AN INVESTIGATION OF LOW-VOLTAGE BEAM DISCHARGE IN HELIUM .1. EXPERIMENT

The collisional regime of the low-voltage beam discharge in helium is investigated experimentally. The spatial distribution of basic plasma parameters along the gap is determined. The conditions under consideration correspond to the case in which the free path of cathode beam electrons is substantially less than the inter-electrode gap, and their energy relaxation length conditioned by binary collisions is substantially greater than the inter-electrode gap. In this case, the distribution function of fast electrons is weakly asymmetric in velocity space. It is shown that the collisional mechanism of beam energy relaxation is realized only for small discharge currents (j(s) less than or similar to 0.1 A cm(-2)). At sufficiently large discharge currents (j(s) greater than or similar to 0.8 A cm(-2)) a more effective wave mechanism of beam energy relaxation switches on in a threshold-determined way.