Experimental study of dynamics of plasma formation in a vacuum-arc discharge

Experimental study of plasma formation dynamics in a vacuum arc discharge (VA) at different current values and different dimensions of CuCr50 electrode cross-sections has been carried out. With the use of high-speed multiframe photography time dependences of the current channel diameter and plasma expansion speeds have been determined. It has been demonstrated that plasma expansion speed under the experiment conditions does not depend on the current value, nor it does on the presence/absence of the external axial magnetic field. Two plasma expansion modes differing in speed have been determined. The experiments have been carried out with anodes and cathodes of different diameters and current values of 2 to 15 kA. The experiments show that when the electrodes differ in size, the arc discharge initiated in the center of the cathode expands with time until it reaches the size of a smaller electrode while keeping a cylindrical form. Anode temperature calculations for two plasma expansion modes were made with consideration of the change of the power source and the dimension of the heating area cross-section. It was shown that in the high-speed expansion mode an anode spot appeared by insignificant heating of the anode. In the low-speed expansion mode high heating of the anode is possible, with anode intense evaporation taking place. The anode temperature was calculated considering evaporation loss in the modes with switching the current.