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S. A. Sabbagh, T. Evans, D. Gates, R. Maingi, J.E. Menard, J.K. Park, many others…

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, T. Evans, D. Gates, R. Maingi, J.E. Menard, J.K. Park, many others…

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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 Joint Experiment on ELM Mitigation with Midplane Control Coils S. A. Sabbagh, T. Evans, D. Gates, R. Maingi, J.E. Menard, J.K. Park, many others… Joint ELM Mitigation XP Meeting February 4, 2008 Princeton Plasma Physics Laboratory V1.0

  2. Considerations for Joint ELM Mitigation XP Run Plan • Target Plasmas and General Approaches • What target(s) should be used? • Giant ELMs, or smaller ELMs? • What variation of q95? • What plasma shape, DRSEP, etc. ? • DC applied fields • Decide on “most favorable” approaches (see strawman run plan) • AC applied fields • Still examining effect ELMs, connection to toroidal rotation (SAS) • n = 1 feedback – use Br feedback on ELMs with frequency < 1kHz • Technical Logistics of the Run Plan • Application of non-standard DC fields will require overnight buswork change • Group similar needs on same day, put special needs on 0.5 day with another XP not needing RWM coil current • Iterate run plan, review XP by 2/11/08

  3. Joint ELM Mitigation XP - Run plan (STRAWMAN) Task Number of Shots 1) Create targets (i) below, but near and (ii) above ideal no-wall beta limit (control shots) (use 125271 (large ELMs) as setup shot, 2 or 3 NBI sources, relatively high k ~ 2.0 or above to avoid strong rotating modes) A) No non-axisymmetric field, 2-3 NBI sources, q95 ~ 8 2 B) Reduce q95 ~ 6 (NOTE: attempt lower q95 than this?) 2 2) Attempt ELM mitigation with DC fields A) n = 2 + 3 fields 6 B) n = 2 fields, change phasing, amplitude 4 C) n = 3 fields, change amplitude (change NBI torque???) 4 D) n = 6 fields by producing primary n = 0 field 2 E) Try n = 1 (???); change NBI torque (???) 4 3) Attempt ELM mitigation with AC fields A) pre-programmed, match ELM frequency, not-propagating ( 20 < f(Hz) < 800) 2 B) pre-programmed, match ELM frequency, co-propagating ( 20 < f(Hz) < 800) 2 B) pre-programmed, match ELM frequency, counter-propagating ( 20 < f(Hz) < 800) 2 C) n = 1 Br feedback, vary (i) gain (ii) phase 8 4) Additional scans Total 38 V1.0

  4. Extra Slides

  5. Exploratory approach to finding ELM mitigation solution with midplane non-axisymmetric coils • Goal • Demonstration of ELM mitigation with NSTX midplane RWM coil set • Approach (complementary to other proposed plans) • Application of broader n spectrum of DC fields • Non-standard coil configs: (i) turn off one coil, (ii) turn off 5 coils, (iii) turn off every other coil, (iv) slow pre-programmed toroidal propagation of setup (iii) • New “n = 2” applied field capability for 2008, vary phase • Perturbations away from “n = 1” control currents (which have n = 1,5 dominant), superposition of n = 1 – 3, higher n • Bonus: Can get NTV rotation braking data piggyback! • Application of AC fields • Pre-programmed toroidal propagation of several DC setups mentioned above • Might stimulate ELM to allow to transform large ELMs into smaller (acceptable) ELMs • Now examining existing ELM mitigation evidence from past RWM, NTV experiments • N = 1 feedback • Can best feedback configuration from 2007 alter ELM dynamics? • Take best approach above and run in closest ITER shape w/ELMS

  6. Direction of applied n=1 traveling wave alters RWM stability • Stronger RFA with co-flow field • RWM not destabilized Field propagates with flow Field propagates against flow (co-flow) (counter-flow) 80 60 40 20 0 RWM Bp n=1(G) Larger RFA smaller RFA Phase Bp n=1 360 240 120 0 1 0.5 0 -0.5 -1 IRWM(kA) 116940 116941 0.25 0.35 0.45 0.55 Time (s) 0.25 0.35 0.45 0.55 Time (s) • Weaker RFA with counter-flow field • Unstable RWM

  7. 40 30 20 10 0 Ft (kHz) 116941 116940 0.9 1.1 1.3 1.5 R (m) 0.9 1.1 1.3 1.5 R (m) Unstable RWM avoided with rapidly rotating n = 1 • Applied field in the direction of plasma flow: • RFA increases and rotation damps • n=1 internal mode triggered • Rigid rotor rotation profile; beta recovers • Applied field against the plasma flow: • RWM grows • Rapid, complete rotation and beta collapse (applied field co-flow) (counter-flow) co- bNno-wall (DCON) counter core rotation counter co- co- counter 0.0 0.2 0.4 0.6 0.8 Time (s)

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