THERMAL DESIGN OF THE XRS HELIUM CRYOSTAT

The required lifetime for the Astro-E X-Ray Spectrometer (XRS) is 2 ye ars, with a goal of 2.5 years. To meet this requirement, significant a dvances in state-of-the-art long-life cryogenic systems are required. The XRS system is a hybrid neon/helium system with a final stage of co oling provided by an adiabatic demagnetization refrigerator. The therm al design of the helium cryostat is described in this paper. To achiev e a lifetime of 2.5 years with a helium volume of approximately 20 lit res, the heat load on the helium must be of the order of 800 mu W or l ess. The expected lifetime and sensitivity of the lifetime to changes in the design or external heat loads is modelled. Results of prelimina ry thermal conductivity measurements are presented and future tests ar e identified. A study of heat loads that were small enough to be negle cted in previous designs of long-life cryogenic systems was undertaken . A summary of the findings is presented. (C) 1996 Elsevier Science Li mited