THE IONIC COMPOSITION OF THE NONIDEAL PLASMA PRODUCED BY A METALLIC SPHERE ISOTHERMALLY EXPANDING INTO VACUUM

A physical model of the non-ideal plasma of a vacuum arc cathode flare is presented. Expressions for the electronic transport coefficients valid for the condensed and plasma states are obtained and a method for the calculation of the equilibrium ionization state of the plasma is developed for a wide range of pressures and temperatures. To study the conditions under which the cathode plasma ionic composition forms, a modelling problem of a metallic sphere expanding into vacuum is solved. The non-equilibrium plasma ionic composition is found by solving the balance equations for particles, in which the reaction rates are calculated in a quasi-classical approximation by taking into account the possibility of the formation of frozen ionization states. The numerical simulation carried out has determined the ionic composition of the high-density regions (10(21)-10(18) cm-3), with frozen states playing an essential part in its formation. The obtained theoretical values of the ionic composition are not at variance with experimental results, including those for stationary vacuum arcs.