G.W. Interferometers & Cryogenics ILIAS -STREGA: task C1

1. G.W. Interferometers&CryogenicsILIAS -STREGA: task C1 Fulvio Ricci Dipartimento di Fisica, Università di Roma La Sapienza & I.N.F.N. Sezione di Roma Fulvio Ricci ILIAS

2. Cooling mirrors: the task C1 Cryogenic Payload Design Cooling configuration study: -experimental test -computer simulation Refrigeration system study: The cryogenic facility: - Vibration Free Cryostat (V.F.C.) Cryogenic Instrumentation for the monitor and control low frequency accelerometer high frequency accelerometer displacement sensor Fulvio Ricci ILIAS

3. Cryogenic Payload Design Cooling configuration study: -experimental test -computer simulation Fulvio Ricci ILIAS

4. Operation of the Cryomech PTR Cold head of the Pulse Tube Refrigerator\ From Cryomech Thermal shields and vacuum chamber of the PTR cryostat PTR ready for cooling Fulvio Ricci ILIAS

5. Cooling with PTR the CaF2 mirror sample Diameter 100 mm Thickness 30 mm Suspended using four thin (0.4 mm) copper wire (electrolytic grade) The heat is extracted through the suspension Fulvio Ricci ILIAS

6. Experimental Data I stage Extracted Power = 0 II stage Extracted Power = 0 Fulvio Ricci ILIAS

7. Finite Element Simulation of the system • Material properties vs temperature: • Copper screens (gold coated), CaF2 mirror • copper wires, • Residual thermal inputs • Thermal boundary resistance • Refrigeration Power Typical value for metal-dielectric contact From measurements Fulvio Ricci ILIAS

8. Thermal properties vs temperature Fulvio Ricci ILIAS

9. Boundary conditions: definition of the heat flows • The extracted powers at each stage depend on both the temperatures of the stages themselves. Fulvio Ricci ILIAS

10. Thermal load & thermal gradients Fulvio Ricci ILIAS

11. Fulvio Ricci ILIAS

12. Cryogenic facility developmentRefrigeration system study: Vibration Free Cryostat (V.F.C.) Fulvio Ricci ILIAS

13. Cool down without liquid helium: the Pulse Tube Cryocooler • A Pulse Tube Refrigerator (PTR) or "G-M style" pulse tube cryocooler, is a variant of a Gifford-McMahon (GM) cryocooler. • PTR operate at low frequencies, typically <5 Hz. • Used a conventional oil-flooded G-M compressor and a valve set near the cold head to convert the continuous flow of helium to a low frequency pressure wave. First stage Second stage • Suitable for applications that require efficient operation: • No moving parts in cold head. Minimal vibration, low acoustic noise, reliability. • High efficiency: 2 to 3 times higher efficiency than GM cryocoolers for loads temperatures between 55 and 120 K. Fulvio Ricci ILIAS

14. The simpler solution • Passive vibrational isolation system for the heat link • Long heat link • Part of the refrigerating power absorbed by the isolators • Attenuation of the refrigerating power Fulvio Ricci ILIAS

15. Spring Our solution: the Vibration Free Cryostat • Active vibrational isolation system for the heat link • Shorter heat link • Refrigerating power preserved It is necessary to monitor the vibration at low temperature and to act refrigerator: • Accelerometers and position sensing devices; • Actuators; V.F.C. Fulvio Ricci ILIAS

16. V.F.C. Sumitomo cryocooler Cooling capacity 1st stage 10W/20W @ 45 K (50/60 Hz) 2nd stage 0.5W/0.5W @ 4.2 K (50/60 Hz) Lowest temperature <0.3 K Fulvio Ricci ILIAS

17. Displacement noise of the cold stage Sensor noise Vertical displacement Horizontal displacement Fulvio Ricci ILIAS

18. Vibration Free Cryostat: first mechanical assembling V.F.C. Fulvio Ricci ILIAS

19. V.F.C. 3 2 1 4 The springs and skeleton The Al inner vacuum chamber The model of the gelly fish for thermal contact 4) The special bellow Fulvio Ricci ILIAS

20. Work in progress • PT Refrigeration system : set up of the vibration compensation system. • mechanical transfer function measurements • - noise characterization to be completed in the low frequency region • -filter design • The PT Refrigeration system will be used to study the thermal properties of the materials candidates for the mirrors of a cryogenic interferometer and also of the e.m. actuators which can be used at low temperatures. Fulvio Ricci ILIAS

21. Cryogenic Instrumentation for the monitor and control- capacitive accelerometer for low frequency range- accelerometer for high frequency capacitive piezo-displacement sensor Fulvio Ricci ILIAS

22. Elastic beams Moving plate Fixed plate High frequency accelerometer Capacitive transducer With one vibrating plate ft ~ 2 kHz Vbias = 450 Volt Ct ~ 800 pF Gap ~ 80 mm Room temperature calibration by means of a B&K pz-accelerometer Low frequency cut-off ~10 Hz limited by the low input impedance of the voltage amplifier (~20 MW) Fulvio Ricci ILIAS

23. Acceleration Noise Frequency [Hz] Fulvio Ricci ILIAS

24. Vibration measurements performed on the CRYOMECH refrigeratorcold stage with piezo-accelerometers at low temperature • Sharp peak at 1.4Hz due to the gas pulse in the cold stage • Total displacement higher than the measurement on the Sumitomo PT. • T. Tomaru et al. Cryogenics, 44 (2004) • High frequency displacement structure probably due to the resonance of the cryostat Fulvio Ricci ILIAS

25. Accelerometer built in Pisa (A. Bertolini, R. De Salvo, F. Fidecaro A . Takamori : IEEE Trans. in preparation) and…….cooled in Roma Accelerometer for very low frequency range (Characteristic frequency 0.5 Hz) Fulvio Ricci ILIAS

26. Monitor of the resonance frequency of the accelerometer. Her Q is limited by recoil effect of its support Fulvio Ricci ILIAS

27. Photodiode Target Laser Position sensor : the optical fiber bundle Material: optran silica for broad temperature range Protection: PVC or s.s. Laser source : 638 nm Target: polished surface Fulvio Ricci ILIAS

28. Conclusions • -Payload Design: we are tuning the ANSYS simulation program.We need to move it on a farm. • Experimental activity: thermal data collection • Cancellation of the extra-noise vibration associated to the cooling system: first mechanical assembly of the Vibration Free Cryostat • -Cryogenic Instrumentation: tests at cryogenic temperatures. Fulvio Ricci ILIAS