Criteria for the Formation of Liquid-Metal Jets in the Cathode Spot of a Vacuum Arc Discharge

The formation of jets is studied that accompanies the extrusion of a molten metal under the action of the plasma pressure from microcraters formed in the cathode spot during an operation of vacuum arc discharge. We have proposed an analytic model of the melt splashing that demonstrates the threshold behavior: the extrusion rate has to exceed some threshold that is caused by capillary forces. These forces, on the one hand, lead to the reverse motion of the extruded liquid with the Taylor-Culick speed and, on the other hand, to the azimuthal instability development of the liquid-metal rim on the crater contour. The threshold values of electric current flowing through the crater and plasma pressure, at which the formation of liquid-metal jets starts, are estimated.