Investigations of vacuum arc cathode spots with high temporal and spatial resolution

There are two principal approaches for gaining knowledge about the processes occurring in the cathode spot of a vacuum arc: the quasi-stationary model (evaporation model) and the nonstationary or explosive model (ecton model). The existence of two fundamentally different approaches for treating the same phenomenon results from the fact that there is no consensus of opinion among researchers regarding the principal parameters of the cathode spot. A reason for this is that the severe conditions in the cathode spot make direct observations very difficult. The main difficulty is related to the fact that a cathode spot has small dimensions (on the order of 10-100 /spl mu/m) and moves chaotically over the cathode surface with a velocity of up to 100 m/s. Therefore, it is felt that a deeper insight into the cathode spot operation mechanism can be provided by experimental equipment and techniques showing the highest temporal and spatial resolution achievable today. The paper gives a review of the experiments concerning the physical mechanism of the current passage in the cathode spot of a vacuum arc. The paper discusses the structure and behaviour of cathode spots, cathode spot lifetime and current density, current cell model, and model of processes in a vacuum arc.