Influence of gas flow on the axial distribution of densities, temperatures and thermodynamic equilibrium degree in surface-wave plasmas sustained at atmospheric pressure

Abstract

In this paper, a discussion about the influence of the gas flow on the axial distribution of plasma densities, temperatures and thermodynamic equilibrium degree in argon surface-wave discharges sustained at atmospheric pressure is presented. It was found that increasing the gas flow produces a decrease in gas temperature and electron density which is explained in terms of a decrease of residence time of both heavy particles and electrons. Moreover, the dependence of the dynamics of argon molecular ions on gas temperature also explains the decrease in electron density and the increase in the population of 4p excited levels. Thermodynamic equilibrium is also affected by gas flow, whose increase drives the 5p levels out of partial Saha equilibrium, although they remain in the collisional regime for their population processes. Furthermore, the linear power density was measured to complete the characterization of surface-wave plasmas with different gas flows. From the linear power density, it is possible to conclude that increasing the gas flow means that the energy supplied to the discharge is being used not only for ionization processes, but also for the excitation of argon atoms from the ground to metastable states, thus, increasing the populations of 4p levels.