Practical design of triple junction for a 90 kV electron gun

Abstract

High-voltage electron guns can commonly be damaged by surface flashover, which can occur across the insulator surface of the gun as a result of electron emission around the triple junction structure. Using secondary electron emission avalanche (SEEA) theory as a basis, the triple junction in a 90 kV electron gun is optimized in this work to avoid damage from the effects of surface discharges. A metal shielding structure is used to reduce the surface flashover caused by electron emission and ensure that the electron gun provides reliable high voltage performance. The aim of the proposed design method is to reduce the field strength that occurs within the electron gun structure. Simultaneously, it is shown that SEEA theory can provide a reasonable explanation for and a solution to the flashover phenomenon that occurs on the insulator surface. In addition, the metal shielding structure used to address the high voltage vacuum discharge phenomenon proves to be an effective design method. Experiments performed on the electron gun for a 90 kV X-ray tube demonstrate that the proposed design method has a favorable effect on control of the flashover phenomenon.