Modeling of plasma formation and expansion in a high-voltage anode-cathode gap*

Plasma formation and expansion play an important role in pulsed power systems, such as high-power microwaves (HPMs) and magnetically-insulated transmission lines for Z pinch. For instance, explosive electron emission with dielectric cathodes, such as carbon velvet[1], has been used in HPMs. However, the plasma expansion in the high-voltage anode-cathode gap causes impedance collapse resulting in pulse shortening. To advance our understanding of plasma formation and expansion, self-consistent modeling is required including field emission, surface flashover, and particle interactions (ionization, excitation, Coulomb, and elastic collisions). A one-dimensional relativistic particle-in-cell (PIC) Monte Carlo Collision (MCC) simulation model is used to study the evolution of cathode plasma dynamics during a voltage pulse in a velvet cathode. The effect of important parameters such as the outgassed neutral layer (type of gas, density), pulse waveform, and field-enhancement factor are investigated.

[1] R. B. Miller. Mechanism of explosive electron emission for dielectric fiber (velvet) cathodes. Journal of Applied Physics, 84(7):3880–3889, 10 1998