Development of nanosecond discharges in atmospheric pressure air: two competing mechanisms of precursor electrons production

In this paper, we present the results from the computational study of the two competing mechanisms of precursor electrons production-conventional photoionization and preionization by fast electrons from the cathode. To discriminate between the two mechanisms we simulate a negative streamer evolution under conditions when photoionization is zero/ non-zero and/or fast electrons are present/absent. In the absence of all factors producing the precursor electrons the streamer eventually stalls. We show that the effect of fast electrons on streamer evolution is similar to that of the photoionization but it is more stochastic by nature. The domination of one or another of the mechanisms considered depends on the pulse duration and voltage amplitude (other conditions being equal).