Investigation of the Electron Beam Generation Efficiency in an Abnormal Glow Discharge in Helium under Pure Conditions

The efficiency of electron beam generation in an abnormal discharge with a cold cathode in helium under clean conditions under a direct current source supply is investigated. The range of measured pressures varies from 2.17 to 10.2 Torr and the voltages from 650 to 3300 V. An electron beam generation efficiency of $\sim 66 \%$ was achieved at a discharge gap voltage of 3300 V and helium pressure of 2.17 Torr. Comparison of electron beam generation efficiency obtained under pure conditions with known literature data is presented and the same value of electron beam generation efficiency $\sim 66 \%$ was demonstrated at shorter discharge gap lengths, lower voltages and higher pressures. It is shown that the electron beam generation efficiency increases under clean conditions. The high efficiency was explained using the effect of cathode modification by working gas (with subsequent change of emission properties of cold cathodes) and the falling part of the dependence of the Townsend electron multiplication factor on the reduced field strength at values greater than 800 Td. The obtained results are of interest for the developers of electron beam generators and allow increasing the energy efficiency of plasma devices.