Influence of different O2/H2O ratios on He atmospheric pressure plasma jet impinging on a dielectric surface

Abstract

Abstract A two-dimensional (2D) axisymmetric fluid model is built to investigate the effect of different O2 and H2O admixture on the plasma dynamics and the distribution of reactive species in He atmospheric pressure plasma jet (APPJ). The increase of O2:H2O ratio slows down both the intensity and the propagation speed of the ionization wave. Due to the decrease of both H2O ionization rate and H2O Penning ionization as well as the stronger electronegativity of O2, the increase of O2:H2O ratio results in a significant reduction of electron density in the APPJ, which restricts the occurrence of electron collision ionization reactions and inhibits the propagation of plasma. The excitation energy loss of O2 is not the reason for the weakening of the plasma ionization wave. The densities of O2 +, O− and O2 − increase with the rise of O2 admixture while H2O+ decreases due to the decrease of electron density and H2O concentration. OH− density is affected by both the increase of O− and the decrease of H2O so it shows a peak in the case of O2:H2O = 7:3. O is mainly produced by the excitation reactions and the electron recombination reaction (e + O2 + → 2O), which is directly related to the O2 concentration. OH is mainly produced by e + H2O → e + H + OH so the OH density decreases due to the decrease of electron density and H2O concentration with the increase of O2:H2O ratio. On the dielectric surface, when the propagation of the streamer extinguishes, O flux shows an upward trend while the OH flux decreases, and the propagation distance of O and OH decreases with the increase of O2:H2O ratio.