An experimental study of the dynamics of formation of plasma in a vacuum-arc discharge

An experimental study is made of the dynamics of formation of plasma in a vacuum-arc discharge (VAD) at different currents and different transverse dimensions of $\text{CuCr}50$ electrodes. High-speed multipleframe photography is used to obtain the time dependence of the current channel diameter and determine the rate of plasma expansion. It is demonstrated that the rate of expansion under the experimental conditions is independent of the discharge current, as well as of the presence or absence of external axial magnetic field. Two modes are identified, which differ from one another by the rate of expansion. Experiments are performed with anodes and cathodes of different diameters in the range of currents from $2$ to $15$ kA. It is demonstrated that, with electrodes of different sizes, a discharge initiated at the cathode center expands with time to the size of the smaller electrode while retaining the cylindrical shape. The anode temperature is calculated for two modes in view of the variation of the source power and of the transverse dimension of the zone of heating. It is demonstrated that the anode spot in the mode of rapid expansion is formed under insignificant heating of the anode. In the case of slow expansion, a strong heating of the anode is possible, under which its intense evaporation occurs. The anode temperature is calculated in view of the evaporation losses for modes with different numbers of jumpers arising as a result of the breaking of vacuum switch contacts.