Porous plug phase separator and superfluid film flow suppression system for the soft x-ray spectrometer onboard Hitomi

Yuichiro Ezoe, Michael DiPirro, Ryuichi Fujimoto, Kumi Ishikawa, Yoshitaka Ishisaki, Kenichi Kanao, Mark Kimball, Kazuhisa Mitsuda, Ikuyuki Mitsuishi, Masahide Murakami, Hirofumi Noda, Takaya Ohashi, Atsushi Okamoto, Yohichi Satoh, Kosuke Sato, Peter Shirron, Shoji Tsunematsu, Hiroya Yamaguchi, Seiji Yoshida

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


When using superfluid helium in low-gravity environments, porous plug phase separators are commonly used to vent boil-off gas while confining the bulk liquid to the tank. Invariably, there is a flow of superfluid film from the perimeter of the porous plug down the vent line. For the soft x-ray spectrometer onboard ASTRO-H (Hitomi), its approximately 30-liter helium supply has a lifetime requirement of more than 3 years. A nominal vent rate is estimated as ∼30 μg/s, equivalent to ∼0.7 mW heat load. It is, therefore, critical to suppress any film flow whose evaporation would not provide direct cooling of the remaining liquid helium. That is, the porous plug vent system must be designed to both minimize film flow and to ensure maximum extraction of latent heat from the film. The design goal for Hitomi is to reduce the film flow losses to <2 μg/s, corresponding to a loss of cooling capacity of <40 μW. The design adopts the same general design as implemented for Astro-E and E2, using a vent system composed of a porous plug, combined with an orifice, a heat exchanger, and knife-edge devices. Design, on-ground testing results, and in-orbit performance are described.

Original languageEnglish
Article number011203
JournalJournal of Astronomical Telescopes, Instruments, and Systems
Issue number1
Publication statusPublished - 2018 Jan 1


  • ASTRO-H (Hitomi)
  • cryogenics
  • film flow
  • porous plug
  • soft x-ray spectrometer
  • superfluid helium
  • x-ray microcalorimeter

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Control and Systems Engineering
  • Instrumentation
  • Astronomy and Astrophysics
  • Mechanical Engineering
  • Space and Planetary Science


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