Ultrahigh Vacuum Cryostat System for Extended Low-Temperature Space Environment Testing

摘要

The range of temperature measurements have been significantly extended for an existing space environment simulation test chamber used in the study of electron emission, sample charging and discharge, electrostatic discharge and arcing, electron transport, and luminescence of spacecraft materials. This was accomplished by incorporating a new two-stage, closed-cycle helium cryostat which has an extended sample temperature range from ${<}{40}$ to ${>}{rm 450}~{rm K}$, with long-term controlled stability of ${<}{rm 0.5}~{rm K}$. The system was designed to maintain compatibility with an existing ultrahigh vacuum chamber (base pressure ${<}10^{-7}~{rm Pa}$) that can simulate diverse space environments. These existing capabilities include controllable vacuum and ambient neutral gases conditions $({<}10^{-8}hbox{-}10^{-1}~{rm Pa})$, electron fluxes (5–30-keV monoenergetic, focused, and pulsed sources over $10^{-4}hbox{-}10^{10}~{rm nA}hbox{-}{rm cm}^{-2}$), ion fluxes ( ${<}{0.1}hbox{-}5~{rm keV}$ monoenergetic sources for inert and reactive gases with pulsing capabilities), and photon irradiation (numerous continuous and pulsed monochromated and broad band IR/VIS/UV $[0.5hbox{-}7~{rm eV}]$ sources). The new sample mount accommodates one to four samples of 1–2.5-cm diameter in a low-temperature carousel, which allows rapid sample exchange and controlled exposure of the individual samples. Custom - emispherical grid retarding field analyzer and Faraday cup detectors, custom high speed, high-sensitivity electronics, and charge neutralization capabilities used with ${<}{rm 50}~{rm pA}$, ${<}{rm 5}~mu{rm s}$, and ${<}3times 10^{3}$ electrons/pulse pulsed-beam sources permit high-accuracy electron emission measurements of extreme insulators with minimal charging effects. In situ monitoring of surface voltage, arcing, and luminescence (250–5000 nm) have recently been added.