On the arc transition mechanism in nanosecond air discharges

Abstract

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Filamentary nanosecond surface dielectric barrier discharge. Plasma properties in the filaments

“…The authors [33] remark that the nature of the observed electron cloud is still under discussion and mention the field emission in strong electric field and a possibility of production of a supercritical fluid during explosive heating of a single spike or multiple spikes on the cathode. Non-numerous experimental observations [11,13,14,37] obtained in mm or sub-mm pin-to-pin gaps report the start of the filament from the cathode, then, with a delay of the order of 1 ns -from the anode, and then the filaments merge in the middle of the gap [13,37]. Significant decrease of the streamer radius, by a factor of 3 − 5, on the time scale 0.5 ns before the filamentation is recently reported [13].…”

“…Non-numerous experimental observations [11,13,14,37] obtained in mm or sub-mm pin-to-pin gaps report the start of the filament from the cathode, then, with a delay of the order of 1 ns -from the anode, and then the filaments merge in the middle of the gap [13,37]. Significant decrease of the streamer radius, by a factor of 3 − 5, on the time scale 0.5 ns before the filamentation is recently reported [13]. Significant changes of parameters of the streamer plasma in the radial direction before the filamentation were observed in [14]: significant increase of gas temperature in the middle of the channel was measured; significant, 5-6 times, decrease of radius was reported.…”

“…The decay of the electron density was slow, a few tens of nanoseconds. Later experimental observations of nanosecond repetitive plasma (NRP) at atmospheric pressure [11][12][13] also report densities of electrons on the level n e ∼ 10 18 − 10 19 cm −3 , constriction of the discharge channel, high electron temperatures reaching a few electronvolts and slow plasma decay, tens of nanoseconds. The authors of [14] measured the ultra-fast gas heating observed by optical emission spectroscopy on the axis of the streamer before the constriction of the channel.…”

Role of the excited electronic states in the ionization of ambient air by a nanosecond discharge

“…This mechanism explains in our opinion the fast transition (< 1 ns) from a non-equilibrium to a thermal plasma as experimentally observed with nanosecond discharges in Refs. [17,21,43]. Ionization rates of N2(X, A, B, C, a').…”

“…Stark broadening was also used for electron number density measurement in several works in pin-to-pin or pinto-plane configuration [16][17][18][19] and all authors reported electron number densities higher than 10 18 cm -3 . Such a high electron number density was also reported in SDBD discharges [20][21][22].…”