Performance of the helium dewar and the cryocoolers of the Hitomi soft x-ray spectrometer

Abstract

Abstract. The soft x-ray spectrometer (SXS) was a cryogenic high-resolution x-ray spectrometer onboard the Hitomi (ASTRO-H) satellite that achieved energy resolution of 5 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator (ADR). The cooling chain from room temperature to the ADR heat sink was composed of two-stage Stirling cryocoolers, a 4 He Joule-Thomson cryocooler, and superfluid liquid helium and was installed in a dewar. It was designed to achieve a helium lifetime of more than 3 years with a minimum of 30 L. The satellite was launched on February 17, 2016, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the helium tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and the cryocoolers. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Cryocooling technologies for the origins space telescope

“…State-of-the-art mechanical cryocoolers at Technology Readiness Level (TRL) 7+ include Planck, 2 JWST/MIRI, 3 and Hitomi (ASTRO-H). 4 It is worth noting that while the quoted performance of the Joule/Thomson (JT) cryocooler on Hitomi was 4.5 K, the actual cooler temperature under full load was 4.3 K to 4.4 K, so a considerable margin exists on achieving the telescope temperature of 4.5 K. Domestic coolers that could achieve 4.5 K are considered to be TRL 4-5, having been demonstrated as a system in a laboratory environment under NASA's Advanced Cryocooler Technology Development Program (ACTDP) 5 (Fig. 3) or are a variant of a high TRL cooler (JWST/MIRI).…”

“…3) or are a variant of a high TRL cooler (JWST/MIRI). The JWST/MIRI cryocooler engineering unit was tested with a simple substitution of the rare isotope 3 He for the typical 4 He, which produced significant cooling at temperatures below 4.5 K. 6 Mechanical cryocoolers for higher temperatures have already demonstrated impressive on-orbit reliability, 7 with updated space flight operating experience as shown in Fig. 4.…”

“…The TRL 7 JWST/MIRI cryocooler is designed to cool a primary load at 6.2 K and an intercept load at 18 K. It does this using a precooled helium Joule Thomson loop that compresses 4 He from 4 to 12 bar, precools it to 18 K with a three-stage pulse tube cryocooler, then circulates it to a remote heat intercept at 18 K and an isenthalpic expander that provides cooling at 6.2 K. The only change required to lower the temperature to 4.5 K is to lower the return pressure from 4 to 1 bar. To maintain the required mass flow, the compressor swept volume must be increased to accommodate the lower density of the lower pressure helium, and the pressure ratio must be increased to maintain the pressure drop.…”

High-resolution X-ray spectroscopy of astrophysical plasmas with X-ray microcalorimeters

“…Figure 13 shows the schematics of the SXS Dewar and its cooling chain. The sensor chip is cooled down to 50 mK with a three-stage adiabatic demagnetization refrigerator (ADR), 30 l of superfluid liquid helium (LHe), one Joule-Thomson (JT) cooler, and four two-stage Stirling (ST) coolers Fujimoto et al (2017). The nominal lifetime requirement was three years, while the minimum and extra Fig.…”

Lynx x-ray microcalorimeter cryogenic system

“…1 At the same time, it follows a natural progression of instruments based on microcalorimetry starting with XRS/ASTRO-E, XRS2/Suzaku, SXS/ Hitomi, and the X-IFU/Athena using more and more advanced detectors and detector readouts. This progression has also taken advantage of the advancing state of the art in space cryogenics with cooling from 1 to 5 K produced first by stored cryogens (neon and helium on ASTRO-E) 2 to hybrid cryocoolers and stored cryogens (100-K mechanical cooler, solid neon, and liquid helium on Suzaku; 3 4.5-K cryocooler and liquid helium on Hitomi, 4 and Resolve/XRISM) to cryogen-free operation on Athena. 5 One cooler that all of these missions have in common is an adiabatic demagnetization refrigerator (ADR) to cool the detectors to <100 mK.…”