Stochastic acceleration of relativistic electrons and plasma heating and current drive with 2.45 GHz frequency at the WEGA stellarator

Abstract

MeV electrons were produced with less than 6 kW of non-resonant 2.45 GHz microwave heating at magnetic fields of 0.3–0.5 T with no applied loop voltage at the WEGA stellarator. The maximum toroidal plasma current, carried by the electrons, was 1 kA. Broadband radiation, similar to synchrotron radiation, was measured in the 0.5–120 GHz range. X-ray radiation from the plasma and directed γ-ray emission from collisions of the electrons with nearby plasma-facing components was measured as well. The acceleration process was modeled by a tail formation due to stochastic interaction with the radio frequency field at the antenna mouth. The characteristic time for tail formation could be reproduced with power modulation experiments.