Spacecraft interactions with beam emissions

Summary form only given, as follows. This is an overview on effects of charged beam emissions from spacecraft. In the classical situation, the spacecraft potential increases with the beam current. At high beam currents, new phenomena may ensue. We discuss two such phenomena. (1) A virtual electrode may appear in the beam near the exit point for an unneutralized beam with a high current density. Partial beam return occurs. The phenomenon is more prominent for ion beams than electron beams, and more so for wide ion beams. (2) Supercharging may occur for high beam current emissions with beams diverging under the repulsive force of the beam space charge. Those beam electrons, or ions, with exceedingly high angular momenta cannot return to the spacecraft even if the spacecraft potential reaches, or even exceeds, that of the beam energy. This phenomenon is prominent for narrow unneutralized beams with high current density. These effects affect the spacecraft potential. We present theories and computer simulations, and also provide interpretations to space observations in support of these ideas.