Detector Assembly and the Ultralow-Temperature Refrigerator for XRS

The x-ray spectrometer (XRS) on the Japanese Astro-E observatory is the first ultra low temperature space borne instrument. The system utilizes a 900g ferric ammonium alum adiabatic demagnetization refrigerator (ADR) with 3 He gas gap heat switch to cool the detector assembly to 0.060 K. The system operates in a 'single shot' configuration allowing the system to remain at its operating temperature for about 40 hours in the lab before executing a recharge cycle. The on-orbit performance is expected to be about 36 hours with a 97 percent duty cycle. The detector assembly for XRS consists of a 32 channel microcalorimeter array, bias electronics, thermometry, and an anti-coincidence detector that are attached to the cold stage of the ADR. To thermally isolate the detector system from the superfluid helium reservoir, the detector system is suspended by Kevlar cords and electrical connection is made by 130, 20 micron diameter, tensioned NbTi leads. The detectors are read out in a source-follower arrangement using FET amplifiers operating at 130 K mounted in nested, thermally-isolated assemblies that also use Kevlar suspension and stainless steel wiring. The design and thermal performance of this system will be discussed.