Experimental signatures of electron cyclotron wave energy condensation in magnetic islands

Abstract

Bifurcation of the electron temperature perturbation (ΔT e) in magnetic islands due to electron cyclotron current drive (ECCD) is reported for the first time in toroidal plasmas. In this DIII-D experiment ΔT e spontaneously increases by 50% in a growing 2, 1 island which in turn rapidly shrinks, consistent with improved stabilization by the ECCD due to the temperature bifurcation. This non-linearity of ΔT e maps out a hysteresis in the island evolution cycle, in qualitative agreement with the theoretically predicted radio frequency current condensation effect Reiman and Fisch 2018 (Phys. Rev. Lett. 121 225001). Therefore, this observed bifurcation can be critical for the avoidance of disruptions caused by tearing modes in tokamaks.