Features of the microwave radiation under the fan instability development and accelerated electron interaction with magnetic ripples in the FT-2 tokamak ohmically heated plasma

Abstract

Results of observation of anomalously intense microwave radiation (MR) in the electron plasma frequency range of 10–20 GHz that is generated continuously during ohmic heating of moderately dense plasma in the FT-2 tokamak are presented. Its appearance is associated with development of the “fan” plasma instability, and the presence of a large number of the local ripples of the toroidal magnetic field. It was found that MR is accompanied by the short gigantic and less intense flashes in the range of magnetic broadening of the first harmonic of the electron gyrofrequency (57–75 GHz). As is known, the latter occurs upon maser amplification of the synchrotron radiation of accelerated electrons interacting with the harmonics of local magnetic ripples in an autoresonance cyclotron mode. In our conditions, due to the nonlinear transformation of plasma waves into electromagnetic ones under the buildup of the fan instability, collective radiation (CR) is generated. Therefore, an abnormally high MR-intensity is probably due to CR maser amplification, whereas gigantic flashes occur during the self-excitation of maser amplifier under suitable conditions.