The influence of surface phenomena on the initiation of discharges in vacuum

Breakdown phenomena are initiated by surface conditions in a variety of systems ranging from high-voltage vacuum tubes and friction devices to distillation columns containing unstable molecules. Vacuum tube flashover is a particular case of breakdown attributed to an electron cascade occurring at the insulator surface and causing an electron-stimulated desorption. This model fails to provide an overview of surface-initiated breakdown phenomena or a satisfactory account of the conditioning and deconditioning processes on which flashover reproducibility depends. To further understanding of these phenomena, the authors examine the electrical and mechanical energy dissipation processes in insulators. The dissipation processes arise from the atomic, electronic, and vibrational characteristics of the insulating surfaces and illustrate the influence of point and linear defects on material properties. The authors propose a flashover model based on an electron excitation cascade developing in the surface layers where the defects are concentrated. Physical measurements for breakdown determination and surface treatments for improving dielectric resistance to breakdown under voltage are discussed