Effects of SF6 mixing ratio on DC positive streamer propagation in SF6/N2 gas discharge under a nonuniform electric field

The determination of the low-temperature plasma propagation of SF6/N2 in gas discharge will accelerate the application of SF6/N2 in advanced electrical equipment. This study investigates the positive streamer propagation characteristics of SF6/N2 by establishing a plasma discharge model and discusses the effects of SF6 ratio on the electron density, electric field, chemical reaction rates, ion concentrations, and streamer thickness and velocity. As the streamer propagates, the shapes of the electron density and electric field become “narrower and taller.” Moreover, the ionization and attachment reaction rates increase, and the streamer thickness and velocity decrease with increasing SF6 mixing ratio and propagation time. As the SF6 ratio increases, the electric field distortion degree and particle mobility near the high-voltage electrode decrease due to the increase in the ionization and attachment rates. Consequently, the streamer velocity remains nearly unchanged, but the streamer thickness obviously decreases in the corona discharge process. In the streamer propagation process, the decrease in the streamer thickness and velocity with increasing SF6 ratio is attributed to the reduction in the electric field distortion and particle mobility, which stems from the increase in the DC breakdown voltage with the SF6 mixing ratio. The study results clarify the influence mechanisms of the SF6 mixing ratio on the particles’ spatiotemporal evolution during streamer propagation.