Characteristics of gaseous breakdown in DC for dielectric-loaded systems

Summary form only given. This work reports on 2D Particle-In-Cell (PIC) simulations of gaseous DC breakdown from vacuum through atmospheric pressure in dielectric-loaded, high-voltage systems. The focus of this work is to characterize and order various contributions to breakdown, starting with single-surface multipactor in DC. Simulations use a simple Bergeron geometry similar to that in [1] with a modified PIC model from [2]. Models for space charge, dielectric charging, and secondary emission [3] are included. Seed-current emission models include constant-amplitude source, a Fowler-Nordheim source, and a theoretical triple-point source adapted from [4]. Breakdown is declared when a multiplicative current has reached the anode. Parameters include insulator angle, gap width, applied voltage, seed-current amplitude and type, various parameters for secondary emission, with target gases of argon and air. In the case of a constant-amplitude, beam-like seed, vacuum DC breakdown is typically characterized by a multipactor front resulting from saturated dielectric-surface fields in the wake of the front; a short-lived, catastrophic anodic current develops. Gaseous DC breakdown at ~1 Torr develops a similar front, but space-charge coupling between charged species and the dielectric surface leads to an oscillatory anodic current. Increased pressures will lead to further spacecharge effects via increased ionization, and varying the gas species will add additional non-linearity via effects such as oxygen recombination. A distributed seed current influenced by the local triple-point potential could also lead to further space-charge coupling; impact characteristics are significantly altered from the constant-amplitude case, leading to distributed surface charging at the onset of the discharge that will significantly alter the evolution of breakdown. Discharge behaviors using argon and air from vacuum through atmospheric pressures will be discussed, along with characteristic sys- em response to current-source type. Breakdown voltage with respect to various parameters will be presented and compared.