Large-scale cryogenic gravitational wave telescope in Japan called KAGRA is an interferometer equipped with two arms in length of 3 km.
Purpose of KAGRA is direct detection of gravitational waves from the astronomical sources. KAGRA has two notable features to achieve the best sensitivity of detection. The first feature is four test masses cooled down below 20 K in order to reduce thermal noise.
The second feature is that KAGRA was constructed underground of Mt. Ikenoyama to isolate seismic activities from the ground level.
Cryogenic system consisting of cryostat and cryocoolers was designed for the purpose of KAGRA. The cryostat consists of double thermal radiation shields, vacuum chamber and four cryocoolers units as cooling devices for the test mass and the shields. The cryocooler unit to reduce the mechanical noise from the cryocooler smaller than sub-μm order was also developed for the cryogenic system at the same time.
In addition, ultra-high vacuum system without thermally baking was produced and constructed, based on the knowledge of vacuum system for particle accelerators in KEK.
Installation works of the cryogenic system and beam ducts with vacuum pumps of the arms were started October 2014, and the installation works completed on the end of February 2019.
After some of commissioning work including cryogenic performance check, cooling test of the test mass was started, to cool down to 20K. One month after, three test masses had reached around 20 K, and kept the required design temperature. KAGRA with cryo-mirrors is now undergoing commissioning work to join joint observation through global network of gravitational wave telescopes.
The system design of the KAGRA cryogenic and vacuum and its performance at the underground site will be presented in this seminar.
Institute for Cosmic Ray Research, University of Tokyo
Cryogenic and Vacuum Technologies of the Interferometric Cryogenic Gravitational Wave Telescope, KAGRA
On behalf of KAGRA Collaboration