Electromagnetic Acoustical Dispersion Relationship and the Effect of Superluminal and Radiation Doppler Frequencies of a Moving Dipole in a Stratified Plasma†

Abstract

ABSTRACT The propagation of coupled, electromagnetic and plasma (acoustical) waves generated by a moving and oscillating dipole in an infinitely long, compressible, plasma cylinder surrounded by vacuum is investigated. The fields of the moving sources can be decomposed into two modes—the electromagnetic mode and the plasma (acoustic) mode. These two modes are coupled on the plasma-vacuum boundary. The electric dipole may excite pure, longitudinal, plasma waves since the plasma mode is associated with charge accumulation, but not with a magnetic field It is shown that if an oscillating dipole of frequency ω0 (when Ω= ω—ω0) moves along the axis of the plasma cylinder, it modifies radial wave-numbers of electromagnetic waves in such a way that both the electromagnetic and the plasma (acoustic) waves may propagate without decaying. The coupled plasma and electromagnetic waves do not form a radiation cone analogous to a Cerenkov cone. Requirements for coupled, non-evanescent waves in optical and acoustical spe...