The influence of current functions on cathode spot formation and evolution process in metal deuteride cathodes under vacuum arc conditions

Deuterium storage metals are widely used in ion sources as excellent providers of deuterium ions. Many researchers have explored the cathode spot erosion characteristics of metal deuteride cathodes in vacuum arcs. This study establishes a two-dimensional (2D) axisymmetric swirl model to investigate how arc current functions affect the formation and evolution process of cathode spots in metal deuteride cathodes under vacuum arc conditions. The model incorporates fluid dynamic equations, energy equations, and deuterium diffusion equations. The direct current (DC) model is used as the control group, and multiple Gaussian and logarithmic Gaussian distribution current models are compared. The simulation results indicate that when the time-integrated results of the current function are similar, the evaporation-induced erosion rate under a logarithmic Gaussian distribution current function is much lower than that under a Gaussian distribution current function, specifically by one order of magnitude. Moreover, within the logarithmic Gaussian distribution model, a current function with an earlier peak yields a larger deuteride release amount and a smaller evaporation erosion rate, making it a superior current function model. Additionally, when the current reaches over 60% of the total arc current, which corresponds to the cathode surface temperature exceeding 3500 K (with temperature as the underlying driver), evaporation on the cathode spot crater surface increases significantly.