Influence of Oxygen on the Multiple-Current-Pulse Behavior in an Atmospheric Homogeneous Helium Dielectric Barrier Discharge With Air Impurities

In this paper, through a one-dimensional fluid model, we investigate the influence of oxygen on the multiple-current-pulse (MCP) behavior in an atmospheric homogeneous dielectric barrier discharge (HDBD) in helium with air impurities. From the simulation results, we find that the O2 Penning ionization plays a leading role in the discharge characteristics. As the air content increases from 0 ppm to 5000 ppm, the current waveforms show a transition from a single-pulse mode to MCP mode, and the number of current pulses ( $N_{\mathrm {p}}$ ) also increases. Through analysis, we find that although $N_{\mathrm {p}}$ increases monotonically, the evolution mechanism of the MCP discharges under different ranges of air content is different. At lower air concentration (less than 500 ppm here), we find the similar explanation as that reported in our previous work on the MCP behavior only considering N2 impurity. However, when the air content is higher, we find that the seed electron density ( $n_{\mathrm {e0}}$ ) remains basically unchanged, not like the sharp drop at lower air concentration. Further analysis reveals that the rapid growth of direct ionization during a small period before the breakdown helps generate MCP discharges. In addition, the attachment reaction of O2 is analyzed. Results show that at higher air content (above 5000 ppm here), the O2 attachment reaction will provide more possibilities of successive ignitions after the first pulse with the assistance of the applied voltage, implying a stimulative effect of the oxygen on MCP discharges.