Evaluation of heat extraction through sapphire fibers for the GW observatory KAGRA

Abstract

Currently, the Japanese gravitational wave laser interferometer KAGRA is under construction in the Kamioka mine. As one main feature, it will employ sapphire mirrors operated at a temperature of 20K to reduce the impact from thermal noise. To reduce seismic noise, the mirrors will also be suspended from multi-stage pendulums. Thus the heat load deposited in the mirrors by absorption of the circulating laser light as well as heat load from thermal radiation will need to be extracted through the last suspension stage. This stage will consist of four thin sapphire fibers with larger heads necessary to connect the fibers to both the mirror and the upper stage. In this paper, we discuss heat conductivity measurements on different fiber candidates. While all fibers had a diameter of 1.6mm, different surface treatments and approaches to attach the heads were analyzed. Our measurements show that fibers fulfilling the basic KAGRA heat conductivity requirement of $\kappa \ge$5000W/m/K at 20K are technologically feasible.

arXiv comment11 pages, 4 figures

References in corpus (5)

• First Long-Term Application of Squeezed States of Light in a Gravitational-Wave Observatory
• Measurement of the mechanical loss of a cooled reflective coating for gravitational wave detection
• Cryogenic measurement of the optical absorption coefficient in sapphire crystals at 1.064(micro)m for the Large-scale Cryogenic Gravitational wave Telescope
• Ultra-stable performance of an underground-based laser interferometer observatory for gravitational waves
• Status of the GEO 600 squeezed-light laser

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• Cryogenic suspension design for a kilometer-scale gravitational-wave detector
• Mirror actuation design for the interferometer control of the KAGRA gravitational wave telescope
• Particle swarm optimization of the sensitivity of a cryogenic gravitational wave detector
• Molecular adsorbed layer formation on cooled mirrors and its impacts on cryogenic gravitational wave telescopes
• Cryogenic payloads for the Einstein Telescope -- Baseline design with heat extraction, suspension thermal noise modelling and sensitivity analyses
• Thermal noise of a cryo-cooled silicon cantilever locally heated up to its melting point