Anode-Initiated Vacuum Insulator Flashover Experiments and Modeling*

Vacuum insulator flashover is a breakdown process occurring along a dielectric surface separating electrode surfaces. Here, the dielectric is a separation barrier between vacuum and water-containing (or oil-containing) sections in pulsed power systems. While one kind of breakdown process, cathode-initiated flashover, is somewhat understood (an electron cascade resulting in surface charge saturation), other processes are hypothesized for anode-initiated breakdowns. One hypothesized process involves plasma initiation due to high fields at the anode triple junction and subsequent advancement and growth of a breakdown “spot” along the insulator towards the cathode. This process has some phenomenological overlap with positive streamers. This work will describe recent efforts to better understand anode-initiated flashover, including experimental investigation of the location and timing of various species emissions and plasma growth. A high-fidelity PIC-DSMC modeling approach using Sandia’s massively parallel plasma simulation code, Aleph, will be described, including multiple neutral, excited state, and ion species. Challenges with various emission models will be explored.