Expansion of a Surface Flashover Plasma

A strong electric field applied parallel to the surface of a dielectric in vacuum can lead to the formation of a vacuum surface flashover discharge, which will produce light, neutral gas, and plasma. Plasma formed in this way can be used for a number of applications, including as a source of electrons, but the plasma's expansion away from the discharge site will impact its usefulness for those applications. Here, we report measurements on the expansion of a surface flashover plasma generated from a pulsed discharge in vacuum, using electric fields on the order of 10 MV/m applied across a Plexiglas sample. Expansion velocity and energy distribution measurements were made using a moveable, biased detector probe. The temporal structure of the plasma arriving at the probe was found to have a characteristic shape, indicating the presence of three different components of the plasma having different velocities in the range of 1–9
${\rm cm}/\mu{\rm s}$
. The pulser charging voltage was found to have a noticeable effect on the plasma energy distributions, but only a small effect on the plasma expansion velocity.