Simulation of positive streamers in CO₂ and in air: the role of photoionization or other electron sources

Abstract

Positive streamer discharges have been studied and modelled extensively in air. Here we study positive streamers in CO 2 with and without oxygen admixtures; they are relevant for current high voltage technology as well as for discharges in the atmosphere of Venus. We discuss that no ef cient photoionization mechanism is known for gases with a large CO 2 fraction, as photons in the relevant energy range are rapidly absorbed. Hence positive streamers can propagate only due to some other source of free electrons ahead of the ionization front. Therefore we study positive streamer propagation in CO 2 with different levels of background ionization to provide these free electrons. The effect of replacing photoionization by background ionization is studied with simulations in air. Simulating streamers in background elds of 16 to 20 kV cm −1 at standard temperature and pressure within a gap of 6.4 cm, we nd that streamer propagation is rather insensitive to the level of photoionization or background ionization. We also discuss that the results depend not only on the value of breakdown eld and applied electric eld, and on preionization or photoionization, but also on the electron mobility µ(E) and the effective ionization coef cient α eff (E), that are gas-dependent functions of the electron energy or the electric eld.

Comparing simulations and experiments of positive streamers in air: steps toward model validation

“…In previous computational studies, an elongated ionized seed with an equal density of electrons and positive ions was often used as a pseudo-electrode to start a streamer, see e.g. [13,52]. Due to electron drift such a seed becomes electrically screened, leading to a high electric field at its tip that can start a streamer discharge, depending on the shape and density of the seed [37].…”

“…For the simulations, we use a drift-diffusionreaction type fluid model with the local field approximation, as described in section 2. This model is commonly used to simulate streamer discharges [12,13,14], and the aim of the present paper is to take steps towards its validation. To understand how reliable simulations are, we first study the deviation between experimental and simulation results in section 3.…”

3D particle simulations of positive air-methane streamers for combustion

“…The properties of streamers are determined by the electron dynamics which, in turn, are governed by gas-specific photoionization and swarm parameters. There are numerous investigations on streamers in different gases which illustrate this gas-dependency, for example: CO 2 [5], N 2 :CH 4 [6], air with artificially increased electron attachment or reduced photoionization [7,8] and N 2 -O 2 mixtures in various ratios [9,10].…”

Investigating CO$_{2}$ streamer inception in repetitive pulsed discharges

“…According to equation 1, the time that The electric field on the symmetry axis as a function of distance for the first 20 mm from the tip for V HV = 10 kV and V LV = 1 kV. The breakdown electric field (dashed line) is 0.66 kV/mm at 300 mbar and is taken from Bagheri et al [19].…”