The effects of field-enhancement factor on the nanosecond pulsed breakdown of nitrogen spark switch at atmospheric pressure with 3D PIC-MCC model

It is necessary to study the mechanism of the effects of discharge parameters on the breakdown process of the gas spark switches under pulse voltages with a rise time of tens of nanoseconds. In this paper, the effects of field-enhancement factor on the nanosecond pulsed breakdown of the nitrogen spark switch at atmospheric pressure are investigated. Based on the field emission assumption, the simulations are carried out using a three-dimensional particle-in-cell, Monte Carlo-collision model with a field-enhancement factor of 500 and 1000, respectively, when the pulse voltage rise time is 65 ns. The results can be summarized as follows. First, the discharge process mainly consists of the electron avalanche formation and the streamer development. For the different field-enhancement factors, the electron avalanches all propagate towards the anode, while the streamer simultaneously all develop towards both the anode and cathode. Second, the branches exhibit in the discharge channel during the streamer phase. On the one hand, the different ionization rates caused by the heterogeneous distribution of electron energy result in branches appearing at the head of the streamer. On the other hand, the initial streamer continuously combines with the secondary electron avalanches and streamers generated by photoionization, which leads to branches at the tail of the streamer. Finally, the significant pre-ionization effect can be realized with a higher field-enhancement factor to effectively promote the steady generation and propagation of streamer, while minimizing the bifurcation phenomenon of streamer channel. In this case, the breakdown jitter of gas switches can be minimized by enhancing the cathode surface roughness.