Thermal noise and material issues for ET

1. Thermal noise and material issues for ET Ronny Nawrodt Matt Abernathy, Nicola Beveridge, Alan Cumming, Liam Cunningham, Giles Hammond, Daniel Heinert, Jim Hough, Iain Martin, Peter Murray, Stuart Reid, Sheila Rowan, Christian Schwarz, Paul Seidel, Marielle van Veggel GWADW2010 Meeting, Kyoto 20/05/2010 Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena Sonderforschungsbereich Transregio 7 „Gravitationswellenastronomie“ Institute for Gravitational Research, University of Glasgow Einstein Telescope Design Study, WP2 „Suspension“

2. Overview • Motivation • Material Properties • thermal properties • mechanical properties • Thermal Noise Issues for ET • Summary GWADW2010 Kyoto/Japan

3. Motivation • ET will need a radical change in the materials in order to achieve the sensitivity goals: • suspensions, • test mass materials, • coatings, • optical materials • Additionally, going towards cryogenics temperatures will dramatically change material properties  additional degree of freedom. • The new material has to be compared to the best optical material currently available at room temperture! GWADW2010 Kyoto/Japan

4. Material Properties – Thermal Conductivity in Crystals • typically 3 zones: • higher temperatures: TC is limited by phonon-phonon scattering • lower temperatures: mean free path of phonons increases, scattering at impurities becomes important • high purity samples: at very low temperatures the sample geometry becomes important (scattering of phonons at the sample surface  limitation of TC) GWADW2010 Kyoto/Japan

5. Material Properties – Thermal conductivity of Silicon experimental results (double-log scale!): increasing impurity concentration (scattering of phonons on impurities) “recommended curve” (< 1014 cm-3 boron, approx. 1 mg B in 1 t Si) smaller structures + impurities (~ 1/L term) see Callaway 1961 or Casimir 1938 [Touloukian] GWADW2010 Kyoto/Japan

6. Material Properties – Thermal conductivity of Silicon • in high purity silicon the different silicon isotopes take the role as scatter centers (-> impurities) • natural Si has 3 stable isotopes: • 92% Si-28 • 5% Si-29 • 3% Si-30 • they cause small local changes in the lattice due to their different atom masses  effect is small • however, concentration is very large compared to typical impurity concentrations (ppm range) GWADW2010 Kyoto/Japan

7. Material Properties – Thermal conductivity of Silicon • it is possible to enrich/purify silicon • isotopic pure silicon shows a much larger thermal conductivity in the peak region compared to standard semiconductor grade silicon • 99.8% Si-28: TC ~ 10x larger • disadvantage: price ~ 1000 US$/g semiconductor grade ~ 500 US$/kg [Ruf et al., Solid State Comm. 115 (2000)] GWADW2010 Kyoto/Japan

8. Mechanical Properties – Mechanical Loss of Materials GWADW2010 Kyoto/Japan

9. Mechanical Properties – Surface loss • sudden change of chemistry at the surface  end of periodicity of crystal lattice  remaining defect in perfect single crystals • it was shown that the surface loss can be influenced by proper treatments (heating, passivation, etc.) • however, most of these changes are not stable and the surface loss gets back to the initial level after hours GWADW2010 Kyoto/Japan

10. E energy position Mechanical Properties – Impurities • imperfection in crystals can change their states (moving, rotation, …) • example: crystalline quartz (SiO2) modelled as double well potential view along the c-axis “Debye-peak” Si O thermally activated transition GWADW2010 Kyoto/Japan

11. Mechanical Properties – Impurities in Silicon • doping concentration is variable  lowest possible value will used • most serious impurity in Si is oxygen from the growing process (electronically not active  nearly no support from semiconductor industry!) • two growing processes: from melt from solid Czochralski-process Floating-Zone-process O-concentration: 1018 cm-3 O-concentration: 1014 cm-3 max. dia. in some years max. dia. in some years ~ 45 … 50 cm ~ 30 … 35 cm GWADW2010 Kyoto/Japan

12. Mechanical Properties – Phonon-Phonon-Interaction • fundamental process in crystalline solids  cannot be avoided • two mechanisms: • high temperatures / high frequencies direct interaction of one phonon with another one (Landau-Rumer-process) • low temperatures / low frequencies elastic mode (low frequency phonon) changes the lattice  change of the equlibrium distribution of phonons  redistribution needs energy  loss (Akhiezer-process) GWADW2010 Kyoto/Japan

13. Mechanical Properties – Mechanical loss in solids crystalline quartz silicon impurities could be indentified to be alkaline ions from the growing process origin of most of the peaks unclear (blue – oxygen in silicon) GWADW2010 Kyoto/Japan

14. Mechanical Properties – Mechanical loss in solids GWADW2010 Kyoto/Japan

15. Thermal Noise – Bulk Material • Thermo-elastic noise: • Brownian thermal noise: [Braginsky 1999] [Liu, Thorne 2000] [Liu, Thorne 2000] [Liu, Thorne 2000, Bondu, Hello, Vinet 1998] GWADW2010 Kyoto/Japan

16. Thermal Noise - Coating • Thermo-elastic noise: • Brownian thermal noise: [Braginsky, Fejer et al. 2004] [Harry et al. 2002] note: for the coating Brownian noise the substrate‘s Young‘s modulus is important GWADW2010 Kyoto/Japan

17. Thermal Noise – Crystal Orientation Selection of the crystal orientation for low noise performance: e.g. bulk Brownian noise: [e.g. Liu, Thorne 2000] 2 extreme values for the Young’s moduli of Si: Ymin = 130 GPa for Si(100) Ymax = 188 GPa for Si(111) [Wortman, Evans, J. Appl. Phys. 36 (1965)] GWADW2010 Kyoto/Japan

18. Thermal Noise - Overview 300 K 20 K Si(111) test mass, dia. 50 cm, thickness 30 cm, HR stack (20 doublets, Ta2O5:TiO2, SiO2) GWADW2010 Kyoto/Japan

19. Thermal Noise – Temperature Dependence 5 K GWADW2010 Kyoto/Japan

20. Thermal Noise – Temperature Dependence 8 K GWADW2010 Kyoto/Japan

21. Thermal Noise – Temperature Dependence 10 K GWADW2010 Kyoto/Japan

22. Thermal Noise – Temperature Dependence 12 K GWADW2010 Kyoto/Japan

23. Thermal Noise – Temperature Dependence 14 K GWADW2010 Kyoto/Japan

24. Thermal Noise – Temperature Dependence 16 K GWADW2010 Kyoto/Japan

25. Thermal Noise – Temperature Dependence 18 K GWADW2010 Kyoto/Japan

26. Thermal Noise – Temperature Dependence 20 K GWADW2010 Kyoto/Japan

27. Thermal Noise – Temperature Dependence 22 K GWADW2010 Kyoto/Japan

28. Thermal Noise – Temperature Dependence 24 K GWADW2010 Kyoto/Japan

29. Thermal Noise – Temperature Dependence 26 K GWADW2010 Kyoto/Japan

30. Thermal Noise – Temperature Dependence 28 K GWADW2010 Kyoto/Japan

31. Thermal Noise – Temperature Dependence 30 K GWADW2010 Kyoto/Japan

32. Thermal Noise – Temperature Dependence 40 K GWADW2010 Kyoto/Japan

33. Thermal Noise – Temperature Dependence 50 K GWADW2010 Kyoto/Japan

34. Thermal Noise – Temperature Dependence 60 K GWADW2010 Kyoto/Japan

35. Thermal Noise – Temperature Dependence 70 K GWADW2010 Kyoto/Japan

36. Thermal Noise – Temperature Dependence 80 K GWADW2010 Kyoto/Japan

37. Thermal Noise – Temperature Dependence 90 K GWADW2010 Kyoto/Japan

38. Thermal Noise – Temperature Dependence 100 K GWADW2010 Kyoto/Japan

39. Thermal Noise – Temperature Dependence 110 K GWADW2010 Kyoto/Japan

40. Thermal Noise – Temperature Dependence 115 K GWADW2010 Kyoto/Japan

41. Thermal Noise – Temperature Dependence 120 K GWADW2010 Kyoto/Japan

42. Thermal Noise – Temperature Dependence 125 K GWADW2010 Kyoto/Japan

43. Thermal Noise – Temperature Dependence 130 K GWADW2010 Kyoto/Japan

44. Thermal Noise – Temperature Dependence 140 K GWADW2010 Kyoto/Japan

45. Thermal Noise – Temperature Dependence 150 K GWADW2010 Kyoto/Japan

46. Thermal Noise – Temperature Dependence 200 K GWADW2010 Kyoto/Japan

47. Thermal Noise – Temperature Dependence 250 K GWADW2010 Kyoto/Japan

48. Thermal Noise – Temperature Dependence 300 K GWADW2010 Kyoto/Japan

49. 10 km [S. Hild] Thermal Noise – Adding Suspension simplified layout (4 suspended masses): „Universe“ 300K • 5 m • = 10-4 Thermal bath 5 K suspension loss (lowest stage): • 1 m, dia. 3 mm • = 2×10-9 TM 20 K GWADW2010 Kyoto/Japan

50. Thermal Noise – Adding Suspension „Universe“ 300K • 5 m • = 10-4 Thermal bath 5 K • 1 m • = 2×10-9 TM 20 K sensitivity goal can be reached, additional „help“ is needed at low frequencies (artificial lowering of pendulum frequency needed – actively/passivly) GWADW2010 Kyoto/Japan