Numerical study on the discharge pattern evolution in an atmospheric pressure helium dielectric barrier discharge under the variation of nitrogen admixture content

Abstract

We report a systematic numerical study concerning the effect of traces of nitrogen admixtures on the discharge pattern dynamics in an atmospheric helium dielectric barrier discharge. By gradually increasing the N2 concentration from 1 to 1000 ppm, the discharge mode transformed from the stationary pattern, via quasi-uniform structure, stationary pattern, into the complementary pattern. Analyses revealed that Penning ionization exerted a significant influence on the electron distribution, surface charge deposition and electric field profile over the gap and thus induced the transitions in pattern structure. With the increase of N2 content, the average rate of Penning ionization within the afterglow stage presented a non-monotonic variation trend, which conformed to previous results, and seed electron level of the main discharge varied in a similar way. When the discharge was ignited with a large amount of seed electrons, the electron distribution prior to the breakdown phase tended to homogenize and the level of radial electric field during the pre-ionization process was restrained, contributing to the homogenization of the discharge. Furthermore, the formation of complementary discharge pattern was believed to be resulted from the excessive reduction of average electron density between two adjacent main discharges at above 500 ppm N2 level. The reduced electron concentration made the volume ionization more susceptible to the surface charge distribution and led to the disruption of discharge channel succession between positive and negative half cycles.