Review of experimental research on Joule–Thomson cryogenic refrigeration system

Development of mechanical cryocoolers for the cooling system of the Soft X-ray Spectrometer onboard Astro-H

Development of the active magnetic regenerative refrigerator operating between 77 K and 20 K with the conduction cooled high temperature superconducting magnet

Magnetic refrigerants with a large magnetocaloric effect (MCE) in a wide temperature range and low magnetic ordering temperature (To) in the sub-kelvin temperature region are not only crucial for adiabatic demagnetization refrigeration but also open up a broader parameter space for the optimal design of adiabatic demagnetization refrigerators. However, such magnetic refrigerants are extremely rare because they require magnetic materials to simultaneously satisfy three conditions: low To, weak magnetic interaction, and high magnetic density. Here, we report the syntheses, heat capacities, and magnetic properties of Gd(OH)3-xFx (1: x = 1, 2: x ≈ 1.5, and 3: x = 2), demonstrating for the first time that the introduction of fluoride anions into antiferromagnetic Gd(OH)3 can effectively regulate its To. Significantly, 3 not only has a To of 0.5 K but also exhibits a large MCE in the temperature range from 0.5 to 4 K, representing the best magnetic refrigerant reported to date in the temperature range of 0.5-4 K from the viewpoint of the MCE.

Gd(OH)F2: A Promising Cryogenic Magnetic Refrigerant.

The Soft X-ray Spectrometer (SXS) instrument that flew on the Astro-H observatory was designed to perform imaging and spectroscopy of x-rays in the energy range of 0.2 to 13 keV with a resolution requirement of 7 eV or better. This was accomplished using a 6x6 array of x-ray microcalorimeters cooled to an operating temperature of 50 mK by an adiabatic demagnetization refrigerator (ADR). The ADR consisted of three stages in order to operate using either a 1.2 K superfluid helium bath or a 4.5 K Joule-Thomson (JT) cryocooler as its heat sink. The design was based on the following operating strategy. After launch, while liquid helium was present (cryogen mode), two of the ADR's stages would be used to single-shot cool the detectors, using the helium as a heat sink. When the helium was eventually depleted (cryogen-free mode), all three ADR stages would be used to continuously cool the helium tank to about 1.5 K, and to single-shot cool the detectors (to 50 mK), using the JT cryocooler as a heat sink. The Astro-H observatory, renamed Hitomi after its successful launch in February 2016, carried approximately 36 liters of helium into orbit. Based on measurements during ground testing, the average heat load on the helium was projected to be 0.66 mW, giving a lifetime of more than 4 years. On day 5, the helium had cooled to <1.4 K and ADR operation began, successfully cooling the detector array to 50 mK. The ADR's hold time steadily increased to 48 hours as the helium cooled to a temperature of 1.12 K. As the commissioning phase progressed, the ADR was recycled (requiring approximately 45 minutes) periodically, either in preparation for science observations or whenever the 50 mK stage approached the end of its hold time. In total, 18 cycles were completed by the time an attitude control anomaly led to an unrecoverable failure of the satellite on day 38. This paper presents the design, operation and on-orbit performance of the ADR in cryogen mode as the foreshortened mission did not provide an opportunity to test cryogen-free mode.

/pdf/design-and-on-orbit-operation-of-the-soft-x-ray-spectrometer-3rg4a948k1.pdf

Design and on-orbit operation of the soft x-ray spectrometer adiabatic demagnetization refrigerator on the Hitomi observatory

Design and predicted performance of the 3-stage ADR for the Soft-X-ray Spectrometer instrument on Astro-H

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Design and predicted performance of the 3-stage ADR for the Soft-X-ray Spectrometer instrument on Astro-H