DECAY OF THE RETURN CURRENT INDUCED BY A RELATIVISTIC ELECTRON BEAM IN A PLASMA.

It is found experimentally that in a comparatively dense plasma (n//p greater than 10**1**2 cm** minus **3) the return current induced by a relativistic electron beam in a plasma decays because of a lack of electron emission from the collector. At densities n//p less than 10**1**2 cm** minus **3 the decay of the return current is independent of the emissivity of the collector, apparently due to a strong beam-plasma interaction. A plasma collector which is a prolific emitter can be produced by means of an external source (the spark source operates 1 mu sec before the relativistic electron beam is injected), or it can be produced by the relativistic electron beam itself, through an interaction of this beam with the collector material. In the first case the return current does not decay if n//p greater than 10**1**2 cm** minus **3; in the second case, there is a partial disruption of the return current. The degree of residual current neutralization increases with increasing beam current.