KAGRA detector is a 2nd generation, large-scale cryogenic gravitational wave telescope
(LCGT), currently being built in Japan for the detection of gravitational waves. The arm-length of
this interferometric gravitational wave detector is 3 km and is located 200 m underground in the
Kamioka mine (near Toyama, Japan). KAGRA is a cryogenic temperature detector (mirrors and
suspension called cryogenic payload will be cooled to 20 K) which is unique when compared to
other room temperature detectors around the world. Operating the detector at cryogenic
temperature will reduce the thermal noise in the suspension (mirrors) and allow the instrument
to achieve very high sensitivity which is essential to define the emerging field of gravitational
wave astronomy. The cryogenic payload for KAGRA is in the form of multiple pendulum, housed
in a cryostat (with four cryo-cooler units) operating at 20 Kelvin. The use of sapphire (Al2O3) as
a substrate material for the suspension system is the baseline design for the KAGRA detector.
Sapphire is a crystalline material and is an ideal candidate at low temperature since it exhibits
extremely low mechanical loss and shows several benefits including good optical properties and
high thermal conductivity.
In this talk I will discuss about the current status of the KAGRA detector, including the ongoing R&D and installation activities at the detector site. The design and status of the cryogenic payload system, specifically focussing on the performance of the sapphire suspensions will be presented. There are several noise sources which affects the performance of a detector at frequencies below 100 Hz. I will discuss such noise sources and the methods to reduce them. My talk will also include the development of ultra-sensitive low noise mirror suspensions system for the advanced LIGO detector.