Transition radiation from the zone of injection of a modulated
electron beam spiralling into a magnetoplasma has been identified as whistler
waves propagating 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 densities,
with a diverging radiation pattern and with whistler phase velocities inversely
proportional to the plasma frequency. These studies should contribute to a
wider understanding of the physical processes connected with the injection of
charges in a magnetoplasma – either from a gun on board a spacecraft or in a
plasma chamber – and thus allow the determination of appropriate radiator
characteristics in order to control, to some extent, plasma perturbations and
wave emission in the region of the injector.
Propagation of a nonrelativistic electron beam in a plasma in a magnetic field