Observation of edge turbulence spread by ECEI on the ELM-crash-suppressed plasmas in the KSTAR

Abstract

The structure and dynamics of the ELM and edge turbulence modified by n=1 RMP have been studied during the ELM-crash-suppression phase by applying correlation analysis techniques on the measured ECEI signals. The ECEI shows that filamentary modes remained at theedge with frequent bursts during ELM-crash-suppression phase. The filamentary mode fluctuates in the range of 20 kHz and the dynamics of the mode seems to be violent and complex compared to the ELMing H-mode phase. Correlation analysis shows corresponding fluctuations have long poloidal wavelength (or small poloidal wavenumber kθ<1 cm−1) with smaller size compared to the filamentary mode, and average group velocity of ∼3 km/s along the electron diamagnetic direction, parallel wavelengths in the range of 2<λ||<8 m. The characteristic size in the order of kθρs∼0.1 and velocimetry analysis suggest the resistive ballooning mode is a strong candidate for edge fluctuation in the ELM-crash-suppression phase.