Unified simulation of different modes in atmospheric pressure DC discharges in nitrogen

A self-consistent unified model of direct current (DC) gas discharges in molecular gases describing the processes both in the discharge gap and in the electrodes is developed. Numerical simulations of the formation of parameters of various modes of DC discharge in nitrogen at atmospheric pressure in a wide range of current densities have been carried out in the one-dimensional approximation. As a result of numerical experiments, the dependence of voltage drop across the discharge on current density is obtained, which describes various discharge modes: from Townsend through normal and abnormal glow to arc discharge. The distributions of the main mechanisms of heating the electrodes, the values of their temperatures at the boundary with the discharge, depending on the current density, and all plasma parameters for various modes of a dc discharge are presented. It was shown that in the plasma region the dominant role in gas heating belongs to vibrational-translational relaxation, as well as to the reactions of dissociation of N2 molecules by electron impact and quenching of electronically excited N2 molecules. In the cathode layer, the dominant role in gas heating belongs to Joule heating by ion current. The scenario of formation of an arc discharge with free cathode mode when electrons are the predominant charged particles in the cathode layer was shown.