Kinetics in atmospheric-pressure discharges in helium mixtures with nitrogen and oxygen
Résumé
This work studies different elementary processes controlling the global discharge behavior and the kinetics of the main charged and neutral species in helium / nitrogen / oxygen plasmas. Numerical simulations of the electron impact reactions in helium-based plasmas are performed using the IST- LoKI computational tool. The influence of He metastable states and consequent superelastic and stepwise ionization collisions are documented, as well as the influence of the admixture of air gases with different collision cross sections and ionization thresholds. For a relative density of the molecular gas of only 0.1%, the calculated ionization rate coefficient is shown to be higher than in pure He. Particle balance equations have been solved for a reduced He-N2 kinetic scheme, considering the local application of a transitory electric field with 50Td maximum amplitude. The key role of the N2 admixture in He and of various elementary processes, especially Penning reactions, on the ionization degree of the plasma is pointed out.