10th International workshop on "Stochasticity in Fusion Plasmas (SFP)"-"3D physics in stellarators and tokamaks"

Pedestal dynamics between type-I ELMs have been studied with the poloidal correlation reflectometer and high-frequency magnetic probes in EAST high confinement mode plasmas. The experimental results indicate that the electron temperature recovers faster than the density pedestal after an ELM collapse, and the increasing temperature gradient stimulates a magnetic coherence mode (MCM, f~25kHz). Once this mode is excited, the pedestal temperature almost saturates until the onset of the next ELM. With the increase of the pedestal density gradient, MCM is suppressed and a high frequency electromagnetic mode (HFEM, f~280kHz) becomes dominant, which in return decelerates the growth of the pedestal density. At the later stage, the HFEM disappears and the MCM recover again just prior to onset of the next ELM. The wavelet-bispectrum analysis has been applied to the magnetic fluctuations signal and the result reveals that the recovery of the MCM gains energy from the high-frequency magnetic turbulence. At the last stage, it appears that the sharply increasing MCM plays a critical role in triggering the onset of type-I ELM in this scenario.
 

pedestal dynamics;magnetic coherent mode;wavelet-bispectrum