NSTX 2007 MHD XP Review – J. Menard 1 Optimization of RFA detection algorithms during dynamic error field correction Presented by: J.E. Menard, PPPL Final review of XP-702 from MHD task group May 2, 2007 Princeton Plasma Physics Laboratory Supported by Office of Science 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 JAERI Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec 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 SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin

NSTX 2007 MHD XP Review – J. Menard 2 Combination of TF error field correction and n=1 feedback driven by B P sensors optimized plasma performance No error field control during high  N phase TF-EFC TF-EFC + active n=1 B P feedback No-wall limit Rotating mode onset Mode detection –Linear compensation: PF, TF, OH –Assume n=1 thru 2 modes present RWM/EF coil current driven by: –Pre-programmed (braking, spectr.) –Correction of OHxTF EF –Feedback on n=1 component of B P Feedback control optimization: –Scan phase of n=1 B P wrt coil B R –Scan proportional gain (0.7 optimal) B P sensor B R sensor RWM/EF control coil Passive plate

NSTX 2007 MHD XP Review – J. Menard 3 Feedback alone did not suppress  N,   collapses from TF EF Can DEFC be robustly achieved with feedback alone? Robust correction required “good guess” from OHxTF model –Limited by B P mode-ID signal to noise? – desire higher gain? –Limited by mode-ID polarization? - is B R better for EF detection? Optimal phase for RWM control changed when n=3 was eliminated from detection spectrum… –Likely result of missing data due to dead sensors… DEFC feedback assumed only n=1 and n=2 were present –Can this be improved? –Answer is likely yes – with appropriate averaging Experiment: try mixtures of upper, lower, and polarization –Try B R for EF detection and control –Also try upper/lower averaging of sensor signals –Also try mixture of B R and B P – best for EF and RWM control?

NSTX 2007 MHD XP Review – J. Menard 4 Up/down average of poloidal array signals can improve mode-ID sensitivity when sensors are dead/missing Peak / baseline = 5 Peak / baseline = 8-10 Upper array was commonly used for RWM and EF feedback Lower better - only when most sensors were working (which wasn’t the case) Peak / baseline = Up/down average maximizes mode amplitude / baseline  higher G P possible?

NSTX 2007 MHD XP Review – J. Menard 5 Up/down averaging phase-shift scans indicate  is optimal for isolating n=1 B P of mode (assumed pure n=1)

NSTX 2007 MHD XP Review – J. Menard 6 Up/down averaging phase-shift scans indicate 240  & 320  optimizes isolation of n=1 B R of mode (assumed pure n=1)

NSTX 2007 MHD XP Review – J. Menard 7 Shot plan for 1 run day If intrinsic error field is too small to produce measurable RFA, apply pre- programmed n=1 field to generate RFA and loss of RWM stabilization  Goal would be to have DEFC correction system null applied currents!  Perhaps we should apply n=1 (larger than EF) no matter what? Document RFA suppression by DEFC using BP-U only (no OHxTF) –Scan feedback phase and gain to minimize RFA & rotation damping (8 shots) Use up/down average of BP (no OHxTF) –Scan feedback phase and gain to minimize RFA & rotation damping –Is stable gain higher? Is RFA suppression larger? (6 shots) (this case should have similar gain as BP-U only…) Use up/down average of B R (no OHxTF) –Scan feedback phase and gain to minimize RFA & rotation damping (8 shots) Use mixed up/down average of B R + up/down average of B P –Scan feedback phase and gain to minimize RFA & rotation damping (8 shots)