Hydrodynamic phenomena in the cathode spot of the vacuum arc:
Studied the process of displacement of the liquid metal pressure of the plasma from microcraters formed on the cathode during the combustion of a vacuum arc. We formulate the criterion of the origin of the liquid metal shaft on the border of the crater, based on a comparison of a characteristic fluid velocity with the group velocity of the surface capillary waves, which determine the speed of propagation of energy and momentum in the system. In a situation where the height of the shaft significantly exceeds its thickness, there are conditions for the development of the capillary nature of the Rayleigh-Plateau instability, leading to a violation of the axial symmetry of the problem. It is estimated that this instability is responsible for the decay of the shaft into jets, which play an important role in the self-maintenance of the discharge.
The proposed analytical model of the formation of microjets when the displacement of the molten metal by the plasma pressure of the craters formed at the cathode during the combustion of a vacuum arc. The model includes two stages. At the first stage, the movement of the liquid has an axial symmetry; the formation of the surrounding crater of the liquid metal shaft. In the second stage, the axial symmetry is broken as a result of the development of azimuthal instability of the shaft, which corresponds to the tendency to form jets. It is established that the process of shaft decay has a threshold character. The minimum values of the plasma pressure (20-30 MPa) and the electric current (~1.2 A) flowing through the crater, necessary for the formation of jets, are estimated.
