Plasma chemistry in the free-burning Ar arc

Recent ambitions have been aimed at modelling of a free-burning arc in argon by means of a self-consistent description of the arc plasma and the electrodes avoiding assumptions of equilibrium. As a next step, the present work deals with the impact of the reaction chemistry used in non-equilibrium modelling. A set of reactions accounts for elastic scattering, excitation and de-excitation in collisions with electrons and atoms, step-wise ionization, recombination and spontaneous emission. A simple chemistry model based on the approximation of prompt ionization, a model with an effective excited level, and a model implying higher excited levels of argon atoms are considered. The results obtained show that all three models are capable of predicting the arc characteristics. They deliver values of electric current density, electric conductivity, arc voltage, electron and heavy particle temperature which are close to each another. The simple model can serve as a fast-track evaluation of the arc characteristics, and for sensitive studies of the impact of model parameters. The extended model allows obtaining the populations of individual and effective levels giving rise to important radiative transitions.