A relativistic theory of plasma cut-offs

Abstract

It is pointed out that at frequencies near the plasma cut-off frequencies, the corrections to wave refractive indices in a cold plasmaN 0due to the contribution of ions and relativistic effects can be of the same order of magnitude or greater thanN 0. Expressions for wave refractive indicesN taking into account these corrections are derived in a limiting case |N| ≪ I. It is shown that the increase in cut-off frequencies due to effects of ions is negligibly small unless the electron plasma frequency is well below the electron gyrofrequency. The decrease of the cut-off frequencies due to relativistic effects is significant (≥ 1%) only in a rather hot plasma (T e≥ 1 keV), which may be observed in a plasma sheet region of the Earth's magnetosphere and in astrophysical conditions. These effects appear to be particularly important in a strongly anisotropic plasma (the electron perpendicular temperature is noticeably greater than the parallel one).