Features of Electron Emission in Pulsed Forevacuum Plasma-Cathode Electron Beam Sources Based on a Cathodic Arc and a Constricted Arc Discharge

Investigation of features of electron emission in pulsed forevacuum plasma-cathode electron sources based on a cathodic arc and a constricted arc discharge operating at gas pressure of 4–30 Pa (N2, O2, Ar, He) are presented. In these forevacuum electron sources, operating in isobaric mode, the increase in electron emission current (beam current), observed with increasing gas pressure, depends significantly on the type of gas used, as well as on the discharge current. The smallest increase in the emission current is observed when helium is used, and the largest increase is observed when argon is used. At gas pressure below some threshold pressure, which is dependent on the gas type (e.g. for nitrogen and oxygen below 7 Pa), increasing the discharge current leads to an increase in the electron emission efficiency, but at pressures higher than the threshold pressure, the emission efficiency decreases as the discharge current increases. Rise rate of emission current at the front of pulse increases with increasing gas pressure, and this increase in the rise rate of the emission current is more significant for the forevacuum e-beam source based on the constricted arc. The length of the accelerating gap (10–35 mm) has a significant influence on the rise rate of the emission current in the source based on the constricted arc discharge, while in the source based on the cathodic arc this influence is weaker. The observed dependences are related to ionization processes in the accelerating gap of the source and in the electron beam propagation region.