Modeling of the particle fluxes of a helium plasma jet onto water surface

The interaction between an atmospheric pressure plasma jet (APPJ) and an aqueous solution has great application prospects in biomedicine and many other fields. Reactive species adjacent to a water surface is critical to the activation of APPJ-treated water, which is affected by both the water evaporation and the admixture of ambient air. In this paper, taking He APPJ as an example, a two-dimensional (2D) cylindrically symmetric fluid model is developed to obtain the spatial distributions of gas components before discharging, and a series of global models are developed for the discharge in the boundary gas layer adjacent to the water surface. The interfacial distributions of reactive species and their fluxes onto the water surface are quantified. It is found that the electron density is 10¹⁶-10¹⁷ m⁻³ and it shows an annular distribution in the boundary gas layer. The density distributions of most reactive species there reveal ring-like shapes as well. The dominant cation and anion in such a boundary layer are H₃O⁺ and OH⁻, respectively. The most abundant metastable is O₂(a¹Δ), the most abundant reactive oxygen species are H₂O₂ and OH, and the most abundant reactive nitrogen species are NO and HNO₂. The species of H₂O₂, OH, HO₂, and HNO₂ are reportedly to have significant biological effects, and in our simulation, their fluxes onto the water surface are remarkable, higher than 10¹⁷ m⁻² s⁻¹. In addition, the effects of radial gas velocity and water evaporation on the particle flux distributions are also revealed.