大型低温重力波望遠鏡用 3 km 大口径真空ダクトの製作

The LCGT (Large-scale Cryogenic Gravitational wave Telescope) is an interferometer of 3-km long baseline, using a laser beam of 1064-nm wavelength. The entire system of the interferometer is to be operated in a vacuum for avoiding any noises caused by in-space molecules and adsorbed molecules on the mirrors. The beam tubes of 3 km long and 800 mm in diameter are to be kept in the order of 10−7 Pa so as to reduce scattering-effects due to residual gas molecules. In April 2011, production of 484 of unit tubes of 12 m long and 800 mm in diameter, having a flexible bellows and flanges, were started. In this report, the production process of the unit tubes is described concerning surface treatment for outgas reduction.