Design and performance of the Hitomi/XRISM adiabatic demagnetization refrigerator controller

The Resolve instrument in the recently launched X-ray Imaging and Spectroscopy Mission (XRISM) is a rebuild of the Soft X-ray Spectrometer (SXS) in Hitomi (aka Astro-H which had an unfortunately brief mission life in 2016). Resolve is a high-resolution non-dispersive soft x-ray spectrometer from nominally 0.3 keV to 12 keV based on a calorimeter detector array operating at 50 mK with a resolution better than 7 eV FWHM at 6 keV. For such sensitive cryogenic instruments, temperature stability has a strong impact on the detector’s performance.

The Adiabatic Demagnetization Refrigerator Controller (ADRC) in the XRISM Resolve instrument is the electronics box (ebox) responsible for the high-precision sub-K temperature readout and control of the multi-stage Adiabatic Demagnetization Refrigerator (ADR) subsystem. To achieve the science objectives stated above, the ADRC must provide a thermal stability better than 2.5 μK RMS (over a 10-minute interval) for the calorimeter detectors in both cryogen (liquid helium) and cryo-free modes. The ADRC has direct telemetry/command and power interfaces with the spacecraft and also provides sensor read-out and heater circuits for decontamination of the filters in the cold aperture.

As a part of the discussion on the design and performance of the ADRC, this paper will also include an overall view of the 50 mK temperature control, plus monitor and control of the aperture filter temperature for de-contamination purpose.