1. Thermal Noise Workshop February 23rd, 2012 Paola Puppo – INFN Roma

2. * Motivations * Losses characterization * Quality factors * Suspensions: pendulum and violin modes * Mirrors * Thermal noise curve prediction * Conclusions 2

3. 3

4. * Mirror suspensions wires: * steel wires (c85) (  = 1.9 10 -4 ) * Mirror substrate: * IN suprasil 312 (  =10 -9 ) * OUT herasil (  =1.3 10 -6 ) * Coating: Ta 2 O 5 * Mirror suspensions wires: * SiO2 wires (  = 3.3 10 -8 ) * Mirror substrate: * IN suprasil 312 (  =10 -9 ) * OUT suprasil (  =10 -9 ) * Coating: Ti:Ta 2 O 5 Thermal Noise Contributions Mechanical Losses 4 Main parameters for the dissipations of mirrors and suspensions in Virgo+ and Virgo+MS. Data taken from VIR-0639D-09 and VIR-NOT-PER-1390-51.

5. Substrate Thermal Coating Thermal Pendulum Thermal * VIR-0639D-09 + Test Mass Thermal 5

6. 6

7. 7 Parts of a monolithic payload: a)Mirror with ears b)Fiber with upper clamp and anchor, c)Lower clamp, d)Upper clamp. e)Marionette f)Reaction Mass (e) (f)

8. 8 33 22 11 M3M3 M2M2 M1M1 M 1 marionette M 2 mirror M 3 recoil mass (The mirror last stage suspension as a branched system) [*] Bernardini A., Majorana E.,Puppo P.,Rapagnani P., Ricci F., Testi G. "Suspension last stages for the mirrors of the Virgo interferometric gravitational wave antenna." Rev. Sci. Instr. 70, no. 8 (1999): 3463. M1M1 M2M2 M3M3 Pendulum Thermal Noise Model

9. 9 Structural Dissipations Thermoelastic Dissipations Surface Losses Different types of internal losses in the branched pendulum model Wire standoffs Pendulum Dilution Factor

10. 10 June 26th, 2007 INFN 10 Example: branched pendulum Virgo-like: Upper pendulum 110 kg (Q=50) Recoil mass 50 kg (Q=10 5 ) Mirror 21 kg ( very low losses  monolithic suspensions) In presence of low dissipative mirror suspensions, the contributions of the other last stage suspension elements to thermal noise of the mirror cannot be neglected. A new thermal noise estimation must be done by including the viscous and internal dissipations of the marionette and recoil mass pendulum. [*] VIR-015C-09, F. Piergiovanni, M. Punturo and P. Puppo, The thermal noise of the Virgo+ and Virgo Advanced Last Stage Suspension (The PPP effect).

11. 11 P. Puppo, Proceedings of the Twelfth Marcel Grossmann Meeting on General Relativity Paris, France 2009

12. 12

13. 13 * Saulson & Gonzalez, J. Acoust. Soc. Am., 96, July 1994 (*) * Violin modes can be used to estimate the wire losses: * From the first violin Q we have an estimation of the wire loss angle and we extrapolate it at the pendulum frequency * From the pendulum modes Q we can yield informations on the losses of the Marionette and the Reaction Mass pendula. Silica wire losses characterization

14. 14 Q Measurement of the Violin Modes * VIR- 0031A -11 Frequency Q 10 8 10 5 NI WENE WI

15. 15 Violin energy leak through coupling with clamps/marionette? Frequency of violin (Hz) Q of violin Q of lossy mode marionette =3500 Hz (Tortional  x ) lossy  wire  2.3 10 -7  marionette  2.3 10 -5 See also M. Tacca talk

16. 16

17. 17 Q of the Pendulum Modes Excitation by Recoil Mass Coils

18. 18 Summary of the losses obtained from the violin and pendulum losses using the branched model The measured pendulum Q’s are dominated by the losses of the RM. However the recoil effect of the reaction mass is only dominant at resonance; The thermal noise of the mirror pendulum above 10 Hz is not affected and depends only on silica losses.

19. 19

20. Levin Formula (*) (*) In GWINC: For W tot Equation references to Bondu, et al. Physics Letters A 246 (1998) 227-236 (**) A. Gillespie and Raab, Physical Review D, 52 (1995) 577. Modal Expansion Formula (**) 20

21. Including Viscous losses of the modes 21

22.  =  Structural vs Viscous Dissipations:  =  bbbb aaaa Viscous Damping Internal Damping 22

23. 23 From Q measurements to loss factors Strain Energies Evaluated at the resonances with FEA

24. (*) Logbook entries: 29903, 29856, 29748, 28456,27518 (**)(VIR-NOT-ROM-1390-262)(VIR-0556A-10) (***) A. Colla, The NoEMi (Noise Event MIner) Framework, Proc.of the Amaldi 9 th, July 2011 Mirrors Thermal noise

26. Behavior of Q with frequency of the modes 26 Hz FEM will be used to understand these results

27. 27 * We used the Q measurements to infer the loss angles of each mirror. * The hypotheses are the following: Assume frequency independent structural dampings; Use the highest Q mode to evaluate the overall structural losses; Use the lowest Q mode to estimate either a possible viscous damping acting on that mode or an energy leak due to coupling with other modes.

28. 28 FEA of the mirrors (1) INPUTEND Thickness 100 mm Diameter 350 mm Flats height 50 mm100 mm Material Properties ρ=2200 kg/m 3 Y=72.3 GPa σ=0.17 Flats height 50 mm100 mm Coating Ears & Anchors IN END Ears & Anchors Coatings Coating Diameter 200 mm330 mm Material Properties high index material (Ta 5 O 2 ) ρ=2200 kg/m 3 Y=72.3 GPa σ=0.17 Material Properties low index material (SiO 2 ) ρ=2200 kg/m 3 Y=140 GPa σ=0.26 High Index Thickness 0.956 μm2.393 μm High Index Loss angle 5 10-5 Low Index Thickness 2.388 μm4.1086 μm Low Index Loss angle 2 10-4

29. 29 FEA of the mirrors (2) Ears Silicate Bonding Thickness 60 nm Silicate Bonded Area 2×18 cm 2 Material Properties ρ=2200 kg/m 3 Y=7.9 GPa σ=0.17 Loss Angle 0.1 Anchors Water Glass Area 4×3 cm 2 Material Properties ρ=2200 kg/m 3 Y=1.9 GPa σ=0.17 Loss Angle * Thickness μm0.1 ;0.5 ;1.0

30. 30 FEA of the mirrors (results)  WG *s WG =0.5  m

31. 31 NI (10 6 )WI (10 6 )NE (10 6 )WE (10 6 ) Measured FEMMeasured FEM Butterfly (X) 0.57115.2142.13.611 Butterfly (+) 1224.3178.3315.311 Drum 0.34-0.300.041731.7213 Butterfly (\) 0.9441.713.82.340.053.9 Butterfly (|) 5.1210.496.45 6.6

32. 32 Thermal Noise using structural loss factors yielded by FEA and measured Q

33. 33 AdV Thermal Noise

34. Lowest Q modes study (viscous or coupling?) 34 Freq [Hz] Drum1 Q of drum1 (10 6 ) Freq [Hz] Drum1 Freq [Hz] Drum2 Q of drum2 (10 6 ) Comment 5671 5676 0.34 0.30 5671 5676 156730.204 Viscous?- Coupling 56420.045642156590.192Viscous? 57203 157730.08Not Viscous 56991.75699157631.49Viscous? If they are viscous from drum1 and drum2 holds  Effective masses Drum1 (Hz) Drum1 (kg) Drum2 (Hz) Drum2 (kg) Input56507.7156002.9 End57009.6158005.4 (*) (*) K. Yamamoto, PhD Thesis, Univ. of Tokyo (2000).

35. Why the Low Q? The NI Drum mode case XIII violin – NI drum mode degeneracy The lower Q dominates - + 35 P. Rapagnani: Il nuovo Cimento v5, n4, 1982, p385 35

36. 36   Normal Modes 8/11/2011 Piero Rapagnani

37. 37 Mode Coupling changes the damping only at resonance

38. The theoretical prediction is computed using the measured intrinsic Q’s of the violin and of the NI drum The Lorentian fits results are in agreement with the expected thermal amplitudes and the measured Q’s values

39. 39 Thermal Noise with hypothesis of viscous Q (upper limit)

40. 40 Thermal Noise comparison with Virgo+ noise curve

41. 41 Thermal Noise comparison with Virgo+ noise curve and noise budget

42. Thermal Peaks study (from Marzia Talk) 42 The Lorentian fits results are in agreement with the expected thermal amplitudes and the measured Q’s values

43. 43 Theoretical prediction Measured curve The thermal model gives the correct prediction of the amplitudes of the peaks

44. 44 Theoretical prediction Measured curve The thermal model gives the correct prediction of the amplitudes of the peaks

45. 45 Theoretical prediction Measured curve The thermal model gives the correct prediction of the amplitudes of the peaks

46. A further check.... We subtract all known noise sources (the noise budget), without thermal noise, from the Virgo+MS sensitivity, and suppose that all remaining noise is of thermal origin. Virgo Sensitivity (September 13, 2011) Noise Budget – No Thermal Noise Curves cleaned from peaks using the standard Autoregressive Average Method (P.Astone) I.Nardecchia

47. Result of the subtraction: h 2 unknow noise = h 2 Virgo -h 2 noise budget (no thermal noise) Fit with Thermal Noise Model

48. To justify the unknown excess noise as of thermal origin, we should have: Q drum = (8  2 ) 10 3 ~ (1/5) Q drum WI  int = (3.4 ± 0.3) 10 -7 ~ (5)  int measured Averaged Q int = 1/  int < 3 10 6...but we have measured Q ~ 2.5 10 7

49. We have now a almost complete landscape of the present mechanical losses in the monolithic payloads. They are higher than expected. The lowest values are for the WI and NI drum modes. At least for the NI case, the Q measurement for the drum mode is influenced by mode coupling, that has no effect out of resonance However, even allowing for the worst case possible (i.e. the low Q’s are due only to viscous losses), the thermal noise model cannot account completely for the excess noise we see. The thermal noise model gives correct values for the peaks of the mirror modes. 49 Remarks

50. * Suspensions * From violins  * Why? Clamps? Marionette? * Measurements on the violins on the monolithic payloads planned * From pendulum  values dominated by recoil of RM which does not affect the thermal noise at (10,100 Hz) * Mirrors: * From higher Q  structural losses * From lower Q  upper limit on thermal noise there are viscous effects * Why low Q: Wire standoffs? * Measurements on the mirror Q planned 50

51. At High Frequency (Bulk Modes). We are studying tests to be made on the monolithic payloads now in operation (once the ITF is turned off) both acting inside the towers and in test vacuum chambers being prepared in Rome and Cascina. At Low Frequency (Pendulum Modes). A first order clamp optimization can be performed observing the Q values of violin modes, which are due to the same loss effects as the pendulum modes. We should foresee also a final check on an improved test facility (e.g. upgrading the facility in Perugia, or building a new one at EGO) Test and validation procedure during payload assembly. We are designing a vacuum chamber to be integrated in the clean room payload assembly facility at the 1500 W Hall at EGO. Monolithic NI and WI Payloads being measured in Rome We must improve the technology: