KAGRA Cryogenic Suspension Control toward the Observation Run 3

Abstract

Abstract We have newly developed a vibration isolation system to reduce vibration via heat links, which would be one of the obstacles in the control of KAGRA gravitational wave detector. KAGRA adopts cryogenic mirrors for main optics to reduce thermal noise, which is a fundamental noise source in ground-based gravitational wave detectors in 100 Hz region, and achieves the best sensitivity in this frequency region in the world. The cryogenic mirror needs to be cooled down rapidly not to waste observation time and quietly not to disturb the mirror suspension system. For the former, radiative cooling works effectively with black coatings in high temperature region. Conductive cooling will strongly work with heat links in low temperature. However, according to our calculation, it was revealed that vibration via heat links impairs the detector sensitivity in several dozen Hz. The cryogenic suspension with heat links needs to be properly controlled up to almost same frequency region, thus, we have focused on reducing transmitting vibration with Heat Link Vibration Isolation System. In this paper, we will introduce the cryogenic suspension system, cooling system and Heat Link Vibration Isolation System in KAGRA.