Influence of space charge density on electron energy distribution function and on composition of atmospheric pressure He/O2/air plasmas

Abstract

Atmospheric pressure non-equilibrium plasma represents an efficient source of reactive species for different kinds of applications. Rich chemistry of such plasmas develops on longer time scales and is difficult to handle by kinetic models so global models are often applied to study such processes. The Maxwell-Boltzmann (MB) distribution is often used in global modelling of these non-equilibrium systems, even for the calculation of electron rate coefficients. In order to test the sensitivity of plasma composition on the space charge density and consequently on the assumed electron energy distribution function (EEDF), the zero-dimensional global model is applied to the helium/oxygen mixture (0.5% of O2 with humid air impurities. To test the effect of the distribution function on global models we have included the data calculated based on the non-equilibrium EEDF for the processes where often exponential Arrhenius-like formulae as a function of the effective temperature are used. The initial calculation showed that the change in the form of distribution function mainly affects the processes with thresholds considerably higher than the mean electron energy while it does not change much the rates for the processes with the thresholds and peaks of the cross sections in the region of the mean energy. We have calculated variations of the EEDF with the charge density and the resulting changes in chemical kinetics.