Influence of nitrogen and oxygen admixture on the development of helium atmospheric-pressure plasma jet Available to Purchase

This paper presents the experimental and numerical results about the influence of nitrogen (N₂) and oxygen (O₂) admixture on the development of a helium (He) atmospheric-pressure plasma jet (APPJ) in a long dielectric tube. The results revealed that the jet length and the propagation velocity are strongly affected by introducing N₂ or O₂ into the He flow. Specifically, it was observed that a higher N₂/O₂ admixture led to the decrease in the density of both energetic and relative low-energy electrons outside the grounded electrode, which corresponds to the shortening of the jet length. In the He/O₂ mixture, the electrons are easily captured by O₂/O in the region of the plasma bulk. In the He/N₂ mixture, the jet propagation characteristics will change since N₂ has many low-level excitation states that consumed a large number of energetic electrons. The simulation shows that the magnitude of the axial electric field in the jet head depends strongly on the amount of N₂ and/or O₂ in the gas flow. In both cases, the peak electric field is on the order of 5 kV/cm, which is significantly higher than that in pure helium of 3 kV/cm even if the admixture is low (less than 4% N₂ or 2% O₂ in this work). Positive charges of higher density in the jet head are needed to induce a stronger electric field for the jet propagating in N₂(x%)/He and O₂(x%)/He mixtures compared with that in pure He.