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

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 $k_{\theta}<1$ cm$^{-1}$) with smaller size compared to the filamentary mode, and average group velocity of $\sim3$ km/s along the electron diamagnetic direction, parallel wavelengths in the range of $2<\lambda_{||}<8$ m. The characteristic size in the order of $k_{\theta}\rho_s\sim0.1$ and velocimetry analysis suggest the resistive ballooning mode is a strong candidate for edge fluctuation in the ELM-crash-suppression phase.