Burst pulses and secondary streamers from positive points

We present numerical results that provide an explanation of the occurrence of burst pulses and secondary streamers at intervals of 10–20 μs after a positive onset corona streamer pulse in air at atmospheric pressure. The calculations show that the positive charge left in the streamer channel, after a primary streamer has stopped, before reaching the cathode, will move away from the point causing a rising electric field at the anode. After 10 μs, this electric field is high enough, over a sufficient distance, that the conditions become suitable for a self-sustained discharge, and seed electrons near the anode cause a rapid increase in charge density. A secondary streamer then forms at the anode and propagates along the length of the original streamer channel in ∼300 ns, stopping at the same point as the primary streamer. The amplitude of the secondary current pulse is ∼10% of that of the primary current pulse. After each pulse, the remnant positive charge moves away from the point, creating the necessary conditions for further pulses; thus a series of pulses can be formed. The time between pulses is governed by the movement of the remnant positive charge away from the point. The remnant positive space-charge limits the size of the burst pulses which are considerably smaller than the primary pulse.