Surface Flashover ARC Orientation on Mylar Film

A study of the arc discharge patterns and resultant damage patterns on thin Mylar films exposed to a 20 keV electron beam is described. In particular, it is established that there is a broad directional correlation among the directions associated with visible linear arcs, damage tracks, the "slow" optical direction and the longitudinal marks left on the film surface as a result of chemical etching. Transverse etch marks also appear to be associated with secondary groups of damage track directions. The "fast" optical direction is associated with the absence of visible arcs or arc damage.