Comparison study of nonlinear simulations and VUVI measurements of filamentary structures during an ELM crash

A time-dependent nonlinear simulation was performed using the BOUT++ 3-field model to study the spatial characteristics of the filamentary structure observed in the EAST H-mode plasmas. The simulation results were qualitatively compared with the experimental images captured by the vacuum ultraviolet imaging system. During the nonlinear evolution period, the poloidal mode spacing increases and the dominant toroidal mode number of the edge localized mode (ELM) decreases with time. In addition, no significant change is observed in the pitch angle. Both the simulation results and experimental measurements show the same time dependence. In addition, it is found that the dominant toroidal mode number during the ELM crash does not decrease continuously with time in the experimental measurements, i.e., the dominant toroidal mode number is higher than that of the previous frame or is lower than that of the next frame during the ELM crash, which can be explained by the hypothesis of nonlinear mode coupling since it can be reproduced by using the output considering the nonlinear mode coupling effect.