Impedance collapse in a high-voltage diode due to anode and cathode plasma formation and expansion

It is known that plasma formation and expansion from the anode and cathode surface leads to impedence collapse in pulsed power systems. As these systems operate at higher applied voltages up to megavolts (MV), a self-consistent plasma simulation model is required to understand the plasma dynamics. A relativistic, one-dimensional, particle-in-cell (PIC) Monte Carlo Collision (MCC) simulation is developed to model the plasma dynamics in the anode-cathode gap by including physical processes such as field emission from cathode, thermal and stimulated desorption of neutrals from the anode, electron-neutral collisions, and electron-electron/ion Coulomb collisions. The grid-based Langevin method is revisited and implemented for modeling Coulomb collisions, and the null-collision MCC algorithm models electron-neutral elastic, excitation, and ionization processes. The simulation grid size and time steps resolve the Debye length and the plasma frequency, resulting in over 24000 cells in a 1 cm anode-cathode gap. The plasma expansion speed from the present simulation agrees well with experimental results from the literature. We will also discuss the mechanism of current bursts observed in high-voltage anode-cathode gaps and the modeling of anode plasma formation.