The propagation of positive streamers in a weak and uniformbackground electric field

Abstract

Theresults of numerical simulations of a positive streamer development in airin a weak and uniform electric field are presented. Streamer dynamics isconsidered in an electrode gap of 33 mm in length and the configurationwas `protrusion on a plate-plate'. This particular configuration waschosen in order to perform direct comparison between simulated results andexperimental data. The electrostatic field in such a system decreasesrapidly with increase of the distance from the protrusion (anode) and theregion with a weak and uniform background field covers ~30 mm of thegap. The parameters of the propagating streamer are studied at sixdifferent values of the background field strength: 0.24; 0.30; 0.345;0.37; 0.43 and 0.50 MV m-1. Stable streamer development (withconstant velocity) takes place in a field of 0.5 MV m-1 (thestability field) but the streamer is able to cross the gap in a backgroundfield of 0.3 MV m-1. These values are in excellent agreement withexperimental data. During the stable streamer propagation, the electrondensity and plasma conductivity in the discharge channel and the electricfield at its front remain constant. In a background field lower than0.5 MV m-1, the discharge front velocity and the electric field atthe front decrease linearly with an increase of streamer length. Thedischarge propagation in the stability field is associated with anincrease of electrostatic energy at the streamer front but it decreases ifthe streamer develops in a weaker electric field. This behaviour isaccompanied by a constant Joule dissipation at 0.5 MV m-1 anddecreasing energy losses at the streamer front in a weaker backgroundelectric field.