抄録
Evacuated multilayer insulation (MLI) for thermal insulation of the laser interferometer mirror, which is cooled to cryogenic temperatures, is used in the large-scale cryogenic gravitational wave telescope KAGRA. This MLI consists of alternating layers of aluminized polyethylene terephthalate (PET) and lightweight fibrous PET spacers. In a vacuum, however, water molecules outgassed from MLI might degrade the interferometer performance owing to their condensation on the mirror. We have developed new MLIs with thinner PET spacers, whose mass is 30% lighter than that of the conventional one, to reduce outgassing rate. In this study, outgassing rate of new MLIs was measured from the pressure decrease rate in a vacuum chamber for 300 hours. After 100 hours of vacuum testing, its outgassing rate was about half of that for the previous MLI, and comparable to that of electropoloshed stainless steel (SUS304).
