Second Switching Power Amplifier (SPA) Upgrade Physics Considerations Discussion S.A. Sabbagh 1, and the NSTX Research Team 1 Department of Applied Physics, Columbia University, New York, NY, USA NSTX ARRA Meeting May 20, 2009 PPPL 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 Sandia NL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin 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 NSTX Supported by v1.0

NSTX Second SPA Upgrade - discussion (S.A. Sabbagh)May 20 th, Second Switching Power Amplifier Planned for NSTX  Part of NSTX 5-year Plan  ( ) “Implement 2 nd switching power amplifier (SPA) to allow independent control of all 6 midplane RWM coils”  Engineering meeting held in parallel to March ReNeW workshop at PPPL  Existing Status (bullets from Raki’s talk 3/18/09)  The Six RWM coils are grouped in pairs  Each Pair is fed from one sub-unit of SPA which has 3 sub-units  Each coil has two turns. Maximum of 3.33kA Pulsed power feed.  Three dedicated ckts. & power loops for RWM Coils exist  Proposed Change  Each RWM coils are to be individually fed  Each coil to be fed from one sub-unit of SPA

NSTX Second SPA Upgrade - discussion (S.A. Sabbagh)May 20 th, Some physics program considerations for 2 nd SPA  More flexible RWM feedback capability  n = 2 (and n = 3) field for rotation control during n = 1 RWM feedback  Could begin multi-mode RWM control studies, n = 2 with n = 1 RWM feedback  Greater spectrum for dynamic error field correction  More flexible rotation control capability  Simultaneous odd/even n field spectrum for NTV rotation control  Greater rotation control flexibility for real-time rotation control  More flexible field generation for ELM control  independent n = 1, 2, 3 amplitude and phase control for RMP studies (with n=1 RWM feedback)  Independent use for CHI  Run CHI absorber and n=1, 3 control simultaneously

NSTX Second SPA Upgrade - discussion (S.A. Sabbagh)May 20 th, Design work for upgraded non-axisymmetric control capabilities has begun  Capabilities  Non-axisymmetric control coil (NCC) – at least four applications RWM stabilization (n > 1, higher  N ) DEFC with greater field correction capability ELM control (n = 6) n > 1 propagation, increased V  control) Similar to proposed ITER coil design Consider design to allow moderate 3-d shaping for mode control In incremental budget  Addition of 2 nd SPA power supply unit for simultaneous n > 1 fields  Non-magnetic RWM sensors; advanced RWM active feedback control algorithms Primary PP option Secondary PP option Existing coils Proposed Internal Non-axisymmetric Control Coil (NCC) (initial designs - 12 coils toroidally) RWM with n > 1 RWM observed (Sabbagh, et al., Nucl. Fusion 46, 635 (2006). )

NSTX Second SPA Upgrade - discussion (S.A. Sabbagh)May 20 th, VALEN RWM predictions for new control coils behind passive plates (PP) coils behind copper passive plates perform worse than existing external RWM change copper passive plates to SS RWM performs better than existing external RWM nn growth rate  [1/s] passive Ideal wall limit copper PP Coils behind Cu secondary PP Coils behind Cu primary PP external system nn growth rate  [1/s] passive Ideal wall limit partial steel PP Coils behind SS secondary PP Coils behind SS primary PP external system J. Bialek

NSTX Second SPA Upgrade - discussion (S.A. Sabbagh)May 20 th, Proposed NSTX upgrade, coils on plasma side of passive plates Possible upgrades: coils on plasma side of passive plates we examine only one such coil system at a time we approach the ideal wall limit with either coil system new coils plasma side primary passive plates new coils plasma side secondary passive plates

NSTX Second SPA Upgrade - discussion (S.A. Sabbagh)May 20 th, New control coils on plasma side of NSTX copper passive plates (PP) stabilize to C  >99% passive existing coils Ideal wall limit existing coils nn nn growth rate  [1/s] coils on plasma side Cu secondary PP stabilize to  n = 7.04 coils on plasma side Cu primary PP stabilize to  n = 7.05 Ideal wall limit  n = 7.06 J. Bialek

NSTX Second SPA Upgrade - discussion (S.A. Sabbagh)May 20 th, Recent ELM mitigation results show promising results with NCC  n = 6 configuration  Higher q 95 shows best results T. Evans, GA

NSTX Second SPA Upgrade - discussion (S.A. Sabbagh)May 20 th, Consider a more capable power supply upgrade to best support future non-axisymmetric field upgrades?  Investment to support future upgrades  JEM: “2nd SPA would be needed for any future RMP/RWM/EF control coils, so this is a good investment”  JEM: “More coils are next in line as a possible major facility upgrade”  Consider a power supply that will best support internal NCC coil upgrade  Internal RWM coil upgrade will allow expanded physics studies that is best supported by faster power supplies  RWM stabilization up to the with-wall beta limit (  growth < 1 ms)  Greater control capability for RWMs with fast growth (  growth < 1 ms)  Potential for control of NTMs at large R (f ~ n*10 kHz)  Potential for non-resonant increase of plasma rotation (f ~ n*10 kHz)