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XP 942: ELM Stability Dependence on d

NSTX. Supported by. XP 942: ELM Stability Dependence on d. College W&M Colorado Sch Mines 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 Purdue U SNL Think Tank, Inc. UC Davis

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XP 942: ELM Stability Dependence on d

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  1. NSTX Supported by XP 942: ELM Stability Dependence on d College W&M Colorado Sch Mines 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 Purdue U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin A. Sontag1, J. Manickam2,T. Osborne3, P. Snyder3, R. Maingi1, 1) Oak Ridge National Laboratory 2) Princeton Plasma Physics Laboratory 3) General Atomics 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 JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec

  2. Observed NSTX ELM Stability Not Consistent with ELITE Calculations 1.2 0.8 0.4 0.1 Edge current [(jmax+jsep)/2<j>] 3 4 5 6 7 8 Normalized Pressure Gradient () Dependence of pedestal pressure limit in major radius at fixed minor radius NSTX peeling-ballooning stability as calculated by ELITE for a discharge with Type I ELMs • ELITE indicates NSTX should be P-B stable • ELMs observed even though g/(w*/2) << 1 • nearer to peeling boundary • farther from ballooning boundary • PEST indicates ballooning may be important • Reduced d can increase ballooning instability drive • high-d opens up 2nd stability at low A

  3. Ballooning stability roughly proportional to average d • dupper scanned at fixed dlower • Peak stable bN increases with increasing davg 10 dlower = 0.3 dlower = 0.4 dlower = 0.2 5 bN 0 0 0.25 0.5 dupper

  4. XP Goal: Increase Ballooning Drive with decreased d to Alter ELM Character • Reduce shaping to alter stability curve • Start with low-d ELMy discharge • Type-I (~ 10% DWMHD) • LITER @ 10 mg/min • Vary d upper and lower • push with PF1As time (s) From Snyder, et al., PPCF 46 (2004) A131

  5. Decrease in dlower Changes ELM Character • Use PF1AL and S.P. ramps to push dlower down • Other parameters held constant • Transition to small ELM regime coincident with dlower ramp PF1AL ramp

  6. Detailed Analysis Ongoing • Next: edge equilibrium (bEFIT) and stability (ELITE/PEST) analysis • Good TS data for edge profiles during small-ELM period • More difficult for large-ELM discharges • look through similar shots for good ELM/TS timing

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