Electron cyclotron absorption and emission by superthermal electrons in tokamak plasmas

Abstract

Electron cyclotron wave absorption and emission by mildly relativistic electrons is investigated. The linear theory is developed for a small fraction of fast electrons in order to determine the dynamics of such particles by using transmission measurements in tokamaks. Simple expressions for the dielectric tensor in the presence of a superthermal electron parallel-momentum distribution are obtained by taking the perpendicular energy of this population into account. It is shown that electron cyclotron wave absorption is weakly modified by the shape of the perpendicular-momentum distribution. On the other hand, wave attenuation at the fundamental resonance is significantly affected by the average perpendicular energy for low values of the parallel wave refractive index. A new diagnostic method is proposed to measure the perpendicular electron temperature and the parallel-momentum distribution simultaneously, by using the ordinary and extraordinary modes of polarization.