Effect of trace oxygen on self-oscillation of positive glow corona in nitrogen near atmospheric pressure

Positive glow corona is a stable and quasi-homogenous form of corona discharge with periodic current pulses, which appears in atmospheric plasma applications, high voltage apparatus and grounded structures under thunderstorm. The debate on seed electron source responsible for pulsing nature of positive glow corona has persisted for decades. This paper presents the numerical simulation study of 1-D coaxial positive glow corona in pure N2 with trace oxygen contents ranging from 1% to 1 ppm. It is found that the reduction of oxygen content causes weaker glow current magnitude, longer time-to-crest, shorter oscillation period and more positive ion sheaths. As trace oxygen decreases from 1% to 10 ppm, the dominant source of secondary electrons transits from both detachment and photoionization to photoionization only. As trace O2 content drops from 0.1%, the dominant photoionization within ionization layer transits from the photoionization of O2 molecules to direct photoionization of N2 molecules. In high purity nitrogen, the detachment of O− dominates and the detachment of O2− can be neglected. As the trace oxygen decreases from 1% to 10 ppm, the dominant molecules involving O− detachment transits from N2 and O to N2(A). The dominant ionization responsible for electron multiplication during electric field recovery shifts from direct ionization of O2 and N2 in 1% trace oxygen to associative ionization between N2(A) and N2(a’) and direct ionization of N2 in 1ppm trace oxygen.