Surface discharges on Teflon, Mylar and Kapton

FEP Teflon, Mylar and Kapton H are compared from the point of view of charged-area scaling of discharge current pulse properties. The properties measured are peak current, pulse duration, released charge and energy dissipated in a load resistor, all for 20 keV incident electrons at a current density of 80 nA/sq cm. In general, it is found that the three materials are more similar than dissimilar, and furthermore, that this similarity extends to discharge damage as well, the damage being identified as a combination of subsurface filamentary tunnels and surface grooves. The experimental observations are used to motivate a theory of discharge arc propagation in which the propagation velocity is controlled by the rate of removal of excess charge via wave propagation along a filamentary tunnel filled with an overdense plasma.