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Gyrokinetic Calculations of Microturbulence and Transport for NSTX and Alcator C-MOD H-modes

Gyrokinetic Calculations of Microturbulence and Transport for NSTX and Alcator C-MOD H-modes. Martha Redi Princeton Plasma Physics Laboratory NSTX Physics Meeting March 17, 2003 Princeton Plasma Physics Laboratory Acknowledgement: R. Bell, D. Gates, K. Hill, S. Kaye, B. LeBlanc, J. Menard,

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Gyrokinetic Calculations of Microturbulence and Transport for NSTX and Alcator C-MOD H-modes

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  1. Gyrokinetic Calculations of Microturbulence and Transport for NSTX and Alcator C-MOD H-modes Martha Redi Princeton Plasma Physics Laboratory NSTX Physics Meeting March 17, 2003 Princeton Plasma Physics Laboratory Acknowledgement: R. Bell, D. Gates, K. Hill, S. Kaye, B. LeBlanc, J. Menard, D. R. Mikkelsen, G. Rewoldt (PPPL), C. Fiore, P. Bonoli, D. Ernst, J. Rice, S. Wukitch (MIT) W. Dorland (U. Maryland) J. Candy, R. Waltz (General Atomics) C. Bourdelle (Association Euratom-CEA, France)

  2. Motivation - Investigate microinstabilities in NSTX and CMOD H-mode plasmas exhibiting unusual plasma transport - High ce, low ci, resilient Te profiles on NSTX; ITB formation on CMOD - Identify underlying key plasma parameters for control of plasma performance METHOD - GS2 and GYRO flux tube simulations - Complete electron dynamics. 3 radii, 4 species. - Linear electromagnetic; nonlinear, electrostatic calculations (CMOD) RESULTS: - Gyrokinetics connection with transport: Questions remaining on NSTX Consistent with transportanalysis on CMOD

  3. GS2 criterion H-mode plasmas: • GS2: Linear, fully electromagnetic, 4 species • Criteria: r/L<<1 for GS2, • but profile effects can mix different wavelengths • => r* stabilization (GYRO) • NSTX zone, rho-star, # ion gyroradii across plasma • 0.25r/a r*=0.0185/0.6= 0.031 32 • 0.65r/a 0.014 71 • 0.80r/a 0.0064 157 • CMOD • 0.25r/a 0.008 122 • 0.45r/a 0.008 122 • 0.65r/a 0.006 167

  4. NSTX: NBI in MHD Quiescent Discharge: Ti> Te, Resilient Te Profiles 108730 Ip = 0.8 MA BT = 0.5 T PNBI = 4 MW ENBI= 90 keV bT = 16% W = 0.23 MJ LeBlanc-APS-02

  5. Two Distinct Plasma Conditions: Resilient Te Profiles during Flattop Period Overlay of 8 consecutive time points: 0.38 - 0. 49 s. Overlay of 11 consecutive time points: 0.53 - 0.69 s. LeBlanc-APS-02 Shoulders at 65 and 125 cm disappear during the later phase

  6. NSTX H-mode: Electron Temperature Profile Resiliency During H-mode Te(r) remains resilient electron density increases ion temperature decreases What clamps Electron temperature profile? Examine microinstability Growth rates at 3 zones

  7. Gyrokinetic Model Equations Perturbed electrostatic potential: Linearized gyrokinetic equation in the ballooning representation, Using the “s-a” model MHD equilibrium: Where Kotschenreuther, et al Comp. Phys. Comm. 88, 128 (1995)

  8. GS2 Evolution of Linear Growth Rates for kI = 0.1 to 0.8 Some stable, some unstable

  9. NSTX r/a=0.8: ITG Range of Frequencies

  10. NSTX r/a=0.8: ETG Range of Frequencies

  11. NSTX r/a=0.65: ITG Range of Frequencies

  12. NSTX Core: ITG Range of Frequencies

  13. NSTX: Examine Microinstability Growth Rates at 3 Zones

  14. Experimental Ti < ITG Critical Gradient r/a=0.25 RTi/Ti < RcTi/Ti r/a=0.65 RTi/Ti ~ RcTi/Ti r/a=0.80 RTi/Ti < RcTi/Ti • Stable ITG drift modes are consistent with the Kotschenreuther Criterion

  15. NSTX: Critical Gradient Below or At Marginal Stability for ITG

  16. NSTX:Above Critical Gradient for ETG Modes

  17. Summary: Comparison of NSTX H-modeTransport Coefficients to Gyrokinetic Stability Why is ce so large and ci so small? Does ETG maintain resilient Te profiles?Need nonlinear and global calculations; MSE and fluctuation diagnostics ci ce ITG ETG r/a >>ci 0.25 t=0.4s t=0.6s >>ci t=0.4s t=0.6s 0.65 >>ci t=0.4s t=0.6s 0.80

  18. Trigger: CMOD Internal Transport BarrierExamine Microinstability Growth Rates at 3 Zones Ne Te Ni(deut) Ti

  19. CMOD -Microturbulent Eigenfunctions: Ballooning Structure along field line Real and imaginary Parts of electrostatic Eigenfunction outside ITB region ki=0.1 to 0.8 Highest growth rates at 0.4-0.5 “Classic” Ion Temperature Gradient Drift Mode

  20. ITB Trigger Time:Linear, Electromagnetic Gyrokinetic Calculations with GS2:Drift wave Microturbulence at ki = 0.1 to 80.Low kI: ITG => Ianomalousoutside ITB TEM and ITG: already stabilized at and within ITBHigh ki: ETG driven by strong Te => eanomalousat and outside ITB Ion drift direction Electron drift direction

  21. NONLINEAR GS2 Simulations confirm linear resultsITB TRIGGER: Before ne peaks, region of reduced transport and stable ITG microturbulence is established without ExB shear Quiescent, microturbulence in ITB region Moderate microturbulence in plasma core High microturbulence level outside half-radius Outside ITB In plasma core Just inside ITB 2  dV • Strongest driving force: • grad Te/Te

  22. Heat Pulse Propagation(Wukitch, Phys. Plas 9 (2002) 2149) Sawtooth heat pulse propagation measurements of similar experiments: Effective heatpulse reduced (by factor~10) in a narrow radial region of ~1 cm, located near the foot of the particle barrier, not necessarily within the barrier GS2 =>c drops to neoclassical in core and by 1/2 at the barrier

  23. TRANSP analysis indicates barrier in eff (r,t) persists after density rise is arrested (1.25 - 1.45 sec)ITB phase has been “controlled” eff = (ne Te e + ni Ti i)  (ne Te + ni Ti ) Bonoli, APS 2001

  24. CMOD H-mode GS2 Results • ITB TRIGGER: Before ne peaks, region of reduced transport and • stable microturbulence is established • without ExB shear • ITG, toroidal ion temperature gradient mode => Ianomalous, unstable outside ITB stabilized at & within the ITB, e drops within ITB At ITB, stabilized by steep density profile and moderate Te • ETG at higher values of kI => eanomalousoutside and at ITB • Primary contribution to cD: from small values of kI, long l Expect neoclassical e, i in core, as found with TRANSP • Nonlinear simulations confirm quiescent microturbulence at ITB Sensitivity studies => ITB observed with off-axis but not on-axis RF is due to weaker (Te)/Te at the barrier, low q(r), 3% Boron ITB also occurs spontaneously in ohmic H-mode, Full story will require detailed comparative study of experiments. Need: Ti(r) and reflectometry fluctuation measurements at ITB

  25. SUMMARY: GS2 linear calculations of drift wave instabilities in the ion temperature gradient and electron temperature gradient range of frequencies, and ExB shear rate: Roughly consistent with improved ion confinement in NSTX and improved confinement within and at ITB in CMOD H-mode plasmas Remarkably good ion transport in NSTX H-mode (Gates, PoP 2002) would be expected from stable ITG throughout plasma Profile effects (GYRO) via r* stabilization may stabilize ITG everywhere. Electron transport => q monotonic so unstable ETG at all r…need MSE Resilient temperature profiles on NSTX may be maintained through ETG instabilities, Nonlinear calculations needed. Tearing parity microturbulence found - in contrast to tokamaks - effects on transport to be determined. Internal transport Barrier on CMOD appears after off-axis RF heating, where microstabilities are quiescent. Nonlinear calculations in ~ agreement with linear. Sawtooth propagation measurements confirm low transport in the region at the trigger time (Wukitch, PoP, 2002).

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