Numerical simulation of the initial expansion process of cathode spots in high-current triggered vacuum arc

Abstract

The cathode spot (CS), as an intense source of inter-electrode arc plasma, plays a predominant role in maintaining the burning of vacuum arc, especially with an inactive anode. Consequently, the dynamics of CSs have a significant influence on the characteristics of the vacuum arc. Many experimental investigations have been devoted to better understanding of the motion of CSs, especially the initial expansion process of cathodes spots in high-current triggered vacuum arc. It has been indicated that the motion characteristic of cathode spots is greatly influenced by external axial magnetic field (AMF). In this work, a method is established to simulate the initial expansion process of CSs in high-current triggered vacuum arc, based on the proposed stepwise model of the motion of a single CS1. In this method, every new CS can be ignited in any direction around the old one with certain probability, which is connected with the magnetic field around the position of the old CS. With this approach, the initial expansion processes of CSs in free-burning and AMF-stabilized high-current triggered vacuum arc are simulated numerically with CSs initially uniformly distributed on a ring. The self-generated transverse magnetic field at the position of every CS is calculated by commercial software ANSYS with the current distribution in contact plate taken into account2. Simulation results agree well with relevant experiment results. Simulation results show that CSs expand faster without external AMF than that under AMF, and external AMF has significant influence on the distribution of CSs on the cathode surface, e.g., more and more CSs appear inside the ring when external AMF is present. Furthermore, the results also indicate that the expanding ring structure of CSs is unstable, and AMF can accelerate the breaking of the ring.