Influence of material properties and surface conditions of metal electrodes on vacuum breakdown characteristics in small gaps

Abstract

The vacuum insulation performance of metal electrodes depends on both surface condition and material properties, but their specific roles in the breakdown process remain unclear. The objective of this study is to clarify the specific roles of these factors in the vacuum breakdown characteristics of metal electrodes under small gaps. To identify key material parameters affecting breakdown, a heat conduction model of cathode micro-protrusions was simplified and analytically solved. To validate the model, vacuum breakdown experiments were conducted on five metals (Cu, Cr, Ti, Fe, and W) to measure breakdown voltage and critical emission current density at breakdown (Jb). The experimental results partly validate the model and show that the Nottingham effect significantly impacts Jb. This effect was further fitted using experimental data, and the model was refined accordingly. The results show that, in this study, surface condition has a greater influence on breakdown voltage than material properties. Materials with low local breakdown field can still achieve high breakdown voltage if the field enhancement factor of the surface is low. Electrical conductivity, thermal conductivity, and melting point are key factors affecting vacuum breakdown characteristics under small-gap conditions. Moreover, based on the theoretical model and experimental data, a material parameter combination correlated with Jb is proposed.