Electromagnetic radiation from a source in a plasma

Abstract

The problem of determining the electromagnetic radiations from a given charge-current distribution situated in a plasma in the presence of a uniform external magnetic field is solved. Explicit expressions for the asymptotic electromagnetic fields are given for the case of a cold plasma. The resulting expressions simplify considerably in the case where the frequency of the wave is much less than the electron gyrofrequency or the plasma frequency. Here it is found that the radiation is confined to a cone whose generator makes a constant angle of about 20[deg] with the external magnetic field. The fields diverge on this cone but the divergence is so weak as to cause no physical difficulty. Another result of interest is that a purely longitudinal current, of which the simplest example is a pulsating spherically symmetric charge distribution, will radiate in this medium while, as is well known, such a charge distribution will not radiate in an isotropic medium. As an example, the low-frequency spectrum of radiation from a radial burst of charge is calculated.