Detector configuration of KAGRA-the Japanese cryogenic gravitational-wave detector

The construction of the Japanese second-generation gravitational-wave detector KAGRA (previously called LCGT) has been started. In the next 6-7 years, we will be able to observe the spacetime ripple from faraway galaxies. KAGRA is equipped with the latest advanced technologies. The entire 3 km long detector is located in the underground to be isolated from the seismic motion, the core optics are cooled down to 20 K to reduce thermal fluctuations and quantum non-demolition techniques are used to decrease quantum noise. In this paper, we introduce the detector configuration of KAGRA, its design, strategy and downselection of parameters.