Cryogen free cooling of ASTRO H SXS Helium Dewar from 300 K to 4 K
Abstract Soft X ray Spectrometer instrument (SXS) is one of the primary scientific instruments of ASTRO H. SXS has a cold detector that is cooled to 50 mK by using a multi stage Adiabatic Demagnetization Refrigerator (ADR) SXS Dewar containing ADR provides 1.3 K heat sink by using liquid helium in nominal operation. After liquid helium is dried up, 4 K heat sink is provided by using mechanical coolers. Both nominal operation and cryogen free operation were successfully demonstrated. This paper describes the test result of cryogen free operation and cool down performance from room temperature by using only mechanical coolers without liquid helium. The coolers on the Dewar cooled down cold mass from around 300 K to 4 K with 260 W electric power in 40 days. Cold mass is 35 kg in 4 K area including the helium tank, ADR and detector assembly.