Retardation of Artificial Plasma Streams Ejected into the Magnetosphere Due to Wave Excitation

Motions of plasma streams ejected from a spacecraft into the magnetosphere and their retardation due to wave excitation have been analyzed in relation to Space Experiments with Particle Accelerators (SEPAC) on Space Shuttle/Spacelab 1. Ion inertial drift induces the electric field in the υ × B direction and the plasma stream keeps moving with constant velocity υ due to E × B drift. However, when the induced charge or energy is dissipated through wave excitation into the ambient plasmas, the plasma stream is subject to retardation. We express the phenomena for Alfven wave excitation by means of an equivalent electrical circuit. When the plasma stream is subject to expansion, the retardation is reduced due to the reduction of the energy density of the plasma stream. It is found that plasma streams shorter than υΩi-1 (Ωi is the Larmor frequency of the ambient plasmas) are subject to less retardation than longer streams and may become gradually longer due to velocity modulation. In the SEPAC experiment, these effects of the expanding and short plasma stream must be taken into consideration, and these analyses are carried out.