Experimental study of ELM-induced filament structures using the VUV imaging system on EAST

A high-speed vacuum ultraviolet (VUV) imaging system has been developed on the Experimental Advanced Superconducting Tokamak (EAST), which selectively measures line emission with a central wavelength of 13.5 nm (CVI, n = 4–2). It has been employed to study edge/pedestal plasma behavior in EAST. Edge localized mode (ELM)-induced filament structures have been captured by the VUV imaging system during the ELMy high confinement mode discharge with both high temporal and spatial resolutions. The typical features (i.e. poloidal width and pitch angle) of the observed filaments are quantitatively characterized based on the VUV imaging data, and the dependence of these features on basic plasma parameters is analyzed. It is found that the poloidal width is proportional to the heating power, and the pitch angle is inversely proportional to the edge safety factor q ₉₅. The scatterplot shows a positive trend between the poloidal width and the ELM amplitude defined by the relative change in stored energy. These results are based on the condition that the perturbation induced by ELMs is confined to a narrow layer in the plasma.