Investigation of electron dynamics prior to plasma thermal quench by a gas electron multiplier (GEM) camera

Abstract The gas electron multiplier camera has been used to investigate the electron dynamics in the presence of turbulence and/or a magnetic island in disruptive plasmas on the Experimental Advanced Superconducting Tokamak. Interactions between the micro turbulence and the macroscopic island structure are observed to be mediated by electrons experiencing multiscale instabilities, which are accelerated to generate non-thermal radiation peaks. After comparisons of two typical H-mode disruptive shots, a statistical database is constructed which clearly shows that the amplitude of non-thermal peaks is linearly dependent on the plasma poloidal beta before the thermal quench. Thus, the driving-energy for the electron energization is actually due to the plasma thermal pressure. Although not quantitatively compared with simulations, this paper provides multiple diagnostic data demonstrating electron dynamics under the complex multiscale instability fields. This advances the mechanism causing thermal quench of H-mode plasmas.