Dielectric Surface Discharges: Effectsof Combined Low-Energy and High-Energy Incident Electrons

In simulation of the exposure of spacecraft insulating materials to the energetic-electron environment of synchronous orbit, a study has been made of the effect on dielectric surface discharges of adding high energy electrons at 5 pA/cm2 to a primary 20 keV, 10 nA/cm2 electron beam, the high-energy broad spectrum particles having been produced by the ß-decay of Strontium-90. Kapton exhibits the most surprising effects, which are significantly increased discharge strength, increased waiting time between discharges, and a decreased number of discharges per specimen before discharge cessation. Mylar exhibits similar but less pronounced effects, while Teflon is relatively unaffected. There is evidence that with Kapton and Mylar the high energy electrons act in some way to delay the instant of discharge ignition so that more charge can be accumulated during chargeup and hence released during arc discharge.