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XP802: Active RWM stabilization system optimization and ITER support

XP802: Active RWM stabilization system optimization and ITER support. Goals Alter active control configuration to achieve highly reliable RWM stabilization at various plasma rotation, w f Upper/lower RWM B r , B p sensors, follow from best CY2007 feedback settings

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XP802: Active RWM stabilization system optimization and ITER support

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  1. XP802: Active RWM stabilization system optimization and ITER support • Goals • Alter active control configuration to achieve highly reliable RWM stabilization at various plasma rotation, wf • Upper/lower RWM Br, Bp sensors, follow from best CY2007 feedback settings • Br sensor feedback provides RFA correction, Bp provide RWM stabilization • Determine if stable, low wf < w*i operation exists with feedback turned off • If achieved, control system open as a tool for all NSTX XPs as desired • Specific ITER support requests • Study effect of applied time delay on feedback (requires control system time delay capability) • Determine impact of a large toroidal gap on active RWM stabilization to simulate ITER port plug coil geometry (take out one of six control coils) • Addresses • Joule milestone, ITER Organization (IO) request, NSTX PAC request • ITPA experiment MDC-2 Progress 4/11/08

  2. 2 1 1 1 Initial RWM signature leads to rotating global kink • Transition to global kink indicates that mode is an RWM zoomed view n = 1 feedback on off bN bN RFA DBpn=1 RFA reduced DBpn=1 fBpn=1 DBrmidn=1 DBn=odd DBn=odd

  3. 1 USXR shows transition from RWM to global kink edge • Initial RWM locked signature spins up, amplitude dies away core edge K. Tritz

  4. Tearing mode appears significantly after global kink RWM + 20 ms + 30 ms • Significantly different than DIII-D results (H. Reimerdes) edge core + 50 ms + 40 ms edge core K. Tritz

  5. 2 Terminating event appears to be an internal kink • n = 1 LMD shows mode lock (RWM?) preceding/concurrent w/kink • Internal kink precedes H-L back-transition edge Zoomed in view core edge K. Tritz

  6. n = 1 feedback / RWM results show stabilization detail • General conclusions (so far) • n = 1 feedback system has produced far greater reliability of discharge avoiding RWM • Statistics being compiled • n = 1 feedback system does not insure stability against RWM • Reasons for failure being analyzed (e.g. fast mode growth) • Mode characteristics appear to be RWM, not tearing • Unlike present observation/conclusion by DIII-D • Mode spin up, converts to global kink mode initially, tearing appears later • Feedback system might be easing transition to rotating kink by altering boundary condition • Results to date question the validity of a “critical rotation” for RWM • Next Steps • Analysis of XP830 RWM Stabilization Physics (Berkery), and related analysis to test kinetic stabilization model producing “bands” of stability/instability in rotation, beta

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