Evidence of perpendicular flow bifurcation at the onset of ELM-crash suppression

The evidence of perpendicular electron flow ($v_{\bot ,e} $ \begin{figure}[htbp] \centerline{\includegraphics[width=0.23in,height=0.18in]{140720171.eps}} \label{fig1} \end{figure} ) bifurcation at the onset of ELM-crash suppression has been measured using electron cyclotron emission imaging (ECEI) system [1] for the first time in KSTAR. The ECEI has shown that (1) resonant magnetic perturbation (RMP) enhances small scale turbulent fluctuations in the edge toward the ELM-crash suppression phase, (2) the induced turbulence regulates growth of the ELM filament via nonlinear interaction between them [2]. Cross spectra and correlation analysis among the ECEI channels revealed that the ELM crashes get suppressed along with a rapid reduction of $v_{\bot ,e} $ \begin{figure}[htbp] \centerline{\includegraphics[width=0.23in,height=0.18in]{140720172.eps}} \label{fig2} \end{figure} close to zero (small but finite value) together with decrease of its shear. The $v_{\bot ,e} \sim $0 km/s \begin{figure}[htbp] \centerline{\includegraphics[width=0.78in,height=0.18in]{140720173.eps}} \label{fig3} \end{figure} is sustained during the ELM-crash suppression even under a large variation of RMP current and external torque and when this condition is violated, ELM crashes are reappeared. [1] G.S. Yun et al., Rev. Sci. Instrum., 81 (2010) 10D930 [2] J. Lee et al., Phys. Rev. Lett., 117 (2016) 075001