Beta Scaling and Momentum Transport Studies XPs 713 & 723

1. Office of Science Supported by Beta Scaling and Momentum Transport StudiesXPs 713 & 723 College W&M Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAERI Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec S.M. Kaye NSTX Results Review July 23-24, 2007 PPPL, Princeton University 1

2. XPs Performed to Study Different Transport Properties in NSTX • XP713 Beta Scaling • High priority ITPA task – important to success of ITER AT scenario • Follow on from last year’s beta scaling results • Power scan at k=2.1, d=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 • XP723 Momentum Transport Studies (w/W. Solomon) • Statistical studies show cfand ci 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 cf from vpinch 2

3. Dimensionless Parameter Scans Have Addressed High-Priority ITPA Issues – Beta Dependence of Confinement b-scan at fixed q, BT - b-dependence important to ITER advanced scenarios (Bt98y2~b-0.9) - Factor of 2-2.5 variation in bT - Degradation of tE with b weak on NSTX Test shape dependence with similar power scan - k=1.8-1.9, d~0.4 - ne*, re vary ≤ 20% across scan - ELM severity increased with increasing power • Only few % loss per ELM • High frequency ELMs at low power (Type III?) 20% variation in re, ne* k=2.1 d=0.6 3

4. Observed Weak Increase of Beta With Power Strong degradation of tE (tE ~ bT-1.0) Type III ELMs severely degrade confinement Stronger degradation of tE,th than bT,th-0.35 cannot be ruled out Beta scaling depends on plasma shape through difference in ELM behavior Consistent with recent reports from AUG 4

5. Momentum Transport Studies (w/ W. Solomon) • Low BT (0.35-0.55 T) operation leads to values of wExB up to the MHz range • These ExB shear values can exceed ITG/TEM growth rates by factors of 5 to 10 • Statistical studies indicate cf does not scale with ci in NSTX Due to suppression of ITG modes? What is level of cf,neo? Does cf scale with ce? One dedicated scan indicates so 5

6. R~1.32 m R~1.15 m Dedicated Perturbative Momentum Confinement Allow Determination of tf, cf, vpinch • Use dL/dt = T – L/tf relation to determine instantaneous tf • Model spin-up to determine perturbative tf using L(t) = tf* [T – (T-L0/tf) * exp(-t/tf)], where L = Angular momentum T = Torque L0 = Angular momentum at time of nRMP turn-off • 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 tf, cf, vpinch 6

7. Use Change of Toroidal Rotation as a Function of Radius to Model cf, vf, pinch Fit with finite vf,pinch • Significant inward pinch results • Expt’l inward pinch not inconsistent with Peeters et al, based on Coriolis effect = cf/R [-4-R/Ln] • <vPeeters> = -11, -49 m/s @ r= 0.6, 0.8 • vexptl = -18, -30 m/s • Effect of off-diagonal terms (Te, ne)? Fit with vf,pinch=0 TRANSP Peeters et al 7

8. Summary • Degradation of tE with bT 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 cf<<ci • 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 8