1. www.minigrail.nl Materials and Cooling Techniques G. Frossati, A.de Waard, L.Gottardi and O.Usenko Kamerlingh Onnes Laboratory Leiden, The Netherlands ESF exploratory workshop: Toward a 3 rd generation European Gravitational Wave Observatory Perugia, 21-23-Sept. 2005

2. www.minigrail.nl Sensitivity Minimum detectable energy T eff =T/  Q +2T N For a SQUID noise energy of one quantum Need  ~0.05; Q~2x10 6 : T~30 mK

3. www.minigrail.nl material properties Dissipation is mainly caused by the mobility of defects  defects freeze out at low temperature  Q-factor increases with reducing temperature

4. www.minigrail.nl H for several spheres

5. www.minigrail.nl MiniGRAIL Cryogenics; The dilution refrigerator still (700 mK) 50 mK plate mixing chamber (10 mK)

6. www.minigrail.nl MiniGRAIL Cryogenics

7. www.minigrail.nl Next: 33 ton sphere ? Project together with the Roma group to be submitted to INFN h QL ≈4x10 -24 /√Hz h QL ≈4x10 -23 /√Hz

8. www.minigrail.nl Cooling from 300K Fill liquid helium

9. www.minigrail.nl Forced flow MiniGRAIL 1.4 ton N 2 1200 L 600 L He SFERA 33 +7 ton 40000 N 2 20000 L He ! Use 4 GM cryocoolers For pre-cooling from 300K to 20K 4 PT410 for cooling to 4K and for the dilution refrigerator GM600 (Cryomech) 1200W at 250K PT400 60W at 60K and 1W at 4.2k Heat to remove ~70J/gm ~2.8x10 9 J Cool-down time ~2 weeks to 4k

10. www.minigrail.nl Liquid mixtures of 3 He and 4 He 0 0.5 0.250.751 2.0 1.5 1.0 3 He concentration T (K) Superfluid 3 He/ 4 He Normal 3 He/ 4 He -line Two-phase region

11. www.minigrail.nl Dilution Refrigeration as an upside-down evaporation VAPOR LIQUID 3 He out 3 He in diluted phase

12. www.minigrail.nl Dilution Refrigeration; Schematic view CIRCULATION SYSTEM  STILL  HEAT EXCHANGER  M IXING CHAMBER  HEAT ABSORPTION REGION 1k POT HEAT FLOW T MC

13. www.minigrail.nl Pulsed tube dilution refrigerator Joule Thompson heat exchanger replaces the 1K pot: No need for Helium bath JT Heat exchanger PTR Mixing Chamber 50K 4K 600 mK 60 mK 10 mK

14. www.minigrail.nl

17. Strain sensitivity 2m CuAl6% sphere  f=1000 Hz  f=100 Hz  f=10 Hz MiniGRAIL