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Stanley M. Kaye Wayne Solomon PPPL, Princeton University ITPA Naka, Japan October 2007

Supported by. Rotation & Momentum Confinement Studies in NSTX. Stanley M. Kaye Wayne Solomon PPPL, Princeton University ITPA Naka, Japan October 2007. High Rotation (M ~0.5) and Rotational Shear Observed in NSTX.

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Stanley M. Kaye Wayne Solomon PPPL, Princeton University ITPA Naka, Japan October 2007

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  1. Supported by Rotation & Momentum Confinement Studies in NSTX Stanley M. Kaye Wayne Solomon PPPL, Princeton University ITPA Naka, Japan October 2007 1

  2. High Rotation (M ~0.5) and Rotational Shear Observed in NSTX • 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 Steady-state and perturbative momentum confinement studies on NSTX have started 2

  3. Local Transport Studies Reveal Sources of Energy Confinement Trends Electrons primarily responsible for strong BT scaling in NSTX (tE~BT0.9) Variation in near-neoclassical ion transport primarily responsible for Ip scaling (tE~Ip0.4) Electrons anomalous Ions near neoclassical Neoclassical Neoclassical levels determined from GTC-Neo: includes finite banana width effects (non-local) 3

  4. Steady-State Momentum Transport Also Can Be Determined From These Scans No anomalous pinch necessary to explain rotation data 4

  5. Core Momentum Diffusivities Up to An Order of Magnitude Lower Than Thermal Diffusivities Is momentum diffusivity tied more to electron diffusivity when ions are neoclassical? 5

  6. Steady-State cfDoes Not Scale With ci As At Conventional Aspect Ratio Due to ITG suppresson? What is cf, neo? Steady-state: from momentum balance (TRANSP) assuming no explicit pinch 6

  7. Momentum Diffusivity NOT Neoclassical Even Though Ion Thermal Diffusivity Is (~) cf,neo << cf cf, neo can be negative! 7

  8. Inward Neoclassical Momentum Flux Driven By Ti Relation to source of intrinsic rotation? 8

  9. Relation of cf and cf to cf,neo Independent of Ion Thermal Diffusivity and Its Relation to Neoclassical Extend analysis to ci>>ci,neo (L-mode) 9

  10. Dedicated Perturbative Momentum Confinement Experiments Recently Carried Out • Use non-resonant n=3 magnetic perturbations to damp plasma rotation • Previously been used to slow plasma rotation for ITER-relevant RWM stabilization experiments (Sabbagh et al.) Observed rotation damping consistent with neoclassical toroidal viscosity (NTV) theory Steady-state & transient application 10

  11. Steady-State Application of n=3 NRMP Confirms Maximum Torque at R>~1.3 m • Delay in start of vf decrease going inwards from ~1.38 m • Beware: 10 ms time resolution Vf at R=132 cm Vfat center IRWM 11

  12. Perturbative tf, cf Can be Obtained from Transient Application of nRMP • No apparent delay in recovery of vf after nRMP braking removed R~1.32 m R~1.15 m 12

  13. Momentum Confinement Time >>Energy Confinement Time in NSTX (Consistent with cf<<ci) • 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 (NB torque only) L0 = Angular momentum at time of nRMP turn-off Steady-state tE ~ 50 ms 13

  14. Perturbative Momentum Transport Studies Using Magnetic Braking Indicate Significant Inward Pinch • Can determine vpinch only if w, w decoupled • Assume cfpert, vpinchpert constant in time • Expt’l inward pinch generally scales with theoretical estimates based on low-k turbulence-driven pinch vPeeters= cf/R [-4-R/Ln] (Coriolis drift) vHahm= cf/R [-3] (B, curvature drifts) • Effect of off-diagonal terms (Te, ne)? • cfs-s < cfpert with inward pinch Important to consider when comparing cf to ci 14

  15. Reasonably Good Agreement Between Theory and Experiment in Limited Comparison Can comparisons with large variations in Ln be used to discriminate between theories? 15

  16. R~1.32 m R~1.15 m Varying Levels of Applied nRMP Can Probe Dynamics and Hysteresis of tf, cf Largest effect again seen for R>~1.3 m 16

  17. Discussion Points • Main conclusions • tf >>tE; cfpert>cfs-s (inward pinch significant) • Inferred vpinch cf, magnitude not inconsistent with theory predictions • Will continue to run experiments over next couple of years to study steady-state and perturbative momentum transport • Long pulse plasmas to study cfs-sitself and effect on energy transport • Multiple perturbations: use n=1 feedback, run at higher BT, lower b to suppress MHD • Apply additional torque in core: modulated beams (beam profile peaked) • Need to understand decoupling of momentum and ion energy transport • Is this because ions are near neoclassical (i.e., ITG modes suppressed)? • Under what conditions would ITG be unstable? • How low does ExB have to be? • Will coupling re-emerge at this point? • Is cf coupled to ce? Need dedicated scans • Is vpinch significant or necessary? • Significant within data uncertainties? • Is cfpert & vpinchpert a better physics description than cfs-s? • Are theories for rotation damping (e.g., NTV) applicable to ITER, CTF? • Can they be used as a basis for prediction? • What do they predict? 17

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