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S.A. Sabbagh, J.M. Bialek, S.P. Gerhardt, R.E. Bell, J.W. Berkery, B. LeBlanc, J.E. Menard, et al.

Supported by. Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics NYU ORNL PPPL PSI SNL UC Davis UC Irvine UCLA UCSD U Maryland U New Mexico U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U

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S.A. Sabbagh, J.M. Bialek, S.P. Gerhardt, R.E. Bell, J.W. Berkery, B. LeBlanc, J.E. Menard, et al.

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  1. Supported by Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics NYU ORNL PPPL PSI SNL UC Davis UC Irvine UCLA UCSD U Maryland U New Mexico U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U Niigata U Tsukuba U U Tokyo JAERI Ioffe Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching U Quebec XP1023:Optimized RWM control for high <bN>pulseat low collisionality and li S.A. Sabbagh, J.M. Bialek, S.P. Gerhardt, R.E. Bell, J.W. Berkery, B. LeBlanc, J.E. Menard, et al. Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA Princeton Plasma Physics Laboratory NSTX Physics Meeting April 26th, 2010 Princeton Plasma Physics Laboratory V1.0

  2. XP1023:Optimized RWM feedback control for high <bN>pulseat low collisionality and li • Motivation • Next-step ST devices (including the planned upgrade of NSTX) aim to operate at plasma collisionality and li below usual NSTX levels • 2009 XP948 showed significantly higher RWM activity, lower bN limit, in reduced li plasmas (li ~ 0.45 and below) • Overall Goal • Improve reliability of RWM stabilization at low li, understand impact of reduced plasma collisionality using new LLD capability • Progress • Generated reduced li target plasmas • Generated unstable RWMs without manipulating plasma rotation • Utilized new bN feedback, new RWM control algorithms • Insufficient tE to complete XP, but developed target for XP1020

  3. bN/li ARIES ST (DEMO) 13 12 11 10 ST-CTF bN NSTX database DCON bNno-wall XP948 Uncontrolled RWM Stable / controlled RWM li NSTX XP948 operated very low li, with high probability of RWM – can these plasmas be better controlled? • Advancement in bN/li toward targets • 2006 value: 11 • XP948 (2009): 13 • ST-CTF: 16 • Uncontrolled growing RWM occurred in about 50% of shots • ST-CTF target must be sustained indefinitely • What value of li is the current-driven kink limit (unstable any b)? • DCON n = 1 no-wall limit for 135111 low: bN = 2.8 (li = 0.38) XP948: S.P. Gerhardt

  4. XP1023: unstable RWM created in low li target plasma • Clear unstable RWMs produced • Although tE was low, unstable RWM generated without n = 3 braking 137722 unstable RWM RWM rotation

  5. XP1023: new low li targets generated with reduced n = 1 ideal no-wall beta limit • Ip = 1.0 and 1.1 MA target plasmas • No-wall beta limit significantly reduced • Ip = 1.1MA target: DCON n = 1 no-wall limit low for 137722: bN < 2.8 (li ~ 0.4) • With single LITER, this target was not reliably reproduced last Thursday to use in XP1020 bN/li ARIES ST (DEMO) 13 12 11 10 “usual” n = 1 bNno-wall limit ST-CTF bN Reduced bNno-wall < 2.8 Filled = over the no-wall limit (Ip = 1.1 MA) li

  6. XP1023: new low li targets generated with reduced n = 1 ideal no-wall beta limit • Ip = 1.0 and 1.1 MA target plasmas • No-wall beta limit significantly reduced • Ip = 1.1MA target: DCON n = 1 no-wall limit low for 137722: bN < 2.8 (li ~ 0.4) • Ip = 1.0MA target: DCON n = 1 no-wall limit low for 137804: bN = 3.4 (li ~ 0.5) • Unstable RWM without n = 3 braking • Ip = 1.0 target was reliable: moved on and used it in XP1020 bN/li ARIES ST (DEMO) 13 12 11 10 “usual” n = 1 bNno-wall limit ST-CTF bN Ip = 1.0 MA bNno-wall = 3.4 Ip = 1.1 MA bNno-wall < 2.8 Filled = over the no-wall limit li

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