Electron-cyclotron absorption and emission: Vexatae quaestiones''

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 a...