The Latest Status of the KAGRA Cryogenics

1. The Latest Status of the KAGRA Cryogenics N. KIMURAA, D. CHEN B, T. KUME A, S. KOIKE A, Y. SAKAKIBARA B, T. SUZUKI A, C. TOKOKU B, K. YAMAMOTO B, M. OHASHI B, and K. KURODA B A High Energy Accelerator Research Organization, KEK B ICRR, University of Tokyo,

2. Appendix Yusuke Sakakibara

3. Thermal Radiation Thermal Radiation Results • Experiment where SMALL plate is heated up to 300 K and BIG plate absorbs radiation was conducted • Heat transfer of left and right direction should be equal • Otherwise, even if two plates have same temperature, heat will be transferred Yusuke Sakakibara

4. Design of duct shield Optical lever • Pipe-shaped thermal radiation shield • Baffles are designed • Not to block out optical lever to sense tilt of mirror • To minimize thermal radiation onto mirror • Three sections are cooled down independently by three cryocoolers • Cryocooler for section 2 was not operated Length in mm 17 m Yusuke Sakakibara

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

6. Estimated Thermal Budget 80 W by the radiation at 80 K outer shield 94 K at the top of the 80 K outer shield 9 K at the top of the 8 K inner shield 2.0 W by the radiation at 8 K inner shield Connection point with IM 0.3 W by the radiation and conduction (support posts and tension rods) at 8 K 53 K at 1st cold stage of Cryo-cooler 7.6 W by the radiation and conduction (support posts and tension rods) at 80 K 7.1 K at 2nd cold stage of Cryo-cooler dT1st = 17 K dT2nd=1.5 K Very High Purity Aluminum Conductor (5N8) Low Vibration Cryo-cooler unit

7. Requirement and Answer Requirements for KAGRA cryogenics Satisfy the requirements for the Cryogenics • Temperature of the test mass/mirror < 20 [K] • Inner radiation shield have to be cooled to < 8 K • The test mass have to be cooled without introducing • excess noise, especially vibration due to cryocoolers. • Easy access and enough capacity • to installation work around the mirror. • Allowable size as large as possible under public transport regulation and KAGRA tunnel. • 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. • Analyzed 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 • radiative heat load but also useable • under ultra high vacuum < 10-7 Pa

8. Low Vibration Cryo-cooler Unit Cooling Power ・> 2.5W@9K ( at connection point of 8 K conduction bar) ・> 35W@70K ( at connection point of 80 K conduction bar) Vibration Characteristics ・< ±100 nm ( at connection point of 8 K conduction bar) ・< ±100nm ( at connection point of 80 K conduction bar) Photo: Performance test at ICRR Base on CLIO type Cryo-cooler with low vibration mount for KAGRA but cooling power is lager than CLIO

9. Structure view of the Low Vibration Cryo-cooler Unit Valve Unit Bellows Flexible Heat Links バルブ台 1m Part of Vibration Reduction Stage 5N8 8K Conduction Bar Support Frame (Support: Cold Head) 80K Cooling passage Vacuum Vessel (Support: Conduction Paths) 2m

10. Performance of the low vibration cryo-cooler unit Vibration at the connection point To suppress the vibration at 1.7 Hz below 0.1 μm/Hz^0.5, we improved on the support structure design. • We measured the vibration of sixteen cryocooler units. • We confirmed its vibration reduction ratio lager than 100 and less than 0.1 μm/Hz^0.5. • Cooling powers of 2.5W@9K and 35W@70K were also confirmed too. Impulse response of unit 14 Courtesy by Dr. C. TOKOKU Presented at CEC/ICMC2013, 2EPoE1-03, Anchorage, USA (2013).

11. Cooling Scheme of the mirror • Heat transferred via pure aluminum heat links. We need Φ1 mm, L=1 m heat links x 7~8 Thermal simulationDone by Y. Sakakibara GWADW 2012

12. Cooling Time Reduction with DLC To increase cool down by radiation, form black coating with Diamond Like Carbon on outer surface of the payload and inner surface of 8K shield. Items Materials Mass Platform Without DLC RM for IM With DLC Almost half ! IM TM Comparison of Cooling Time with & without DLC RM TM : Test Mass RM : Recoil Mass IM : Intermediate Mass Courtesy by Y. Sakakibara S.Koike 12 12

13. Half Size Dummy Cryo-payload Experiment with KAGRA cryostats • 1/2 size dummy payload was suspended inside cryostat No.3 • Thermal radiation was examined (without any heat links) • Cooling from room temperature Spare of CLIO mirror Model Payloads designed and made byR. Kobayashi, S. Koike (KEK) 2013.6.24 CEC/ICMC (Anchorage, Alaska) Yusuke Sakakibara

14. Results • Effect of High Emissivity Coating for Cooling Time of the Payload is • Confirmed. Consistent with calculation! Emissivity Sapphire: 0.5 Platform: 0.3*(T/300K) IM: 0.4*(T/300K) 2013.6.24 CEC/ICMC (Anchorage, Alaska) Yusuke Sakakibara

15. Cooling test in Toshiba Heat Load Response Test Heater and thermometer Pulse tube cryocoolers Pulse tube cryocoolers Sapphire mirror Pulse tube cryocoolers 15 15 15 15 15

16. Cooling test in Toshiba Result of Heat Load Response @ 8K Radiation Shield Mirror Operation 5 W ~ 12.5 ppm 10 W ~25 ppm 2 W~ 5 ppm 0 W ~0 ppm It is confirmed that 25 ppm (10 W) @400 kW of scattered loss is acceptable as heat load for the cryocoolers via the 8 K radiation shield. Scatted light power is 4 W @400 kW beam power when scattered loss on the mirror surface is 10 ppm. 16 16 16 16 16