An approximate theory of electromagnetic wave propagation in a weakly relativistic plasma

An approximate analysis of different types of electromagnetic wave propagation in a weakly relativistic electron plasma is presented. The particular case of wave propagation near the cold plasma cut-offs is considered, and possible applications of the results to diagnostics of magnetospheric parameters are discussed. It is pointed out that wave propagation near plasma resonances in some cases requires relativistic consideration, especially for extraordinary waves. Almost parallel right- and left-hand polarized waves as well as almost perpendicular ordinary and extraordinary wave propagation are considered in detail. It is shown that, in the vicinity of certain frequencies, relativistic effects on the refractive index of these waves cannot be disregarded even when the electron energy is quite small. The problem of wave energy focusing along and perpendicular to the magnetic field is considered with relativistic effects taken into account.