Cryogenic suspension design for a kilometer-scale gravitational-wave detector

Takafumi Ushiba, Tomotada Akutsu, Sakae Araki, Rishabh Bajpai, Dan Chen, Kieran Craig, Yutaro Enomoto, Ayako Hagiwara, Sadakazu Haino, Yuki Inoue, Kiwamu Izumi, Nobuhiro Kimura, Rahul Kumar, Yuta Michimura, Shinji Miyoki, Iwao Murakami, Yoshikazu Namai, Masayuki Nakano, Masatake Ohashi, Koki OkutomiTakaharu Shishido, Ayaka Shoda, Kentaro Somiya, Toshikazu Suzuki, Suguru Takada, Masahiro Takahashi, Ryutaro Takahashi, Shinichi Terashima, Takayuki Tomaru, Flavio Travasso, Ayako Ueda, Helios Vocca, Tomohiro Yamada, Kazuhiro Yamamoto, Simon Zeidler

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


We report the mirror suspension design for large-scale cryogenic gravitational wave telescope, KAGRA, during bKAGRA phase 1. Mirror thermal noise is one of the fundamental noises for room-temperature gravitational-wave detectors such as Advanced LIGO and Advanced Virgo. Thus, reduction of thermal noise is required for further improvement of their sensitivity. One effective approach for reducing thermal noise is to cool the mirrors. There are many technical challenges that must be overcome to cool the mirrors, such as cryocooler induced vibrations, thermal drift in suspensions, and reduction in duty cycling due to the increased number of potential failure mechanisms. Our mirror suspension has a black coating that makes radiative cooling more efficient. For conduction cooling, we developed ultra high purity aluminum heat links, which yield high thermal conductivity while keeping the spring constant sufficiently small. A unique inclination adjustment system, called moving mass, is used for aligning the mirror orientation in pitch. Photo-reflective displacement sensors, which have a large range, are installed for damping control on marionette recoil mass and intermediate recoil mass. Samarium cobalt magnets are used for coil-magnet actuators to prevent significant change of magnetism between room temperature and cryogenic temperature. In this paper, the design of our first cryogenic payload and its performance during bKAGRA phase 1 are discussed.

Original languageEnglish
Article number085013
JournalClassical and Quantum Gravity
Issue number8
StatePublished - 22 Apr 2021


  • Cryogenic suspension
  • Cryogenics
  • Gravitational-wave detector


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