Two-Dimensional Visualization of Growth and Burst of the Edge-Localized Filaments in KSTAR $H$-Mode Plasmas

The filamentary nature and dynamics of edge-localized modes (ELMs) in the KSTAR high-confinement mode plasmas have been visualized in 2D via electron cyclotron emission imaging. The ELM filaments rotating with a net poloidal velocity are observed to evolve in three distinctive stages: initial linear growth, interim quasisteady state, and final crash. The crash is initiated by a narrow fingerlike perturbation growing radially from a poloidally elongated filament. The filament bursts through this finger, leading to fast and collective heat convection from the edge region into the scrape-off layer, i.e., ELM crash.

Figure 1

(a) Time evolution of $D_{\alpha }$ emission, core and edge ECEI signals, and $n_{e,l}$ for ELMy $H$-mode plasma (shot no. 4362). (b) ECEI snapshot showing the core $m/n=1/1$ internal kink (left) and the edge filaments (right). The cross marks are the approximate positions of the two ECEI channels. The middle figure depicts EFIT reconstructed flux surfaces overlaid on top of a fast visible camera image. The directions of $B_0$ and $I_p$ are both out of the plane.

Figure 2

(a) Detailed time traces of $D_{\alpha }$ and ECEI signals from the filament zone (ch.2) and near the pedestal top (ch.5). (b) ECEI images of small and large ELM crashes.

Figure 3

Simultaneous emergence and growth of multiple ELM filaments (shot no. 4431). Solid curves are contour lines of the same $\delta T_{*}/{\overline{T}}_{*}$ value representing the approximate boundary of the filaments. The arrows follow the same filament illustrating the counterclockwise rotation.

Figure 4

Multiple bursts of the same filament in a large ELM crash event. (a) First in the series of four bursts. Bottom left sketch depicts the flux surface with the filamentary perturbations and the burst zone entering the ECEI view. The white box arrow indicates the flow velocity of the filaments. (b) Third burst of the same filament, $150\mu \mathrm{s}$ later. Top right sketch is the corresponding model. In each example, the bursting filament develops a narrow fingerlike structure bulging outward.