Formation of high-energy electron beams in gases of different densities

Abstract

An investigation was made of the formation of beams of fast electrons in different gases at pressures of from 0.01 to 100 kPa. Plots were made of the dependences of the electron beam currents I_e on the gas pressure p for different electric field strengths E. The dependences I_e=f(p) for air were found to intersect the similar dependences for other gases (helium, nitrogen, neon, and argon) at a pressure of p=10.6 kPa and for E=2.3·10⁵ V·cm⁻¹. This fact is explained by the influence of the oxygen ions and atoms on the electron beam formation process. Another experimental result, the appearance of a minimum in the dependences I_e=f(p) for all gases, is explained by defocusing of the electron beam, the appearance of a reverse current, and magnetic neutralization of the beam. Electron beams were obtained having a pulse duration of 15–20 nsec and a current of 10⁵-10⁶ A/m² per unit cathode area.