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Present Design of LCGT Cryogenic Payload - Status of Cryogenic Design -

This article provides an overview of the design of the cryogenic payload for the Laser Interferometer Gravitational-Wave Observatory (LCGT), including the structure of the cryostat and the estimation of heat load from the beam duct shields. The article also discusses the cryostat's response to ground motion and the thermal budget of the cryostat.

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Present Design of LCGT Cryogenic Payload - Status of Cryogenic Design -

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  1. Present Design of LCGT Cryogenic Payload- Status of Cryogenic Design - N. KIMURA*, Y. SAKAKIBARA**, S. KOIKE*, T. OHMORI***, T. SUZUKI*, H. YAMAOKA*, and LCGT Collaboration * High Energy Accelerator Research Organization (KEK) ** University of Tokyo *** Teikyo University

  2. Outline • Design of the LCGT cryogenics • Structure of the cryostat • Cryostat response to ground motion • at CLIO/Kamioka mine • Thermal Budget of the cryostat • Estimation of heat load of the Mirror • from the beam duct shields • (by Mr. SAKAKIBARA) • Summary

  3. Location of Four Mirror Cryostats with the Cryo-coolers for the LCGT Mozumi-End Atotsu-End Y-Front Room X-Front Room Connection Port to SAS Mirror a cryostat Gate valve Gate valve L=~20 m L=~20 m Vacuum duct800 with radiation shield Vacuum duct800 with radiation shield

  4. Production plan of LCGT mirror cryostats and peripheral components 2011 Jfy 2012 Jfy 2013 Jfy ‘11.3 ‘12.3 ‘13.3 ‘14.3 We are here Four Mirror Cryostats Manufacture components Transport to Kamioka Design by KEK Assemble and factory test with cryo-coolers Custody at Kamioka Bidding Cryo-cooler units Performance test Design by KEK 1st Prot-type Cryo-cooler unit test Transport to Kamioka Production of seven cryo-cooler units Performance test Custody at Kamioka Production of nine cryo-cooler units Duct shield units Production of Prot-type ducts shield units with cryo-coolers Design by KEK

  5. Requirements and Answers Basic requirements from LCGT cryogenic Answer to the requirements • Temperature of the test mass/mirror : 20 [K] • Inner radiation shield have to be cooled to < 8 K • The mirror have to be cooled without introducing • excess noise, especially vibration due to cryocoolers. • Easy access and enough capacity • to installation work around the mirror. • Satisfy ultra high vacuum specification < 10-7 Pa • Adopt Pulse Tube-type Cryo-cooler units • with very low vibration mount • based on the CLIO type cooler. • Adopt f2200 of inner diameter of flanges • for installation work of the mirror and suspension. • Analysed the cryostat response to • ground motion at Kamioka-mine. • Heat load from components as low as possible. • Develop very low out gas super insulation system for radiation heat load for ultra high vacuum • specification < 10-7 Pa

  6. Structure of Mirror Cryostat Cryostat accompany with four cryocooler units to SAS Cryostat Stainless steel t20mm Diameter 2.4m Height ~3.8m M ~ 10 ton Drawn by S. Koike (KEK) Remote valve View ports ~3.8m Low vibration cryocooler unit Main LASER beam Cryocoolers Pulse tube, 60Hz 0.9 W at 4K (2nd) 36 W at 50K (1st) Main beam (1200mm FL) 2.4m

  7. The interior of the cryostat Drawn by S. Koike (KEK) Support rods Double radiation shields with hinged doors View Ports Heat path to cryocooler

  8. Flame made by A6000 Aluminum Structure of Radiation Shields Secure stiffness and conductivity of the radiation shields Inner Shields Outer Shields

  9. Cryo-top Cryo-F Cryo-L Cryo-R Input Response to ground motion resonant frequency Y方向 X方向 X-direction Y-direction

  10. An Estimated Break Down List of Thermal Budget 1st Cold stage 2nd Cold stage • Outer Shield (W) • Eleven View Ports 22 • Radiation From 300 K 70 • Support post and Rods 24 • Electrical wires 3 x 10-4 • Total 116 • W/unit 29 • Inner Shield (W) • Duct Shields* < 0.05 • (Beam and SAS) • Eleven View Ports 0.4 • Radiation From 80 K 2.2 • Support post and Rods 2.4 • Electrical wires 3 x 10-4 • Mirror Deposition 0.9 • Scattering Light ? • Total 5.9 • W/unit 1.5 *Heat Load of Duct Shields will be told by Mr. Sakakibara

  11. Estimated Thermal Budget Estimated Heat Loads at the radiation shields and Support posts and rods 94 K at the top of the 80 K outer shield 70 W by the radiation at 80 K outer shield 2.2 W by the radiation at 8 K inner shield 7.4 K at the top of the 8 K inner shield 2.4 W by the radiation and conduction (support posts and tension rods) at 8 K Connection point with IM 24 W by the radiation and conduction (support posts and tension rods) at 80 K 47 K at 1st cold stage of Cryo-cooler 6.5 K at 2nd cold stage of Cryo-cooler dT1st = 26 K Very High Purity Aluminum Conductor (5N8) dT2nd=0.5 K Low Vibration Cryo-cooler unit

  12. Outline • Concept of the LCGT cryogenics • Structure and Response to • ground motion at CLIO/Kamioka mine • Thermal Budget of the cryostat • Estimation of heat load of the Mirror • from the beam duct shields • (by Mr. SAKAKIBARA) • Summary

  13. Estimation of heat load from the beam duct shieldsof the Mirror in the Cryostat • Thermal radiation from opening of 500 mm in diameter • Cooling power 3.6 W at 4 K (inner shield, 4 pulse tube cryo-coolers of 0.9 W at 4 K) • Thermal radiation appears to be reduced by reducing solid angle

  14. Problem experienced in CLIO • Thermal radiation reflected by metal shield pipe • Incident power (calculated using ray trace model, experimentally verified by T. Tomaru, et al. 2008 ) • Very large compared with solid angle mirror 300 K 4 K animation

  15. Reducing heat load by baffles • Incident power calculated using ray trace model by counting up number of reflections (Aluminum of A1070 measured at 10 mm, 100 K) 300 K 4 K animation

  16. Result of calculation R=0.94 R=0.94±0.02 Worse case R=0.96 P=52.4 mW Better case R=0.92 P=17.6 mW • The better result for the case that intervals of baffles are not equal to each other • If intervals of baffles are equal, ray whose angle passes through one baffle also passes • the other baffles mirror 300 K 4 K 16 x=0 m x=20 m

  17. Diamond Like Carbon coating DLC coating • Baffles whose room temperature sides are coated with DLC • Assuming reflectivity 0.35 (measured at 1 mm at room temperature by T. Tomaru, et al. 2005) • Preparation for measurement at 10 mm, cryogenic temperature is now underway Heat absorbed by baffles Heat load becomes smaller

  18. Summary 1 • Sum of heat load from openings of cryostat can be sufficiently reduced by baffles • 37 mW (18.4 mW x2) • Problem in CLIO solved • One prototype duct shield will be constructed until the end of March, 2013. • The duct shield will be tested to verify this calculation with the mirror cryostat.

  19. Summary 2 • The design of the mirror cryostat for LCGT satisfying requirements was almost finished. • The production of the components for the cryostat will be started after decided contractor. • Performance of the first cryostat will be demonstrated at the factory of the contractor on the mid of 2012 Jfy. We would like to discuss the detailed design process of the cryostat with participants of GWADW conference after this talk.

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