Sawtooth stabilization by localized electron cyclotron heating in a tokamak plasma

Abstract

Sawtooth oscillations (STO) in the Ohmically heated WT-3 tokamak are strongly modified or suppressed by localized-electron cyclotron resonance heating (ECH) near the q=1 surface, where q refers to the safety factor. The efect of ECH is much stronger when it is applied on the high-field side as compared to the low-field side. Complete suppression of the STO is achieved for the duration of the ECH, in most cases, when it is applied on the high-field side of a low-density plasma, provided the ECH power exceeds a threshold value. The STO stabilization is attributed to a modification of the current-density profile by hot electrons generated by ECH, which reduces the shear in the q=1 region.