Modeling of metal vapor ionization processes in the cathode spot of a vacuum arc

In this paper the model of the cathode spot of a vacuum arc is considered in the framework of the drift-diffusion representation. The use of the drift-diffusion approximation allows doing without calculation of the functions of particle distribution by energy, as well as without taking into account different energy reactions, which are not associated with change in particle charge. Using the average characteristics of positively and negatively charged ions, while their parameters are taken from experiment, eliminates the need to take into account a large number of basic reactions of interaction between the various components of metal vapor. It is shown that the field intensity of the plasma column is significantly reduced. The given column is surrounded by the bulk charge of slow positive ions, providing high field intensity in front of it. While forming a plasma reaction zone, ionization of the metal vapor occurs mainly in a thin layer in front of the ion cloud, and the ion recombination predominates in this column. Ionization provides a constant elongation of conducting plasma column and moving the bulk charge layer on the outer boundary of the current state, i.e., towards the cathode. This, in turn, leads to a displacement of the local maximum of the electric field and to the displacement of the zone of intense ionization, and provides the movement of the so-called ionization wave. The field intensity in the plasma channel is less than in front of it. The field intensity it is too low and the impact of ionization in the channel does not occur. The key role is played by the loss of electrons due to recombination process.