A Discussion on the early days of ionospheric research and the theory of electric and magnetic waves in the ionosphere and magnetosphere - Waves in a hot plasma

Abstract

In studying wave propagation in a hot plasma, we treat the dynamics of the medium by kinetic theory rather than by continuum mechanics. The theory thus combines Maxwell’s equations with a transport equation in phase space (the Vlasov equation). An outline of the required procedure will be given. Some of the results are in close agreement with those of the fluid treatment provided the specific heat ratio is appropriately chosen. This is generally the case if the phase speed of the waves well exceeds the thermal speed of the electrons and, for a magnetized plasma, the frequency is not close to a harmonic of the cyclotron frequency. New phenomena are found if there are particles whose unperturbed motion is in resonance with the wave field. In the unmagnetized case this results in Landau damping or in instabilities, the latter being analogous to the mechanism of the laser. In the magnetized case there are, in addition, completely new modes of propagation for waves travelling approximately normal to the applied field. Many of these phenomena find direct application in ionospheric phenomena and diagnostics.