Pin-to-Plane Breakdown Through a Thin-Film Dielectric Coated Electrode: PIC-DSMC Simulations compared to Experimental Results

In devices where high voltages are present, dielectric coatings are often used to increase the standoff voltage in the presence of an air-filled gap. These coatings are typically thin (<1mm) compared to the gap size (~cm) and, if the entire device surface can be coated, then breakdown will occur when the air-gap streamer produces fields in the dielectric film that exceed its breakdown strength. This results in breakdown through the air and dielectric film. Here we will show experimentally measured breakdown voltage for several combinations of dielectric coating thicknesses and gap sizes and compare them to 2D electrostatic PIC-DSMC simulations using the Sandia code EMPIRE. Thus far, both the simulations and a series of experimental shots have shown that in a 1mm gap with a 500µm thick dielectric coating the arc always travels along the dielectric surface until it reaches the sample edge (>2cm radius) where there is uncoated metal held at ground. For a 1mm gap with a 100µm thick dielectric coating the simulations show that breakdown should occur through the dielectric film and the experiments show that sometimes the breakdown occurs through the film and sometimes the arc still travels along the dielectric to the sample edge (5cm).