Formation of pulsed large-radius electron beam in the forevacuum pressure range by a plasma-cathode source based on arc discharge

Abstract

The research on generation and propagation of large-radius low-energy (up to 10 keV) electron beam with millisecond pulse duration by the plasma-cathode electron source in the forevacuum pressure range (3–30 Pa) is presented. An arc discharge with cathode spot has been used to generate emission plasma with millisecond pulse duration. Large hollow anode and ball-shaped redistributing electrode have provided formation of arc plasma with emission surface of 100 cm2; emission plasma boundary has stabilized by metallic mesh. It is established, that gas type and gas pressure affect the parameters of the arc discharge. In case of gases with greater ionization cross section (argon, nitrogen), an increase of gas pressure has led to a decrease of arc voltage and to an increase of emission plasma density. Gas with small ionization cross section (helium) had weak effect on the arc discharge parameters. An increase of emission window in the anode has provided an increase in radius of the electron beam and an increase of efficiency of electron extraction from the arc plasma; on the other hand it has led to an increase of influence of back-streaming ion flow on the electron emission and led to a decrease of maximal operating gas pressure. Reducing the geometric transparency of the emission mesh, as well as the use of gas with small ionization cross section have provided an increase in the maximal operating pressure of the source of large-radius electron beam. It is established, that in the forevacuum pressure range, large-radius electron beam is efficiently generated in the investigated range of distances from the extractor up to 35 cm.