Solitary perturbaitons prior to the partial collapse of the edge pedestal in KSTAR H-mode plasmas

Abstract

Solitary perturbations (SPs), localized both poloidally and radially, are frequently observed on the KSTAR tokamak within ∼100 µs before the partial collapse of the edge pedestal. The perturbation structure measured by 2D imaging diagnostic [1] is clearly distinguished from the quasi-steady filamentary modes that are routinely observed during the inter-crash period [2, 3]. In particular, the SPs have a low toroidal mode number (typically unity) and smaller pitch angle. The SPs are similar to the irregular mode structure with large amplitude [3] appearing near complete crash. The resemblance suggests that the generation of SPs is strongly connected to the crash mechanism.