Microdischarges on an electron gun under high vacuum

Abstract

Two types of microdischarges on an electron gun operated at 100 kV—one of which occurs between the high-voltage electrodes and the other over the insulator surface—were experimentally examined, by concentrating the greatest interest on gas molecules on the respective surfaces. Microdischarges between the high-voltage electrodes in high vacuum were induced by gas molecules adsorbed on the electrode surfaces. Argon glow cleaning showed a distinct conditioning effect on the electrode surfaces. Microdischarges over the insulator surface were enhanced by the outgassing from the insulator. The reason is that the insulator surface with a high density of gas molecules causes high yield secondary electron emission, leading to positive charge-up over the insulator surface. Thermal degassing for the electrodes and insulator showed a conditioning effect to reduce microdischarges between the electrodes and over the insulator surface.