Positive and negative streamers in ambient air: modelling evolution and velocities

Abstract

Abstract. We simulate short positive and negative streamers in air at standard temperature and pressure. They evolve in homogeneous electric fields or emerge from needle electrodes with voltages of 10 to 20 kV. The streamer velocity at given streamer length depends only weakly on the initial ionization seed, except in the case of negative streamers in homogeneous fields. We characterize the streamers by length, head radius, head charge and field enhancement. We show that the velocity of positive streamers is mainly determined by their radius and in quantitative agreement with recent experimental results both for radius and velocity. The velocity of negative streamers is dominated by electron drift in the enhanced field; in the low local fields of the present simulations, it is little influenced by photo-ionization. Though negative streamer fronts always move at least with the electron drift velocity in the local field, this drift motion broadens the streamer head, decreases the field enhancement and ultimately leads to slower propagation or even extinction of the negative streamer. Positive and negative streamers in ambient air: modeling evolution and velocities 2

Positive and negative streamers in ambient air: measuring diameter, velocity and dissipated energy

“…Theoretical investigations of the difference between positive and negative streamers in three spatial dimensions (using the cylindrical symmetry of a streamer to calculate effectively in the two dimensions r and z) and including the photo-ionization effect in air are quite rare [37,38,39,40], a thorough discussion and new results that closely correspond to the experimental results of the present paper are presented in [41].…”

Probing photo-ionization: simulations of positive streamers in varying N2 : O2-mixtures

“…Despite the fact that positive streamers propagate against the electron drift velocity, in air they appear more easily than negative streamers and they propagate faster. This faster propagation was observed in experiments [9] and explained in [10]: in negative streamers, the electrons at the side of the streamer channel drift outwards and reduce the field focussing at the streamer tip while positive streamers stay narrow and therefore enhance the electric field at the streamer tip to higher values.…”

“…Different grids with different refined areas are used for the particle densities and for the electric field. The needle electrode is modeled by a floating point charge using a "charge simulation technique" as described in [10], and earlier in [39]. The computational domain of the density equations starts at the tip of the needle electrode and extends towards the planar electrode, depicted by the shaded area in figure 2.…”

Unstable Leader Inception Criteria of Atmospheric Discharges

“…All phases of the streamer propagation are calculated by solving the continuity equations coupled with Poisson's equation. In order to calculate the streamer propagation over long gaps for a long period of time, two-dimensional forms of the continuity equations have been used [28,29]. Streamers and the stem of the channel are assumed to occupy a narrow cylindrical channel.…”