Gas jet disruption mitigation of locked mode plasmas using DPCS real-time detection and response R. Granetz, D. Whyte, S. Angelini, S. Wolfe DPCS real-time detection of VDEs and subsequent firing of the gas jet worked well. DPCS: no false positives, no misses, fast response Mitigation: good, but not quite as good as with stable plasmas on the midplane. Not surprising, given the short VDE timescale on C-Mod We want to use DPCS to detect and mitigate other kinds of disruptions as well (locked mode, density limit, β-limit, …) Alcator C-Mod Ideas Forum, Dec 2006

Digital Plasma Control System (DPCS) monitors vertical position, fires gas jet

Alcator C-Mod Ideas Forum, Dec 2006 Some details Two options for DPCS: Continuously calculate 2/1 error field from Wolfe’s model[1] and compare to locked mode threshold scaling[2,3]. Trigger when getting ‘close’. Or, use a central ECE channel and look for the cessation of sawteeth (perhaps with some use of the predictive model). Must develop an algorithm and software to get DPCS to recognize ‘cessation of sawteeth’. Neural net? Time response of DPCS and gas system should not be as critical as with VDEs Requires 1 dedicated run, plus piggybacking to test out the DPCS locked mode prediction software. Alcator C-Mod Ideas Forum, Dec 2006