Low BT

Non-linear simulations indicate formation of radial streamers (up to 200e): FLR-modified fluid code [Horton et al., PoP 2005]

• Good agreement between experimental and theoretical saturated transport level at 0.35 T

• Experimental e profile consistent with that predicted by e-m ETG theory [Horton et al., NF 2004] at 0.35 T

• Not at higher BT

Kim, IFS

ETG linearly unstable only at lowest BT

- 0.35 T: R/LTe 20% above critical gradient - 0.45, 0.55 T: R/LTe 20-30% below critical gradient

0.35 T

GS2

SMK – 21st IAEA 9

Ion Transport Primarily Governs Ip Scaling- Ions Near Neoclassical Level -

i,GTC-NEO

(r/a=0.5-0.8)

GTC-Neo neoclassical: includes finite banana width effects (non-local)

SMK – 21st IAEA 10

Turbulence Measurements + Gyrokinetic Calculations Have Helped Identify Possible Sources of Transport

Ion transport duringH-phase isneoclassical

Microwave scattering system measuresreduced fluctuations (n/n) in both upperITG/TEM and ETG ranges during H-mode

~

Electron transportreduced, but remainsanomalous

Ion and electron transport changegoing from L- to H-modes

- Localized measurement (axis to edge)- Excellent radial resolution (6 cm)

ELMs

SMK – 21st IAEA 11

Theory/Gyrokinetic Calculations Indicate Both ITG/TEM and ETG are Possible Candidates for Electron Transport

GS2 calculations indicate lower linear growth rates at all wavenumbers during H- than during L-phase: ETG unstable

Experimental e profile consistentwith that predicted by e-s ETG theory(Horton et al, Phys. Plasmas [2004])

Non-linear GTC resultsindicate ITG modesstable during H-phase;i ~ neoclassical

SMK – 21st IAEA 12

NSTX Plays a Key Role in Multi-Scale Transport & Turbulence Research

• Confinement and transport trends found to differ from those at higher R/a– Strong BT, weaker Ip scaling

• Electron transport variation primarily responsible for BT scaling

• Ions near neoclassical; primarily responsible for Ip scaling

• Understand the source of the difference in confinement trends at different R/a (low vs high-k turbulence dominant at different R/a, BT?)

• Data provided to ITPA H-mode database for R/a and T scalings

– No degradation of BE with T

• n/n decreases from L- to H-phase for kr=2 to 24 cm-1 (upper ITG/TEM to ETG range) – Associated with reduction in transport

• Linear and non-linear theory have indicated ETG modes could be important– Need also to consider lower-k modes

(microtearing, ITG/TEM)

~

SMK – 21st IAEA 13

Backup Vugraphs

SMK – 21st IAEA 14

New Diagnostic Capabilities Have Facilitated Progress in Understanding Transport Processes

12 channel MSE [NOVA Photonics]

LRDFITReconstruction

Rmag

51-point CHERS 20-point MPTS

Tangential microwave scattering measureslocalized electron-scale turbulence

• kr=2 (upper ITG/TEM) to ~24 (ETG) cm-1

• e ~0.01 cm• r ~ 6 cm• k ~ 1 cm-1

• Can vary location of scattering volume (near Rmag to near edge)

Important for equilibrium and microinstability calculations

SMK – 21st IAEA 15

New Diagnostic Capabilities Have Facilitated Progress in Understanding Transport Processes

Tangential micorwave scattering measureslocalized electron-scale turbulence

12 channel MSE [NOVA Photonics]

LRDFITReconstruction

Important for equilibrium and microinstability calculations

• kr=2 (upper ITG/TEM) to ~24 (ETG) cm-1

• e ~0.01 cm• r ~ 6 cm• k ~ 1 cm-1

• Can vary location of scattering volume (near Rmag to near edge)

SMK – 21st IAEA 16

Dimensionless Variable Scans Have Addressed HighPriority ITPA Physics Issues (- scaling)

-scan at fixed e, e*

- -dependence important to ITER advanced scenarios (B98y2~-0.9) - Degradation of E with weak on NSTX

NSTX data used in conjunction with ITPA data to establish (=a/Rscaling with more confidence

ITER98PB(y,2) scaling does not represent low R/a data well

98y2~Ip0.93BT

0.15ne0.41P-0.69R1.970.58…

new~Ip0.73BT

0.36ne0.39P-0.62R2.141.03

(Kaye et al., PPCF 48 [2006] A429) 2-2.5 variation in T

20% variation in e, e*

SMK – 21st IAEA 17

Stronger Reversed Magnetic Shear Is Associated with Reduced Transport

Weak vs Reverse-Shear L-mode Global non-linear GTC and GYRO simulations show that a pure ITG mode is unstable without ExB flow shear included

TEM & ETG calculations underway

SMK – 21st IAEA 18

Pellet Perturbations Are Being Used to Probe Relation of Critical Gradient Physics to q-Profile

H-mode with monotonic q-profile exhibits stiff profile behavior → Te close to marginal stability

Reversed magnetic shear L-mode responds to pellet perturbationover several ms

Soft X-ray arraydiagnoses fast Te

R/LTe

t=297→301 ms

R/LTe

t=440→444 ms

Stutman, JHU