Puncture discharges in surface dielectrics as contaminant sources in spacecraft environments

The spacecraft charging phenomenon was simulated in a laboratory vacuum chamber by irradiating suitable dielectric targets with an electron beam operating at accelerating potentials from 0-34 kV. In addition to static measurements and photographic examination of the puncture discharges in Teflon samples, the transient characteristics of the electrical discharges were determined from oscillographs of voltage and current and by charged particle measurements employing a biased Faraday cup and a retarding potential analyzer. Using these latter techniques, studies of angular and energy distributions of charged particles indicate an initial burst of high energy electrons (5 x 10 to the 13th power per discharge at energies greater than 3000 eV) followed by a less intense burst of lower energy negative particles. Positive ions are emitted from the discharge site in an initial high velocity burst followed by a lower velocity burst tentatively identified as carbon.