Effect of Space Charge on Thermal Field Emission in Vacuum Gaps

Vacuum breakdown research is pivotal in advancing modern technology. Prior to the vacuum gap breakdown, a pre-breakdown process occurs, wherein electron emission from the cathode plays a crucial role. However, electron emission is often limited by space charge effect to further development. Current research on space charge mainly focuses on steady-state processes, lacking a multi-physics model that pushes space charge in real-time based on electric field changes. Therefore, this paper established a thermal-electric field coupled model and developed code to link electron motion with electric field variations in real-time. The simulation of electron emission from micro-protrusions on the cathode surface within a vacuum gap investigates the effect of space charge on thermal-field emission. The results indicate that the pre-breakdown voltage and current under space charge constraints increased by 15.69% and 188.46%, compared to the unconstrained conditions. The cathode material affects the differences in pre-breakdown voltage and current between with and without space charge effects, and tungsten showing significantly greater differences compared to titanium. The non-uniform work function is more significantly affected by space charge than the uniform work function. The decrease in current density under uniform function is twice that under non-uniform function.