Beam-Plasma Interactions and Radiation Generation during the Ejection of Electronand Ion Beams in Space

摘要

Multi-dimensional electrostatic and electromagnetic particle simulations are usedto investigate the nature of beam-plasma interactions and radiation generation during the injection of dense electron beams into the ionosphere from spacecraft. The nature of the injection process is determined primarily by the relative value of two characteristic time scales: the beam stagnation time t s and the plasma response time t rp When t s < trp, spacecraft charging is significant and most of the beam electrons are drawn back into the spacecraft. When ts>trp, vehicle charging is reduced and the beam propagates away from the source. In this latter case there is strong beam-plasma turbulence which destroys the coherence of the beam within one or two gyroperiods. The spatial distribution of the beam has the form of a hollow cylinder near the source. As the beam propagates away from the source, the cylinder becomes increasingly filled. Return currents are associated with the field-aligned flow of ambient electrons, while current closure is provided primarily by the cross-field motion of the ions. The beam-plasma interaction leads to the formation of coherent current structures. Whistler waves