Investigation of positive streamers by double-pulse experiments, effects of repetition rate and gas mixture

Abstract

Streamer discharges are often operated in a repetitively pulsed mode and are therefore influenced by species left over from the previous discharge, especially free electrons and ions. We have investigated these effects by applying two consecutive positive high voltage pulses of 200-700 ns duration to a point-plane gap in artificial air, pure nitrogen, other nitrogen-oxygen mixtures and pure argon at pressures between 67 and 533 mbar. The pulses had pulse-to-pulse intervals ( t) between 200 ns and 40 ms. We imaged both discharges with two ICCD cameras and combined this to a compound image. We observe for values of t below 0.5-15 µs (at 133 mbar, with t depending on gas mixture) that during the second pulse the streamers continue the paths of the first-pulse streamers. We call the maximal time for which this continuation still occurs the continuation time. For N 2 -O 2 mixtures, this time has a maximum at an oxygen concentration of about 0.2%. According to our plasma-chemical modelling this maximum is determined by the electron loss rate which has a minimum around this oxygen concentration. Depending on oxygen concentration the dominant recombining positive ion is N + 4 , O + 2 or O + 4 where O + 2 dominates around 0.2% O 2 and recombines slowest. For increasing values of t we observe that after the continuation phase first no new streamers occur at all, then new streamers show up that avoid the entire pre-ionized region. Next we see new thin streamers that follow the edges of the old channels. For larger t (10-200 µs) the new streamers start to increase in size and move to the centre of the old channels. Finally, around millisecond timescales the new channels are completely independent of the old channels.Together this points to the combination of two mechanisms: streamers search the proximity of regions with increased electron density, but cannot penetrate regions with very high electron density.

Breakdown features of a high-voltage nanosecond discharge initiated with runaway electrons at subnanosecond voltage pulse rise time

“…Currently the studies of formation and propagation of streamer at breakdown of elevated pressure gases are conducted actively [17][18][19][20][21][22][23][24][25]. The streamer propagation velocity was shown to increase with applied voltage [17][18][19].…”

“…3D particle simulations included a natural level of background ionization in the form of positive and O 2 − ions. In [23] streamer discharge operated at applying two consecutive positive highvoltage pulses to a point-plane gas-filled gap was investigated. The appearance of runaway electrons during streamer propagation was discussed in [24,25].…”

Modeling and Identification of Electrical Parameters of Positive DC Point-to-Plane Corona Discharge in Dry Air Using RLS Method

“…The equivalent interelectrode resistance gradually recovers the initial value after the relaxation phase of the discharge current, which extends up to a few hundreds of nanoseconds. In the channel of a corona discharge, the conductivity is proportional to the electron density [31], [32]. During its propagation toward the cathode and due to the rapid growth of space charge in the head of streamer, the number of ionizations increases proportionally and even the number of electrons.…”

Electrical Modelling of a Positive Point to Plane Corona Discharge at Atmospheric Pressure

“…In the channel of a corona discharge, the conductivity is proportional to the electron density [21,22]. The equivalent inter-electrode resistance gradually recovers the initial value after the relaxation phase of the discharge current which extends up to a few hundred nanoseconds.…”