111 Kazuhiro Yamamoto Institute for Cosmic Ray Research, the University of Tokyo Cryogenic interferometer technologies 19 May 2014 Gravitational Wave Advanced Detector Alyeska Resort, Girdwood, Alaska, U.S.A. 2 0. Abstract Cryogenic technologies (1)How much target of mirror temperature in interferometer operation ? What we must take care of ? (2)Initial cooling time is an issue. How can we reduce ? (3)What are large open issues for cryogenic suspension ? 3 Contents 1.Introduction 2.Operative temperature 3.Initial cooling time 4.Status of the art and needed developments 5.Summary 44444 Motivation : Why the mirrors and suspension are cooled ? (1)Small thermal noise (2)Small thermal lens (3)Less serious parametric instability (4)Small cosmic ray effect 1.Introduction T. Tomaru et al., Classical and Quantum Gravity 19 (2002) K. Yamamoto et al., Journal of Physics: Conference Series 122 (2008) K. Yamamoto et al., Physical Review D 78 (2008) Kenji Numata and Kazuhiro Yamamoto, Chapter 8. Cryogenics, in Optical Coatings and Thermal Noise in Precision Measurement Cambridge University Press (2012). 55555 Room temperature second generation interferometer Fused silica mirror suspended by fused silica fibers 1.Introduction 66666 Room temperature second generation interferometer Fused silica mirror suspended by fused silica fibers 1.Introduction This suspension is not a good for cryogenics. Large mechanical dissipation and low thermal conductivity at low temperature Other material with small dissipation and high thermal conductivity Sapphire or Silicon Operative temperature 7 In principle, lower temperature is better. Sapphire > 50K Constant