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

Abstract

Streamer-to-filament transition is a general feature of nanosecond discharges at elevated pressure. The transition is observed in different discharges by different groups: in the nanosecond surface dielectric barrier discharges (nSDBDs) in a single shot regime at high pressure (2-15 bar), in the point-to-point or point-to-plane open electrodes discharges at high repetitive frequency (so-called nanosecond repetitive pulsed discharges, NRPDs) at atmospherics pressure. The present paper contains experimental analysis of plasma properties in the filamentary nSDBD: the electrical current, the specific deposited energy, the electron density and the electron temperature were measured for a wide range of pressures and voltages. A model explaining plasma properties in filamentary nanosecond discharges and the role of excited species in streamer-to-filament transition is suggested and discussed.

Filamentary nanosecond surface dielectric barrier discharge. Experimental comparison of the streamer-to-filament transition for positive and negative polarities

“…It was suggested [26] that such a slow decay of the electron density is due to fact that plasma in the filaments is close to local thermal equilibrium (LTE); the gas temperature in the discharge is a few electronvolts, and the dynamics of plasma decay is determined mainly by gas cooling. This idea is developing in [27], where a kinetic model is suggested to provide a sharp, parts of nanoseconds, transition from streamer to filamentary plasma. Analysis of surface charge per streamer and per filament shows that for both polarities, the charge per filament accumulated on the surface is at least one order of magnitude higher than the charge per streamer [28].…”

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

“…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]. The authors demonstrated that the increase of pressure can be responsible for the transition from a weakly ionized plasma (called "streamer") to a fully-ionized plasma (called "filament").…”

“…This was already seen when the excited states of molecular nitrogen were included in Ref. [21]. New simulations are performed changing the number of nitrogen and oxygen excited states included in the chemical mechanism.…”

“…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').…”

“…The cross-sections of electron reactions are used to calculate the corresponding reaction rates and are taken mostly from the LXCat database [33][34][35][36]. Because excited states of molecular nitrogen can play a role in the ionization process [21], the ionization cross-sections of N 2 * are added, based on the work of Bacri and Medani [37]. The aim of this work being to simulate a fully ionized plasma, the ionization of atomic species and their reverse process must be included.…”