Study on edge localized mode during plasma vertical swing in HL-2A tokamak

An experiment on edge localized modes (ELMs) during the vertical swing is performed in HL-2A tokamak. ELM mitigation is observed when the plasma moves upward. The plasma column expands accompanied by a decrease in both lower triangularity and the absolute value of local magnetic shear at the outer mid-plane during the upward moving. The critical pressure gradient in pedestal is reduced for the mitigating case according to the linear simulation based on peeling-ballooning theory. The physics of the ELM crash process is also explored through nonlinear simulation. For the mitigating case, small current drive for low-n modes and a weak ion diamagnetic effect on high-n modes lead to a higher dominant mode and a wider growth rate spectrum, which result in weak turbulence transport and a small ELM size.