Modeling of electrode plasma formation and expansion in pulsed power systems

Electrode plasmas in pulsed power systems cause impedance collapse due to gap closure and material degradation during repeated pulses. A self-consistent one-dimensional relativistic particle-in-cell Monte Carlo collision (PIC-MCC) model, originally developed to study cathode plasma formation in a high-voltage anode-cathode (AK) gap[1], is extended to include a model for anode temperature and neutral desorption rates. The kinetic modeling results show that during the initial phase of the pulse, cathode plasma forms, resulting in a monopolar space charge limited (SCL) current in the AK gap. Next, the intense relativistic electron beam heats the anode, leading to exponential thermal desorption of neutrals once its temperature exceeds a threshold value. Anode plasma forms due to the ionization of desorbed neutrals, which transitions the SCL flow from monopolar to bipolar, increasing the net current collected at the anode. Results will be presented on the plasma dynamics and the current characteristics in the diode, which depend on electrode plasma expansion and the transition from monopolar to bipolar SCL flow.

[1] V. Sharma, Y. Yamashita, and K. Hara, “Kinetic modeling of cathode plasma formation and expansion in a pulsed high-voltage anode-cathode gap,” Journal of Applied Physics, (in press) 2025.