NSTX 12 th ITPA MHD Meeting 10-2008 – S.A. Sabbagh/S.P. Gerhardt 1 Halo Current and Current Quench Rate Characteristics During Disruptions in NSTX S.A. Sabbagh 1 / S.P. Gerhardt 2 1 Department of Applied Physics, Columbia University, New York, NY, USA 2 Plasma Physics Laboratory, Princeton University, Princeton, NJ, USA For the NSTX Macroscopic Stability Topical Science Group 12th Meeting of the ITPA MHD Stability Topical Group October 20-22, 2008 CRPP, Lausanne, Switzerland 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 JAEA 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 v1.4
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NSTX 12 th ITPA MHD Meeting 10-2008 – S.A. Sabbagh/S.P. Gerhardt 1 Halo Current and Current Quench Rate Characteristics During Disruptions in NSTX S.A.
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Examining disruption eddy currents, halo currents, and Ip current quench in the spherical torus
Goals Provide electromagnetic loading data for future ST design Examine ST specific characteristics to enhance tokamak knowledge base
Considerations High elongation more subject to n = 0 instability during vertical motion (VDE)
• General issue: disruption IP quench drives eddy currents (IC) in nearby conducting structures (C); currents lead to significant JxB forces on in-vessel components
c (LC/RC time) long: total flux change matters
c short: instantaneous flux change matters
• Strong 1/R Bt variation in ST makes center column halo currents a large concern
Halo currents can flow linking the plasma and in-vessel components when plasma comes in contact with plasma facing components
• Currents are parallel to B in the plasma edge; distributed to vessel based on inductance/resistance
Disruptions are faster in the ST vs. conventional aspect ratio
• Expand studies to wider range of disruption conditions/plasma parameters
Mitigation by CT injection may have a number of advantages
The injected compact torus (CT) moves quickly Slowest step in CT mitigation is gas-puffing into the
injector (~200 s). Bias flux can be provided by permanent magnet
By coordinating MGI and CT timing, core cooling could be precisely controlled
The CT species and velocity can be varied to tailor the penetration depth
Could reduce the total amount of injected gas from the MGI system, making recovery easier
It might also allow for tailoring the shut-down to avoid the “hot-tail” runaways which are common with pellets
Further advantages if the CT system is operated in a Marshall Gun mode? A long trailing plasma containing significant neutrals and at amounts >100 times more
than the mass of a single CT can be injected These neutrals would have much higher velocity than what is possible by MGI alone