1. Cryogenics for LCGT Technical Advisory Committee for LCGT 2005.08.23 ICRR SUZUKI, Toshikazu High Energy Accelerator Research Organization

2. contents Achievements of CLIO cryogenics Objects to be cooled and requirements Heat transfer Cryocoolers Design examples of LCGT cryogenics Summary

3. Achievements of CLIO cryogenics Cooling down Full operation of cryogenic system with dummy mirror installation. A small Ohmic heater simulates a laser absorption. Temperature of cryogenic parts are cooled down to their designed values. ( T.Uchiyama, Fig.11 in Chapter 11, Technical Report of LCGT )

4. Achievements of CLIO cryogenics Cryocooler system with sub-  m vibration 2nd V.R.Stage -> Heat Link Amplitude ≃ 50 nm Cold head -> Cryostat ≈ Seismic background

5. Achievements of CLIO cryogenics Vibration at 300K stage Red –PT Cryocooler:ON –Vacuum Pump :ON Blue –PT Cryocooler :OFF –Vaccuum Pump :OFF Cryocooler operation does not degrade seismic background at 300K stage. K.Yamamoto (Fig.12 in Chapter 11,Technical Report of LCGT)

6. Achievements of CLIO cryogenics Technology of cryocooler system with small vibration has been established. Cryocooler system can operate without affecting seismic background. Design of heat balance on cryogenic system was confirmed. CLIO Cryogenics --> LCGT Cryogenics Extend

7. Heat generation on the mirror T.Uchiyama,Technical Report of LCGT T=20 K q=290 mW ・ Design Safety factor Mirror substrate : Sapphire Suspension rods : Sapphire

8. Heat leaks from 300K to cryogenic parts Conduction from SAS Black body radiation from holes Conduction through support of shields Scattered Laser light Conduction through electric cablings Radiation to shields Heat Load of Cryocooler Heat Link Efficiency (T.Uchiyama, Fig.2 in Chap.11, Technical Report of LCGT)

9. Heat flow of LCGT cooling system (T.Tomaru, Fig.1 in Chap.13, Technical Report of LCGT ) 8 K 4.2 K

10. Estimation of heat flow (T.Tomaru, Fig.2 in Chap.13, Technical Report of LCGT )

11. Heat transfer in cryogenic GW detector Ultra-high vacuum –Conduction through solid Compatibility with vibration isolation –Large conductance for heat flow –Small conduction for mechanical vibration Small mechanical loss for mirror support Mirror Support : large , small mechanical loss, large strength From SPI to Cryocooler : large , small Young’s modulus From SAS to Platform : small , large strength

12. Material selection:Sapphire Sapphire is the only candidate for mirror support Size effect for thin rod (T.Tomaru) ( T.Uchiyama ) Type of carrier Specific heat Velocity of the carrier Mean free path

13. Material selection:Pure Al Material for heat links Avoid size effect for our purpose Inside cryostat -> single-wire Cryostat-cryocooler -> multi-wire (T.Tomaru, Fig.7in Chap.13, Tech. Rep. of LCGT) (T.Uchiyama, Fig.2 in Chap.12, Tech. Rep. of LCGT) 99.9999 % Al Example of pure Al wire 99.999% Al,  0.15 mm x 735

14. Material selection:amorphous metal SAS-Suspension platform Temperature gradient (300K-14K) Experience in the cryogenic resonant detector (60Hz)

15. Why cryocooler Intermittent charge Variation of temperature distribution Transportation of liquid Handling of evaporated gas Potential danger in deep tunnel Boiling noise Liquefaction facilities Stationary operation Stable distribution of temperature Electricity and cooling water Maintenance Mechanical vibration Cooling power Cryocooler Liquefied gas

16. Typical cryocoolers Cold stage~20  m Cold head~20 m/sec 2 Cold stage~20  m Cold head~0.2 m/sec 2 (T.Tomaru et al., Cryogenics, 44, ( 2004) 309-317 )

17. Cryocooler system for CLIO (T.Tomaru, Fig.3 in Chap.13, Tech. Rep. of LCGT)

18. Requirements for cryocoolers Heat load for LCGT cooling system Cooling power and numbers of cryocoolers (T.Uchiyama, Table 3 and 4 in Chap.11, Tech. Rep. of LCGT)

19. Increasing cooling power CLIO PT cryocooler 0.5 W @ 4.2 K 50 W @ 80 K LCGT cryocooler 1 W @ 4.2 K 100 W @ 80 K ◎ Compressor with larger capacity U=pV ○ Increasing nubmers of cryocoolers with current model ☆ Cryocooler with 1W@4.2K already exist1W@4.2K but not suitable for VRS type system. Target will be attainable within the extension of current technology.

20. Design example of LCGT cryostat

21. Example of cryostat location (T.Uchiyama, Fig.5 in Chap.11, Tech. Rep. LCGT)

22. Summary of LCGT cryogenics Fundamental technology of cooling system has been established. The PT cryocooler system of CLIO with low-level vibration have already satisfied the requirements of LCGT The way of increasing cooling power is attainable from current technology. Properties of key materials are known. Scale up from CLIO to LCGT is available.

23. Vac. Pump Compressor Connection of cold head and valve table