On-orbit performance of the Resolve Adiabatic Demagnetization Refrigerator on XRISM

The Resolve instrument on XRISM performs high-resolution spectroscopy in the soft x-ray band using a 6x6 microcalorimeter array cooled to 50 millikelvin by a 3-stage ADR. The use of 3 stages enables the ADR to use a tank of superfluid helium at 1.2 K or a Joule-Thomson (JT) cryocooler operating at <4.5 K as its heat sink. Resolve launched in September of 2023 with approximately 35 liters of helium, which has a projected lifetime of >4 years. When the liquid is depleted, the ADR enters a cryogen-free mode of operation, which can be sustained as long as the JT and other cryocoolers remain fully operational. Details of the ADR’s design and performance will be presented.