Dynamics of Molten Metal Jet Formation in the Cathode Spot of Vacuum Arc Discharge

Molten metal jets formation during operation of vacuum arc discharge for a wide range of cathode spot cell sizes and electric currents has been studied. In our model, this process has been divided into two stages. At the initial one, the melt is extruded from the microcrater on the cathode surface under the action of plasma pressure. As a result, a liquid-metal toroidal rim is formed around the crater. This process has been numerically simulated in the framework of the two-dimensional axisymmetric heat and mass transfer problem in the approximation of viscous incompressible liquid. At the next stage, the geometry of the problem loses axial symmetry due to azimuthal instabilities development (the liquid metal rim breaks into jets). The development of the instabilities of the rim is analyzed in terms of dispersion relations for surface waves. It is shown that maximum increments correspond to the capillary instability of the Plateau-Rayleigh type. The time of formation of liquid metal jets and their probable number are estimated.