Helium and oxygen excited states densities in a He-air RF-driven atmospheric pressure plasma jet

Abstract

The volumetric photon emission from a pulsed, RF-driven atmospheric pressure plasma jet was monitored from ultraviolet to the near infrared part of the spectrum. When a small admixture of dry air, as low as ∼0.01%, is added to the helium flow, the helium line intensities decrease, while those of oxygen increase dramatically. To understand the emission trends, a non-equilibrium, collisional-radiative model is developed to estimate He and O excited state densities as a function of relative air concentration. The model is based on a numerical solution of the electron Boltzmann equation for the electron energy distribution function self-consistently coupled to the balance equations for helium and air species. The spectral analyses reveal a good agreement between experiments and modeling, with the latter indicating that a complex interplay between electron kinetics and plasma chemistry is responsible for the substantial changes in emission profiles when He is diluted with a small amount of air.