Formation of Positively Charged Electron Beams in the Presence of Secondary Electron Emission

Abstract

A condition has been found for a positively charged electron beam to be formed when secondary electrons, knocked out by the beam electrons from the collector, are present in the drift space. The parameters of total electron space charge compensation by positive ions for different collector materials and different ions have been calculated. Two types of axially symmetric positively charged electron beams have been experimentally investigated: beams with the current density maximum located on the axis of the drift tube and beams with the current density maximum located at a distance from the axis. Estimates based on measurements of the radial potential distribution in the drift tube have shown that the excess positive ion charge created in the second case should be three times that in the first case. This can be explained by the accumulation of ions in the potential well-formed inside an axially symmetric electron beam of the second type.