Pulsed volume and surface discharges in an SF₆ environment

Volume and surface discharges in SF₆ are investigated to support refurbishment of the Z-machine's Laser Triggered Gas Switch, LTGS, at Sandia National Laboratories (SNL). The recently upgraded LTGS has exhibited a failure mode which results in surface flashover on the inside of the dielectric switch envelope. These flashover events degrade the LTGS performance and cause a pre-fire in the successive shot. In the following, experimental results of both volume breakdown and surface flashover across different dielectric materials in SF₆ primarily at 20 psig are presented. In addition to fast voltage and current monitoring of the breakdown events, there was an emphasis put on imaging and optical emission spectra (̃200 nm to ̃700 nm). As much as possible, the laboratory experiment was designed to reproduce the conditions found in the 5.5 MV LTGS. The principal physical mechanisms involved in surface flashover at various pressures of SF₆ are vital to the understanding of this specific switch failure mode.