Experimental and simulation studies on ELM characteristics under a plasma current ramping up discharge on EAST

Abstract

Previous experimental results show that the poloidal mode spacing of the filamentary structures increases and the dominant toroidal mode number decreases in the edgelocalized mode (ELM) rising phase with increasing plasma current. In addition, the experimental results in this paper show that the energy loss ratio of the pedestal (ΔW/Wped) decreases as the edge safety factor (q95) increases. The BOUT++ three-field two-fluid model can reproduce the experimental results and provide a possible explanation mechanism. The pedestal density plays an important role in the characteristics of filamentary structures as the current ramps up. On the one hand, the resistivity related to the pedestal density drives the instability of the peeling–ballooning mode, and the resistive effect is stronger in the high current case, making the dominant toroidal mode number lower and the corresponding poloidal mode spacing wider in the high current case. A low q95 corresponds to a high pedestal collision rate and a high pedestal energy loss ratio. On the other hand, the ELM crash process is dominated by resistivity, so the ratio of pedestal energy loss caused by ELM is not inversely proportional to the pedestal collision rate.