1. Status of the cryogenic payload system for baseline KAGRA Rahul Kumar 1, K. Craig 2, K. Yamamoto 2, H. Tanaka 2, T. Miyamoto 2,T. Kajita 2, T. Suzuki 1, T. Tomaru 1 and the Cryopayload Group 1 High Energy Accelerator Research Organization (KEK) 2 Institute for Cosmic Ray Research (ICRR), University of Tokyo Presented at the KAGRA face to face meeting, ICRR, The University of Tokyo, Kashiwa, 21-23 Feb 2016

2. Outline Cryogenic payload Prototype sapphire test suspensions On-going experiments Suspensions rod: strength test/thermal conductivity Platform stage re-design Interferometer Beamsplitter thermal noise Conclusions 2

3. Cryogenic Payload system IM recoil mass and heat link are not shown Sapphire Mirror Recoil Mass Bottom IM Sapphire fibers CuBe blades Moving mass Platform stage Marionette Moving Mass for the Marionette Sapphire mirror 23 kg Earth quake stoppers Intermediate mass (23 kg)

4. Sapphire fibres 23 kg Sapphire test mass mirror Sapphire blade springs Length 350 mm Sapphire ear Sapphire Nail heads 4 Indium bonds at blade springs Indium bonds at ears Hydroxide Catalysis Bonding Bond thickness – 100 nm Typical strength – 25 MPa to 50 Mpa Q value – 3000 (at 20 k) Indium bonds Melts at 160 0 C Bond thickness – 10 microns Q value – 320 (20 kelvin)

5. 3.33×10 -19 Strain at 10 Hz /√Hz Baseline requirement 6.63×10 -22 FEA (Estimated)2.23×10 -22 Suspension thermal noise: Estimated using FEA modeling techniques developed for the advanced LIGO detector 5 baseline

6. Prototype Sapphire Test Suspensions Sapphire mass (22 kg) with side cuts for ear attachment Sapphire ear Sapphire blades Sapphire fibres 350 mm Sapphire nail head 10 mm 1 st prototype sapphire test suspensions to be fabricated in 2016 6

7. Preparation of jigs ongoing CAD model by Kieran Craig (ICRR) 7 22 kg 23 kg Quarter size (KAGRA) cryostat at KEK

8. Materials Titanium Alloy or Maraging steel  Strength test and thermal conductivity measurement under cryogenic conditions at KEK Rod suspending the cryogenic payload system 8 Cryogenic suspensions rod Load 200 kg Load 70 kg Room temp. type A system developed by NAOJ Cryogenic stage KEK & ICRR

9. 296 Hz 412 Hz 0.6 m Thickness 0.027 m Mass 47 kg 9 Platform stage re-design

10. Levin’s approach for thermal noise calculation Aluminium post Epoxy EP30 100 microns Off-resonance thermal noise at 100 Hz 9.31128× 10 -19 10 Beamsplitter thermal noise

11. Displacement noise requirements of auxiliary mirrors 11 Beamsplitter TN

12. Conclusions Development of cryogenic payload system is still ongoing Estimated (FEA) TN to be within the bKAGRA requirements First prototype sapphire test suspensions to be fabricated in 2016 Sapphire test suspensions will be cooled to 20 kelvin Thermal conductivity and Q of the system to be measured Development and testing of components for the cryogenic payload is still ongoing Beamsplitter thermal noise within KAGRA baseline requirements 12