Particle-in-cell/Monte Carlo collisional simulation of negative streamer formation and branching between planar electrodes

In this paper, the mechanism of negative streamer formation and branching between planar electrodes is studied using a two dimensional particle-in-cell/Monte Carlo collisional model. Super-particles, each one of which represents many physical particles, are used in our model to reduce the calculation and memory usage. The electric field applied to the gap between electrodes is constant and is above the breakdown value already before the streamer formation. For nitrogen at standard temperature and pressure, the simulation is first performed in the background field of 10 MV/m. The results show that prior to branching, the streamer head is flattened, and the non-uniform distribution of electrons accelerated to energies above 50 eV is obtained at the flat streamer head, which then leads to streamer branching. Then, additional simulations in the background fields of 9 MV/m, 11 MV/m, and 12 MV/m are performed to investigate the effects of background field. The results show that the streamer propagates faster, has larger plasma density, and branches more rapidly in a stronger field. The simulation results of argon are also given at a standard temperature and pressure in the background field of 10 MV/m. The results show that more branches can be obtained in argon compared with nitrogen, which agrees well with the experimental results.