KAGRA (formerly the Large-scale Cryogenic Gravitational wave Telescope, LCGT) will be a highly sensitive detector for gravitational waves and part of a world-wide network with LIGO, VIRGO and others. This Japanese project is hosted by the Institute for Cosmic Ray Research of the University of Tokyo, with NAOJ and KEK serving as co-hosts and with participation by various universities/institutes throughout the world.
Features of the Telescope
This telescope is quite different from optical telescopes and radio telescopes. It is a laser interferometer which detects faint space-time distortion as described in "Detection of Gravitational Waves". In order to increase the sensitivity of the interferometer, advanced technologies such as a high-power laser source, large-aperture ultra-low-loss mirrors, and a ultra-high-vacuum vacuum system will be used.
The main features of the telescope are listed below.
- 1The size of telescope is 3 kmWe designed the KAGRA detector to have an arm length of 3km to both compete and cooperate with other detectors around the world. Italy and France have a joint project Virgo with 3-km arms. In the United States, aLIGO has two 4-km detectors (with parts for a third that is planned to be constructed in India).
- 2The telescope is to be constructed in an underground mineGW detection is a precise distance measurement, and seismic motion is a limiting noise source of the detector. We have selected the Kamioka mine at Hida, in the Gifu prefecture of Japan as a seismically quiet site.
- 3The mirrors are cooled down to cryogenic temperature of -250 Celsius degree (20 Kelvin)The mirrors are cooled so as to reduce thermal vibration of the mirror material.
- 4Sapphire is used as the material of the mirror.Sapphire is one of the best materials for a cryogenic GW interferometer because it has excellent both optical and thermal properties at cryogenic temperatures.
Features 2-4 above are unique to KAGRA.
CLIO: Prototype Cryogenic Detector
Since KAGRA will be the first large interferometer gravitational wave detector with cryogenic mirrors, it was necessary to demonstrate the feasibility of cryogenic operation. The gravity wave group of the Institute for Cosmic Ray Research built a 100-m length prototype interferometer, CLIO, in the Kamioka mine. The Gravitation Wave Project Office of NAOJ has been cooperating with ICRR group for the development of CLIO.
CLIO successfully demonstrated the reduction of the thermal noise by the cooling of the mirrors.