SGEMP Response Investigations with Exploding-Wire Photons

The exploding-wire photon experiments produced space-charge-limited boundary layers of thickness as small as a few centimeters. Comparison between the experimental results and state-of-the-art SGEMP calculations revealed the following features. Peak electric fields, surface currents and currents coupled into simple geometries were calculated within a factor of 1.5, with no normalization other than photoemission diode measurements of the electron current and average energy. Absolute agreement at low fluxes indicate that the electron-emission coefficients are measured by the diodes to an accuracy of better than 30%. The larger scatter in data at high fluxes on the disk experiment may be due to a combination of photon spectrum and rise time variations (especially in a soft component) between pulses and could possibly be affected by differences in minor contaminants on the test object and diode surfaces. The ratio of currents on the back and front of the disk is calculated to be a factor of 1.5 greater than measured. This discrepancy cannot depend on electron emission, and may indicate a need for finer gridding in calculating the edge of a disk. The leakage of electrons into a shadowed aperture is calculated within a factor of 1.4, but appears to persist somewhat longer than the calculations indicate.