Effect of inhomogeneities on streamer propagation: I. Intersection with isolated bubbles and particles

Abstract

The branching of streamers in high pressure gas discharges and discharges in liquids is an almost universal occurrence having many causes. In this paper, we discuss results of an investigation of one possible cause-inhomogeneities in the media through which the streamer propagates. These inhomogeneities produce corresponding enhancements or decreases in ionization and excitation as the avalanche front encounters them, some of which may produce branching. Three types of inhomogeneities were investigated-negative bubbles (regions having a lower density than ambient), positive bubbles (having a higher density) and solid bubbles (particles). Depending on the size and density of the bubble, the streamer can be focused into the bubble (negative small bubble), deflected and split (positive bubbles and particles) or refracted (large negative bubble). In the case of gaseous bubbles, this behavior is partly explained by the larger E/N (electric field/gas number density) in the negative bubble, producing more ionization by electron avalanche, and smaller E/N in the positive bubble, producing less ionization. A streamer may diverge into a negative bubble located off axis due to seeding of electrons in the bubble by photoionization and subsequent avalanching in the large E/N.

Three-dimensional numerical modelling of gas discharges at atmospheric pressure incorporating photoionization phenomena

“…According to the literature at least four causes are involved in streamer branching: Laplacian instabilities [7], pressure instabilities [6], streamer interactions [25] and photoionisation fluctuations [26]. Here we consider the effect of plasma spots and low pressure instabilities (bubbles in [6]) on streamer propagation. Plasma spots usually have a spherical form with a radius of several micrometers and a charge density within them that resembles a Gaussian distribution.…”

“…In this work the effect of (i) the distance between the plasma spot and the streamer, (ii) the size of the plasma spot and (iii) the charge density in the plasma spot on streamer propagation is considered. Low pressure instabilities, on the other hand, can appear in the discharge volume in a chaotic way [6]. The magnitude of these fluctuations is dependent on the external conditions of the discharge and is expected to be more significant in the atmosphere (e.g.…”

“…The drift velocity of the electrons is also higher in the bubble than outside. As a result, the streamer accelerates into the bubble [6] (see Figure 15). In Figures 15(a), 15(b) and 15(c) the effect on streamer propagation of the bubble pressure and the distance between the bubble and the streamer head is shown.…”

“…Two-dimensional axi-symmetric models are predominantly employed allowing the study of some phenomena in a three-dimensional setting as well. Work based on 1.5D and 2D models [6][7][8] has been conducted by making several assumptions in an attempt to understand several aspects of streamer branching and streamer interaction. However, one important drawback of the 2D axi-symmetric models is that they restrict gas discharge modelling in configurations and conditions that are inherently symmetric around the axis of symmetry.…”

Simulation of the discharge propagation in a capillary tube in air at atmospheric pressure

“…In the work of Sobota et al [2009] in Argon, for ε r varying between 2.3 − 4.5 and 9.1, a very small influence of the surface discharge velocity is observed. Babaeva et al [Babaeva et al, 2006;Babaeva and Kushner , 2009] studied the influence of dielectric dust particles on the discharge structure in air at atmospheric pressure. They showed that streamers encountering a particle could branch or initiate new streamers depending on the permittivity and size of the particles.…”