Two-dimensional imaging of edge-localized filaments in KSTAR \textit{H}-mode plasmas

The temporal evolution of edge-localized modes (ELM) has been studied using a 2-D electron cyclotron emission imaging (ECEI) system in KSTAR.\footnote{G. S. Yun \emph{et al.}, Phys. Rev. Lett. \textbf{107}, 045004 (2011).} The ELMs are observed to evolve in three distinctive stages: initial linear growth of multiple filamentary structures having a net poloidal velocity, interim saturated state, and final crash. The crash phase, typically consisting of multiple bursts of a single filament, involves a complex dynamics; an abrupt change in the poloidal mode number, poloidal elongation of the bursting filament, development of a fingerlike bulge, and fast localized burst through the finger. A significant alteration of the ELM dynamics, such as mode number, poloidal flows, and crash time scale, has been revealed during a recent investigation of external magnetic perturbations ($n=1$) on ELMs.