Design of Low Voltage Electron Guns

Abstract

It is shown that by use of a multistage technique in which electrons are drawn from a cathode by a high potential and decelerated to the required final energy, guns can be designed capable of forming beams in which the current is limited only by space charge in the beam itself. The design principles and procedures are given and illustrated by two examples of electron guns giving highly collimated beams and operating at energies of 30 and 500 eV. The measured currents obtained are somewhat greater than the space charge limited beam maximum because of ion neutralization.