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12th Spacecraft Charging Technology Conference 14-18 May, 2012 Kitakyushu Japan

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A versatile vacuum system for long duration testing of materials modifications due to exposure to simulated space environment conditions has been designed and built. The chamber is particularly well suited for cost-effective tests of multiple small scale materials samples over prolonged exposure. Critical environmental components simulated include neutral gas [ultrahigh vacuum (10-7 Pa) to ambient], FUV/UV/VIS/NIR solar spectrum, electron plasma fluxes, and temperature. The UV/VIS/NIR solar spectrum is simulated using an external, normally incidence and collimated class AAA Solar Simulator source, with standard Air Mass Zero (AM0) filters to shape the incident radiation spectrum. This Xe arc discharge tube source has a 200 nm to 2000 nm range with up to four suns light intensity capability. Light intensity feedback is used to maintain the intensity temporal stability during the sample exposure cycle, with standard calibrated solar cells mounted internally on the sample mounting block. Incident FUV (far ultraviolet) intensity radiation is provided by Kr discharge line sources, with a primary emission line at 124 nm and secondary emission line at 117 nm with up to four suns intensity. This provides an adequate substitution for the solar FUV spectrum, which is dominated by the ultraviolet hydrogen Lyman α emission line at 122 nm. An electron flood gun provides a uniform, monoenergetic (~20 eV to ~15 keV) electron flux. Electron fluxes at the sample surface of1 μA-cm-2 are continuously monitored during the sample exposure cycle, using a standard Faraday cup mounted on the sample block. The chamber maintains ≤98% uniformity of the electromagnetic and electron radiation exposure over a sample area of ~70 cm2. Samples are mounted on a rotatable OFHC Cu sample block with large thermal mass to minimize the differences in temperature between samples and thermal fluctuations during the sample exposure cycle. A controlled, uniform temperature range from 100 K to 450 K is achieved using a cryogenic reservoir and resistance heaters attached to the sample block. The sample carousel is attached to a standard rotational vacuum feedthrough, to allow 355° rotation of the samples relative to the incident fluxes. Reflectivity and emissivity are measured by extending a compact integrating sphere with a fiber optic connection to an external calibrated commercial UV/VIS/NIR spectrometer and an IR absorptivity/emissivity probe mounted on a linear translation stage toward the center of the chamber; each sample and in situ calibration standards are rotated under the probes in turn. An automated data acquisition system periodically monitors and records the environmental conditions, UV/VIS/NIR reflectivity, and IR emissivity of the samples in situ during the sample exposure cycle.


Poster presented at 12th Spacecraft Charging Technology Conference 14-18 May, 2012 Kitakyushu Japan

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