2D PIC-DSMC simulation of microscale breakdown after vacuum seal failure

Summary form only given. An electrostatic particle-in-cell code with complex boundary conditions and direct simulation Monte Carlo particle collisions performed on a separate, adaptable collision mesh is utilized to investigate DC breakdown after vacuum failure. Previously, it has been found that cold field electron emission can explain the breakdown voltage deviation from the Paschen curve measured for small gaps. Furthermore, prior 1D simulations found that breakdown was sensitive to a fixed non-uniform background neutral gas distribution across the gap and that if the gap size is of order the mean free path then gas concentrated near the anode results in smaller breakdown voltages because electrons reaching the anode have energies near the peak of the ionization cross section. In the present work the two electrodes are separated by a vacuum gap and air at atmospheric pressure is allowed to flow into the gap from either the anode or cathode due to a small “crack” in the electrode resulting in a non-uniform neutral gas distribution. The simulation includes Auger neutralization, cold field emission (CFE) of electrons, electron-neutral elastic, ionization, and excitation interactions and ion-neutral interactions including charge exchange. The simulated breakdown voltages at various electrode gap sizes are compared to the Paschen curve and breakdown is found to be sensitive to the neutral gas density distribution as it develops across the gap from either the cathode or anode leak.