SMK – RR ‘07 1

Beta Scaling and Momentum Transport Studies

XPs 713 & 723

S.M. Kaye

NSTX Results ReviewJuly 23-24, 2007

PPPL, Princeton University

Supported byOffice ofScience

Culham Sci CtrU St. Andrews

York UChubu UFukui U

Hiroshima UHyogo UKyoto U

Kyushu UKyushu Tokai U

NIFSNiigata UU Tokyo

JAERIIoffe Inst

RRC Kurchatov InstTRINITI

KBSIKAIST

ENEA, FrascatiCEA, Cadarache

IPP, JülichIPP, Garching

ASCR, Czech RepU Quebec

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

SMK – RR ‘07 2

XPs Performed to Study Different Transport Properties in NSTX

• XP713Beta Scaling– High priority ITPA task – important to success of ITER AT scenario– Follow on from last year’s beta scaling results

• Power scan at =2.1, =0.8 discharges showed no degradation of confinement with beta

– Consistent with JET, DIII-D results with strong shaping– Inconsistent with JT-60U, AUG results with weaker shaping

– Redo similar power scan but with weaker shaping (k=1.8-1.9, d=0.4)– Completed in ½ day

• XP723Momentum Transport Studies (w/W. Solomon)– Statistical studies show and i decoupled

• Unlike at conventional aspect ratio where ITG is important

– Momentum diffusivity low– Experiments to study steady-state momentum transport

• Use perturbation technique with n=3 field blips (non-Resonant Magnetic Perturbations) to separate from vpinch

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Dimensionless Parameter Scans Have Addressed High-Priority ITPA Issues – Beta Dependence of Confinement

-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*

=2.1=0.6

Test shape dependence with similar power scan - =1.8-1.9, ~0.4 - e

, vary ≤ 20% across scan

- ELM severity increased with increasing power • Only few % loss per ELM • High frequency ELMs at low power (Type III?)

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Observed Weak Increase of Beta With Power

Type III ELMs severely degrade confinement

Strong degradation of E (E ~ T

-1.0)

Stronger degradation of E,th than bT,th

-0.35 cannot be ruled out

Beta scaling depends on plasma shape throughdifference in ELM behavior

Consistent with recent reports from AUG

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Momentum Transport Studies (w/ W. Solomon)

• Low BT (0.35-0.55 T) operation leads to values of ExB up to the MHz range

• These ExB shear values can exceed ITG/TEM growth rates by factors of 5 to 10

• Statistical studies indicate does not scale with i in NSTX

Due to suppression of ITG modes?

What is level of ,neo?

Does scale with e? One dedicated scan indicates so

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Dedicated Perturbative Momentum Confinement Allow Determination of , vpinch

• Use non-resonant n=3 magnetic perturbations to damp plasma rotation; turn nRMP off for plasma spin-up– Use plasma spin-up dynamics

to determine , vpinch

R~1.15 m

R~1.32 m

• Use dL/dt = T – L/ relation to determine instantaneous

• Model spin-up to determine perturbative using

L(t) = * [T – (T-L0/) * exp(-t/)], whereL = Angular momentumT = Torque

L0 = Angular momentum at time of nRMP turn-off

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Use Change of Toroidal Rotation as a Function of Radius to Model , v, pinch

Peeters et al

Fit with finite v,pinch

Fit with v,pinch=0

TRANSP

• Significant inward pinch results

• Expt’l inward pinch not inconsistent with Peeters et al, based on Coriolis effect

= /R [-4-R/Ln]

– <vPeeters> = -11, -49 m/s @ = 0.6, 0.8

– vexptl = -18, -30 m/s

– Effect of off-diagonal terms (Te, ne)?

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Summary

• Degradation of E with T in weakly-shaped plasmas– Degradation invariably tied to change in ELM severity

• Momentum transport studies are just beginning– Steady-state power balance and perturbative analyses indicate long

momentum confinement times (>100 ms), with <<i

– Momentum diffusivity does not scale with ion thermal diffusivity• Possibly due to suppression of ITG modes in NSTX, and neoclassical

transport controlling both ion heat and momentum diffusion

– Strong inward pinch velocity inferred from perturbative analysis• Comparisons to theory underway