Modeling high-voltage DC breakdown for single- and multi-stack insulators

Summary form only given. This work reports on 2D Particle-In-Cell (PIC) simulations of DC breakdown in high-voltage systems with monolithic or multi-stack dielectric insulation. The focus of this work is to characterize and order the various contributions to breakdown, starting with multipactor in DC applied fields. Simulations use a simple Bergeron geometry similar to that in Ref.. A modified form of the PIC model developed by Taverniers, et al., is used, adding parameters for increased spatial resolution to study near-surface phenomena while maintaining reduced grid errors. Models for space charge, dielectric charging, and secondary-emission are included. Parameters include insulator angle, gap width, applied voltage, and various parameters for secondary-emission. Initial simulation studies report on DC multipactor breakdown initiated near a triple-point current source. Emission models include a constant-amplitude current source, a Fowler-Nordheim current source, and a triple-point source adapted from Schachter´s theoretical model. Breakdown is declared when a current has reached the anode. In the absence of reflected and scattered primaries (SRP), electron growth by multipactor is compounded with surface charging. Primary electrons from the current source can multiply upon impact on the dielectric if their energy is between the first and second crossover energies; secondary electrons can further multiply under the same criterion, hence multipactor. However, due to the low emission energies of true secondaries, significant surface charge is required to advance total electron growth in the absence of SRP. Inclusion of SRP leads to distributed charging across the dielectric that can influence multipactor growth. Breakdown voltage, with and without SRP, as a function of angle is presented and compared. Characteristic system behavior with respect to current-source type will be discussed. Effects of higher spatial resolution near the dielectric surface to properly sa- ple early space-charge effects in simulation will be presented. Finally, initial studies of multi-stack models with finite-thickness electrodes will be presented and discussed.