BOUT++ nonlinear simulation for a comparative study with the measured 2D ELM structures in the KSTAR H-mode plasma

Abstract

Time-dependent nonlinear simulation using the BOUT++ 3-field model is performed for a study of edge localized mode (ELM) dynamics in KSTAR H-mode plasmas. The simulated results of the ELM evolution are directly compared with the 2D ELM structures, measured by electron cyclotron emission imaging systems, from the initial growth to crash phase. The simulation results are qualitatively in good agreement with the observations. Specifically, it is notable in simulation and experiment that higher-n modes in a quasi-steady state phase evolve into lower-n modes close to the ELM-crash in time. It suggests that lower-n modes may be responsible for the onset of the crash. A postanalysis supports that nonlinear mode coupling between toroidal harmonics may drive the lower-n mode.