Experimental study on the spatial structures of filament during ELM crash in ELMy H-mode discharge on EAST

A high-speed vacuum ultraviolet imaging (VUVI) system with both high temporal and spatial resolutions in the Experimental Advanced Superconducting Tokamak has been developed for the study of the edge/pedestal plasma. Edge localized mode (ELM)-induced filamentary structures have been successfully visualized by the VUVI system during the ELMy high confinement mode (H-mode) discharges. The poloidal mode spacing and the pitch angle are employed to quantitatively characterize the spatial structure of the observed filamentary structures in the imaging data. The poloidal mode spacing of the filamentary structure is found to be proportional to the plasma current. The dominant toroidal mode number decreases as the plasma current ramps up. In addition, the temporal evolution of the pitch angle during an ELM crash was quantitatively investigated. No significant change in the pitch angle is observed during an ELM crash. The dominant toroidal mode number gradually decreases in the rise phase and increases in the decay phase in one ELM crash, respectively.