Progress on the cryogenic system for the KAGRA cryogenic interferometric gravitational wave telescope

KAGRA is a project to construct a cryogenic interferometric gravitational wave detector in Japan. Its mirrors and the lower parts of the suspension systems will be cooled to 20 K in order to reduce thermal noise, one of the fundamental noise sources. One of the key features of KAGRA's cooling system is that it will keep the mirrors cooled without introducing vibration. This paper describes the current status of the design, manufacture and testing of the KAGRA cooling system.