Observation of fast electron redistribution during saturated kink mode in high β

Abstract

In the EAST tokamak, we have developed an internal transport barrier (ITB) high- confinement mode (H-mode) scenario characterized by dominant electron heating and centrally peaked electron temperature profiles, facilitated primarily through the combustion of lower hybrid current drive (LHCD) and electron cyclotron radio heating (ECRH). Hard X-ray (HXR) diagnostics reveal a marked increase in the population of fast electrons with energy from 30 keV to 80 keV, concurrent with augmented ECRH power during H-mode plasma operations. This surge in fast electron population precedes the formation of the electron temperature ITB (Te-ITB). Within the Te-ITB H-mode discharge, a mild and long-lived m/n=1/1 mode (where m and n denote the toroidal and poloidal mode numbers, respectively) emerges proximal to the ITB region. This mode precipitates a redistribution of fast electrons, contributing to an increase in the safety factor near the magnetic axis and thereby promoting the stability of the Te-ITB. Furthermore, we explore the influence of fast electrons on plasma pressure and examine the effects of ion cyclotron radio heating (ICRF) on the distribution of fast electrons. Strategies to maintain the m/n=1/1 mode at a moderate amplitude are also discussed, highlighting their significance in the sustained management of Te-ITB.