J.R. Dennison

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Dielectric materials subjected to energetic electron fluxes can emit light in several forms. We have observed three distinct types of emissions: (i) short-duration (<1 ms), high-intensity electrostatic discharge (ESD) or “arc” events; (ii) intermediate-duration, high-intensity events which begin with a bright arc followed by an exponential decay of intensity (~10 to 100 s decay constant), termed “flares”; and (iii) long-duration, low-intensity emission, or cathodoluminescence, that continues as long as the electron flux is on. These events were studied for bulk samples of bisphenol/amine epoxy, using an electron gun with varying current densities (0.3 to 5 nA/cm2) and energies (12 to 40 keV) in a high vacuum chamber. Light emitted from the samples was measured with a high-sensitivity visible to near-infrared video camera. Results of the spatial and temporal extent for each type of event are presented as well as a discussion of how absolute spectral radiance and rates for each type of event are dependent on incident electron current density, energy, and power density and on material type, temperature, and thickness. Applications of this research to spacecraft charging and light emissions are discussed.

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