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, Sept. 2005

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

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

H for several spheres

MiniGRAIL Cryogenics; The dilution refrigerator still (700 mK) 50 mK plate mixing chamber (10 mK)

MiniGRAIL Cryogenics

Next: 33 ton sphere ? Project together with the Roma group to be submitted to INFN h QL ≈4x /√Hz h QL ≈4x /√Hz

Cooling from 300K Fill liquid helium

Forced flow MiniGRAIL 1.4 ton N L 600 L He SFERA ton N 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

Liquid mixtures of 3 He and 4 He He concentration T (K) Superfluid 3 He/ 4 He Normal 3 He/ 4 He -line Two-phase region

Dilution Refrigeration as an upside-down evaporation VAPOR LIQUID 3 He out 3 He in diluted phase

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

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

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