Model of ELM suppression by RMPs in DIII-D

Tokamak FMR theory [9] has been used to describe and quantify physical processes involved in various stages of RMP effects and an ELM crash response that lead to bifurcation into an ELM-suppressed state: 1) in the ELMing equilibrium, flow screening is strong with little magnetic reconnection; 2) the RMP at q = 8=2 penetrates via FMR induced by the ELM crash which locks the toroidal flow to the lab frame (like error field mode locking); 3) the ELM crash provides a 8/2 seed island (like NTMs) governed by the MRE; 4) then, if the total 8/2 RMP is large enough, the internal tearing-type (magnetic island) response and flow bifurcate; and 5) flutter transport significantly reduces pedestal top gradients, stabilizing P-B modes and thereby suppressing ELMs. This analysis is for discharge 158115 in DIII-D [1, 2]. More work is required to determine how universal this ELM-crash-induced ELM suppression scenario is and its potential utility in defining criteria for achieving ELM suppression with RMPs in ITER.