Influence of nitrogen impurities on the performance of multiple-current-pulse behavior in a homogeneous helium dielectric-barrier discharge at atmospheric pressure

A systematic investigation regarding the influence of nitrogen impurities on the evolution of multiple-current-pulse (MCP) behavior in a homogeneous dielectric-barrier discharge is carried out via fluid modelling. By gradually up-regulating the N-2 content from 0.1 ppm to 10 000 ppm, the discharge evolves from MCP mode into a single-pulse mode, and finally returns to MCP mode. Analyses reveal that Penning ionization plays an important role in regulating the MCP performance. Under 10 ppm nitrogen content, the direct electron impact ionization predominates the total ionization process while Penning ionization is negligible. A relatively low pre-ionization level and seed electron level of incipient pulse (n(e0)) in this stage induce a strong incipient current pulse as well as MCP. As N-2 content increases, the pre-ionization level and n(e0) are enhanced due to the elevation of Penning ionization rate, leading to the smoothing of gap voltage profile and the annihilation of MCP at 10 ppm. Above 100 ppm, Penning ionization becomes the dominant ionization channel. As N-2 content exceeds 300 ppm, the MCP reappears, which is believed to be resulted from a slump in metastable density owing to the excessive dissipation by Penning ionization. Beyond 1000 ppm, the strengthening of glow discharge structure at the incipient current peak phase contributes to the further increase of J(pm) as well as pulse number.