1. Nawrodt 05/2010 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. Nawrodt 05/2010 Overview Motivation Material Properties –thermal properties –mechanical properties Thermal Noise Issues for ET Summary GWADW2010 Kyoto/Japan #2/54

3. Nawrodt 05/2010 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 #3/54

4. Nawrodt 05/2010 Material Properties – Thermal Conductivity in Crystals GWADW2010 Kyoto/Japan 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) #4/54

5. Nawrodt 05/2010 Material Properties – Thermal conductivity of Silicon experimental results (double-log scale!): “recommended curve” (< 10 14 cm -3 boron, approx. 1 mg B in 1 t Si) increasing impurity concentration (scattering of phonons on impurities) smaller structures + impurities (~ 1/L term) see Callaway 1961 or Casimir 1938 [Touloukian] GWADW2010 Kyoto/Japan #5/54

6. Nawrodt 05/2010 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) Material Properties – Thermal conductivity of Silicon GWADW2010 Kyoto/Japan #6/54

7. Nawrodt 05/2010 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)] Material Properties – Thermal conductivity of Silicon GWADW2010 Kyoto/Japan #7/54

8. Nawrodt 05/2010 Mechanical Properties – Mechanical Loss of Materials GWADW2010 Kyoto/Japan #8/54

9. Nawrodt 05/2010 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 #9/54

10. Nawrodt 05/2010 Mechanical Properties – Impurities imperfection in crystals can change their states (moving, rotation, …) example: crystalline quartz (SiO 2 ) modelled as double well potential GWADW2010 Kyoto/Japan view along the c-axis O Si E energy position “Debye-peak” thermally activated transition #10/54

11. Nawrodt 05/2010 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 meltfrom solid Czochralski-processFloating-Zone-process O-concentration: 10 18 cm -3 O-concentration: 10 14 cm -3max. dia. in some years ~ 45 … 50 cm~ 30 … 35 cm GWADW2010 Kyoto/Japan #11/54

12. Nawrodt 05/2010 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 #12/54

13. Nawrodt 05/2010 Mechanical Properties – Mechanical loss in solids GWADW2010 Kyoto/Japan crystalline quartzsilicon impurities could be indentified to be alkaline ions from the growing process origin of most of the peaks unclear (blue – oxygen in silicon) #13/54

14. Nawrodt 05/2010 Mechanical Properties – Mechanical loss in solids GWADW2010 Kyoto/Japan #14/54

15. Nawrodt 05/2010 Thermal Noise – Bulk Material GWADW2010 Kyoto/Japan Thermo-elastic noise: Brownian thermal noise: [Liu, Thorne 2000] [Braginsky 1999] [Liu, Thorne 2000] [Liu, Thorne 2000, Bondu, Hello, Vinet 1998] #15/54

16. Nawrodt 05/2010 Thermal Noise - Coating GWADW2010 Kyoto/Japan Thermo-elastic noise: Brownian thermal noise: [Harry et al. 2002] [Braginsky, Fejer et al. 2004] note: for the coating Brownian noise the substrate‘s Young‘s modulus is important #16/54

17. Nawrodt 05/2010 Thermal Noise – Crystal Orientation GWADW2010 Kyoto/Japan [Wortman, Evans, J. Appl. Phys. 36 (1965)] Selection of the crystal orientation for low noise performance: [e.g. Liu, Thorne 2000] 2 extreme values for the Young’s moduli of Si: Y min = 130 GPa for Si(100) Y max = 188 GPa for Si(111) e.g. bulk Brownian noise: #17/54

18. Nawrodt 05/2010 Thermal Noise - Overview GWADW2010 Kyoto/Japan 20 K 300 K Si(111) test mass, dia. 50 cm, thickness 30 cm, HR stack (20 doublets, Ta 2 O 5 :TiO 2, SiO 2 ) #18/54

19. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 5 K #19/54

20. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 8 K #20/54

21. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 10 K #21/54

22. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 12 K #22/54

23. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 14 K #23/54

24. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 16 K #24/54

25. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 18 K #25/54

26. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 20 K #26/54

27. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 22 K #27/54

28. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 24 K #28/54

29. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 26 K #29/54

30. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 28 K #30/54

31. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 30 K #31/54

32. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 40 K #32/54

33. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 50 K #33/54

34. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 60 K #34/54

35. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 70 K #35/54

36. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 80 K #36/54

37. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 90 K #37/54

38. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 100 K #38/54

39. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 110 K #39/54

40. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 115 K #40/54

41. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 120 K #41/54

42. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 125 K #42/54

43. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 130 K #43/54

44. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 140 K #44/54

45. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 150 K #45/54

46. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 200 K #46/54

47. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 250 K #47/54

48. Nawrodt 05/2010 Thermal Noise – Temperature Dependence GWADW2010 Kyoto/Japan 300 K #48/54

49. Nawrodt 05/2010 Thermal Noise – Adding Suspension GWADW2010 Kyoto/Japan Thermal bath „Universe“ TM 5 m  = 10 -4 1 m, dia. 3 mm  = 2×10 -9 300 K 5 K 20 K [S. Hild] 10 km simplified layout (4 suspended masses): suspension loss (lowest stage): #49/54

50. Nawrodt 05/2010 Thermal Noise – Adding Suspension GWADW2010 Kyoto/Japan Thermal bath „Universe“ TM 5 m  = 10 -4 1 m  = 2×10 -9 300 K 5 K 20 K sensitivity goal can be reached, additional „help“ is needed at low frequencies (artificial lowering of pendulum frequency needed – actively/passivly) #50/54

51. Nawrodt 05/2010 Cooling Issues through the suspension cooling through fibre target temperature: below 22 K thermal bath: –technically limited to 2-5 K –no huge advantage to go for 2 K from a thermal conductivity point of view (limitation through geometry, low thermal conductivity at T < 10 K) –however, 2 K allows use of suprafluid helium with much reduced mechanical disturbances GWADW2010 Kyoto/Japan #51/54

52. Nawrodt 05/2010 Cooling Issues through the suspension maximum cooling power is very low (L = 1m, T bath = 2 K, 4 fibres) GWADW2010 Kyoto/Japan T mirror [K]Diameter [mm]P max [mW] 203480 51300 83400 153270 5740 81900 103100 5270 8690 #52/54

53. Nawrodt 05/2010 Cooling Issues through the suspension highest possible thermal conductivity needed investigation optical absorption in silicon (at 1550 nm unknown) strong reduction of introduced thermal load needed –reduction of incident laser power (Xylophon concept, 2 detectors, low frequency detector with low laser power e.g. 18 kW) –very carefull dealing with scattered light needed (additional heating of test masses) GWADW2010 Kyoto/Japan [Hild et al. 2010] #53/54

54. Nawrodt 05/2010 Conclusion crystalline materials are candidate materials for 3rd generation detectors cooling necessary to reduce thermo-elastic noise high thermal conductivity is used to extract heat, however minimum thermal load should have very high priority (scatter!) thermal noise can be reduced below the requirements with reasonable materials (silicon) and R&D (loss measurments, optics absorption, coating research,…) GWADW2010 Kyoto/Japan #54/54