Particle-in-cell simulation of corona discharge in low pressure in stepped impedance transformer

The corona discharge process in low pressure N2 in stepped impedance transformer (SIT) is simulated using 3-D particle-in-cell (PIC) software (VORPAL). The evolution of the charged particle spatial distribution during the discharge is obtained. The two main discharge mechanisms, i.e., multipactor and corona discharge, are analyzed. From the simulation results, it can be found that the threshold voltage of breakdown of the SIT first decreases and then increases. In addition, with the increase of the pressure, the multipactor effect weakens while the corona discharge effect strengthens. Through the comparison of the threshold voltages between two kinds of wall materials, i.e., Ag and Cu, the critical pressures between the two discharge mechanisms are achieved.