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O2 impurity in the working gas of an He/CF4 atmospheric pressure plasma jet (APPJ) can affect the discharge dynamics and the density of reactive species. Therefore, a two-dimensional (2D) fluid model is built in order to explore the influence of an O2 admixture on the propagation and F-containing species distribution of He/CF4 APPJ. The addition of 0.1% O2 accelerates the ionization rates of APPJ due to the increase of Penning ionization reactions of O2, resulting in the increases of axial speed and F-containing reactive species (CF4+, CF3+, CF2+, CF+, F+, CF3, F, CF3−) when APPJ approaches the dielectric surface. The addition of O2 has the inhibitory effect on the rise of some F-containing reactive species (CF3+ and F). As O2 concentration increases to 2%, the concentration of F-containing reactive species shows a downward trend due to the increase of excitation energy loss and an electron attachment reaction of O2. Different from the axial speed, the radial speed decreases continuously with the increase of O2 because of the high O2 concentration on the dielectric surface when APPJ propagates radially. This also results in a reduced distribution of reactive species fluxes. The excitation energy loss and electronegativity of O2 and CF4 in the case of He + 0.5% CF4 + 0.5% O2 have been presented in this paper. It is discovered that excitation energy loss of O2 is stronger than that of CF4, but the electronegativity of CF4 is stronger than that of O2. [ABSTRACT FROM AUTHOR]

In this paper, a two dimensional (2D) axisymmetric fluid model is built to study the effect of the ratio of CF4 admixture on the plasma dynamics and F-containing species concentration in He atmospheric pressure plasma jet. The steady mole fraction distribution of He and CF4 is first studied, which presents that the mole fractions of CF4 show peaks at 5 mm from the symmetry axis on the dielectric surface due to the dual influences of the boundary layer effect and air mixing. The CF4 admixture enhances the propagation speed of ionization wave, and the axial velocity reaches the peak value in the case of He + 1.5% CF4. The conversion from the ring-shaped plasma–surface interaction to a solid-disk one results from the addition of CF4. The Penning ionization of CF4 accelerates the plasma jet propagation within 1.5% CF4. However, the excitation energy loss and electron attachment caused by the addition of CF4 also quench the propagation of plasma jet, which become obvious in the case of 2% CF4. F-containing groups (CF4+, CF3+, CF3−, F−, CF3, and F), mainly produced by the Penning ionization reaction, electron attachment reaction, and He+ + CF4 → He + CF3+ + F, also show peaks for He + 1.5% CF4. On the dielectric surface, as the radial distance increases, the ratio of F-containing neutral species (CF3 and F) to O atom at 200 ns decreases due to the increase of O atom concentration and then increases at the streamer head because the surface flux of CF3 reaches the maximum value. The maximum surface flux radial distribution distance for ratio of F-containing species to O atom, CF3 and F appear in the case of 1.5% CF4. [ABSTRACT FROM AUTHOR]

Based on a 2D axisymmetric plasma fluid model, the effect of the levels of O2 admixtures on the plasma dynamics of an atmospheric pressure He plasma jet incident on a dielectric surface situated normal to the jet axis has been studied. The introduction of O2 admixture in the feedstock gas changes the shape of the discharge ionization rate that approaches the target surface from a ring to a solid disk. As the streamer extinguishes radial propagation along the dielectric surface, comparatively larger plasma-surface contact areas were obtained for O2 additions to the He plasma of less than 0.5% relative to that for the discharge in pure He, while in the case of 2% O2, the radial propagation distance dropped off significantly. The propagation of an ionization wave peaked in the range 0.2%–1% for the O2 admixture. The enhanced ionization reactions are considered to predominate for small concentrations of O2 as additive, and the negative role played by the excitation energy loss and the attachment of electrons to O2 is more important with the addition of 2% O2. There was a remarkable incremental gain in the flux intensity of O on the surface center, while the flux of N was mainly concentrated on the streamer head. The magnitude of the O flux on the surface showed a peak at the 0.5% O2 admixture level, and the flux of O3 on the surface was directly proportional to the O2 concentration. [ABSTRACT FROM AUTHOR]