The Sliding Discharge Phase of a Plasma Focus

An electromagnetic particle-in-cell (EMPIC) code was developed to numerically study the early breakdown phase of the United Nations University - International Centre for Theoretical Physics (UNU–ICTP) plasma focus (PF) device prior to the electrical breakdown. The formation and propagation of the sliding discharge on the insulator surface were simulated. The analysis of the electric field near the insulator surface and the surface charges showed that the field distribution was predominantly attributed to these charges accumulated over time, when the plasma electrons strike the surface. From the electron density distribution at various times, the electron density profile was found to propagate with a constant velocity. Based on the computed Townsend ionization coefficient, the sliding discharge velocity was estimated to be $4.5 \times 10^{6}$ m/s, a value that is consistent with a fast ionization wave.