2D/3D electron temperature fluctuations near explosive MHD instabilities accompanied by minor and major disruptions

Abstract

Minor and major disruptions by explosive MHD instabilities were observed with the novel quasi 3D electron cyclotron emission imaging (ECEI) system in the KSTAR plasma. The fine electron temperature (T-e) fluctuation images revealed two types of minor disruptions: a small minor disruption is a q similar to 2 localized fast transport event due to a single m/n = 2/1 magnetic island growth, while a large minor disruption is partial collapse of the q <= 2 region with two successive fast heat transport events by the correlated m/n = 2/1 and m/n = 1/1 instabilities. The m/n = 2/1 magnetic island growth during the minor disruption is normally limited below the saturation width. However, as the additional interchange-like perturbation grows near the inner separatrix of the 2/1 island, the 2/1 island can expand beyond the limit through coupling with the cold bubble formed by the interchange-like perturbation.