Numerical study on helium-oxygen dielectric barrier discharges: From single-breakdown to multi-breakdowns per half-cycle

Helium-oxygen dielectric barrier discharge has received much attention due to its high efficiency and stability in producing reactive oxygen species (ROS). Previous studies evidenced that the dielectric-barrier controlled plasma would transform from single-breakdown to multi-breakdowns per half cycle with the increasing applied voltage, but the variation of densities and wall fluxes of ROS during the transformation has not been well understood. This motivates us to construct a one-dimensional fluid model for this study. The results show that the volume-averaged densities and wall fluxes of the electron, ions, and atomic metastables are temporally pulsed with each breakdown, but they are nearly invariable for the grounded neutrals (O and O₃) and molecular metastables [such as O₂(a¹Δ_g)]. For each species, the temporal pulses of density and flux of a specific species have different widths, and the widths remain almost constant in time among the breakdowns except for that of the electron. With the increasing number of breakdowns per half cycle, the wall fluence and the peak value of temporal flux pulses of O⁻ have obviously different trends, and the energy efficiencies for the production and wall fluence increase significantly only for O⁻ and O₃ ⁻.