Investigation on the Effect of the Self-generated Metal Vapour on the Cathode Spot Formation in Vacuum Arc by Molecular Dynamics Simulation

Contact erosion is one of the key problems that limit the development of vacuum circuit breakers at higher voltage levels. Contact erosion in vacuum arc is the result of the plasma-surface interactions, located at the positions of cathode spots. Simulation studies on cathode spot dynamics have been of great significance in investigating the mechanism of contact erosion. Previous cathode spot simulations commonly assumed that the leftover plasma ions have a constant density function, which initiate and maintain the cathode spot. However, this assumption has a critical limitation as it does not include the self-generated metal vapour from the cathode spot, which plays a dominant role in sustaining the cathode spot. In this work, the contribution of the self-generated metal vapour on the development of an individual cathode spot is investigated, by studying the effect of back ions. Based on a self-consistent cathode spot model developed by the Molecular Dynamics method, comparisons are made among different cases where the contributions of leftover plasma ions and back ions are controlled. This work models the self-sustaining cathode spot without continuous input of leftover plasma ions for the first time. Simulation results show that the leftover plasma ions are necessary to initiate a cathode spot, while the self-generated metal vapour is sufficient to sustain the development of the individual cathode spot. The simulation results are validated by the comparable erosion speed of the crater depth to the experimental values.