Electron-cyclotron absorption and emission: ‘‘Vexatae quaestiones’’

Abstract

The salient features of the theory of electron-cyclotron absorption and emission for the parameter range for which the radiation spectrum has a line structure are reviewed and contrasted with erroneous results of a recent paper by Arunasalam [Phys. Fluids B 4, 1643 (1992)]. In particular, (i) the relativistic and nonrelativistic forms of the dielectric tensor relevant to describing the electron-cyclotron absorption are considered, their range of validity is displayed, and on this basis an incorrect suggestion in the above paper on how to obtain the relativistic dielectric tensor from the nonrelativistic one is refuted; (ii) the crucial role of the thermal effects on the mode polarization, which in turn affects the absorption profile around the fundamental frequency, is emphasized, showing that using a ‘‘Trubnikov O-mode factor’’ as advocated in the above paper is not correct; (iii) the profile of the absorption around the fundamental frequency results to be single humped in all cases, in contrast to the assertion in the above paper that the absorption profile of the first harmonic O mode is double humped; (iv) the radiation from a nonuniformly magnetized plasma is evaluated for a bi-Maxwellian electron distribution showing, in particular, that the nonrelativistic treatment used in the above paper is incorrect for perpendicular propagation; (v) an expression for the local radiation temperature obtained in the above paper and upon which the analysis of the emission spectra of supershot plasmas in the Tokamak Fusion Test Reactor (TFTR) has been based by Taylor et al. [Proceedings of the Eighth Workshop on Electron Cyclotron Emission and Heating, Gut Ising, Germany, 1992, (Max-Planck Institut für Plasmaphysik, Garching, 1993), IPP III/186, Vol. 1, p. 277] is shown not to be valid.