Effects of oxygen concentration on helium-oxygen dielectric barrier discharges: From multi-breakdowns to single-breakdown per half-cycle

In this paper, a one-dimensional fluid model of He + O₂ dielectric barrier discharge is established. As the oxygen concentration increases from 0.2% to 0.7% and 1.2%, the plasma transforms from triple-breakdowns to single-breakdown per half-cycle. In the mode of multi-breakdowns, the first pulse produces more particles although dissipates more power, thus making remarkable differences in the energy efficiencies in producing charged species but can hardly affect neutral species. We also operate the model in another way that the plasma is held in the mode of single-breakdown, by changing the oxygen concentration and voltage amplitude at the same time, so the impact of mode transformation is removed. In this way, the production efficiency of the electron decreases significantly, probably owing to the enhanced electron attachment with O₂ and O₃. After analyzing the main chemistry process of both charged and neutral species, it is suggested that the decreasing efficiency of the electron and the increasing oxygen concentration impose opposite impacts on the energy efficiencies of other species. Almost all charged species decrease more or less in their efficiencies, but O₃ ^- is the exception. For neutral species, the efficiencies vary slightly for O and O^∗ but increase more than 250% for O₂ ^∗ and O₃.