Whistler emission through transition radiation by a modulated electron beam spiralling in a magnetoplasma

Transition radiation from the zone of injection of a modulated electron bea m spiralling into a magnetoplasma has been identified as whistler waves pro pagating quasiparallel to the external magnetic field. The characteristics of the radiation are similar to the emission by localized sources, such as loop antennas and electric dipoles: resonance-cone structures at low plasma densities and energy flow along the external magnetic field at higher dens ities, with a diverging radiation pattern and with whistler phase velocitie s inversely proportional to the plasma frequency. These studies should cont ribute to a wider understanding of the physical processes connected with th e injection of charges in a magnetoplasma - either from a gun on board a sp acecraft or in a plasma chamber - and thus allow the determination of appro priate radiator characteristics in order to control, to some extent, plasma perturbations and wave emission in the region of the injector.