1. New in-air seismic attenuation system for the next generation gravitational wave detector M.R. Blom, A. Bertolini, E. Hennes, A. Schimmel, H.J. Bulten, M.G. Beker, F. Mul, M. Doets, J.F.J. van den Brand 13 th TAUP Conference, Asilomar Conference Grounds, Pacific Grove, California, 8 - 13 Sep. 2013

2. Indirect evidence for gravitational waves 2 1974: Hulse & Taylor’s discovery of first binary pulsar Nobel prize 1993

3. 3 3 kms (1.9 m) gravitational wave detector

4. 4 Virgo, Cascina, Italy GEO600, Hannover, Germany LIGO, Hanford, WA KAGRA, Hida, Japan LIGO, Livingston, LA

5. 5 Direct observation with Michelson interferometers Need to measure length changes of ΔL/L of 10 -23

6. 6 Direct observation with Michelson interferometers Need to measure length changes of ΔL/L of 10 -23

7. Length changes due to gravitational waves - sensitivity 7 Strain = ΔL/L [1/√(Hz)] Frequency [Hz] we measure 0.0000000000000000003 m over 3km!

8. 8 Initial detector

9. 9 SourceN low N re N high VirgoNS-NS BH-BH 2 x 10 -4 0.02 0.007 0.2 0.5 AdvancedNS-NS BH-BH 0.4 40 20 400 1000 Initial detector

10. Spanner in the works… 10

11. 11 External Injection Bench LASER bench Vacuum system Interferometer (3 km)

12. Beam jitter noise from external injection bench 12

13. Beam jitter noise from external injection bench Modes of legs and optics mounts introduce beam jitter noise 13 Needs to be reduced for AdV

14. Requirement on EIB motion 14

15. Commercial “shock damper”: STACIS 15 Frequency (Hz) Acceleration (m/s2)

16. Commercial “shock damper”: STACIS 16 No commercial product available! Frequency (Hz) Acceleration (m/s2)

17. Solution? Passive isolation technology 17

18. A simple pendulum is a 2 nd order low pass filter 18 1/f 2

19. Longer pendulum = better isolator 19 1/f 2

20. Long pendulum is impractical 20 ω 0 = 0.1 Hz → L = 24.8 m 1/f 2

21. Use inverted pendulum 21 1 m Gravity acts as anti-spring:

22. Horizontal isolation: inverted pendulum 22 Gravity acts as anti-spring: ω 0 = 0.1 Hz → L = 1 m

23. Vertical isolation: geometric anti-spring filter 23

24. Vertical isolation: geometric anti-spring filter 24 Tension in blade springs acts as anti-spring

25. Vertical isolation: geometric anti-spring filter 25 Tension in blade springs acts as anti-spring

26. External Injection Bench Seismic Attenuation system: EIB-SAS 26 Adapted from the HAM-SAS system

27. EIB-SAS 27 M. Kraan

28. EIB-SAS 28 M. Kraan

29. EIB-SAS 29 M. Kraan

30. EIB-SAS 30 M. Kraan

31. EIB-SAS 31 M. Kraan

32. EIB-SAS 32 M. Kraan

33.  Comply with seismic attenuation request  Long-term stability and DC control o 1 week o x ref ± 20 µm o θ ref ± 5 µrad  Stable w.r.t. temperature variations of 1 º C  Characterize mechanical modes and acoustic coupling Requirements 33

34. Inverted pendulum & GAS filter modes 34

35. Actively damp the IP and GAS filter resonances Real-time digital control system  800 kHz 18 bit ADCs  6 displacement sensors (LVDTs)  9 inertial sensors (geophones)  6 voice coil actuator 35

36. Actively damp low frequency resonances with blended sensor 36

37. Sensor correction with geophones on the ground 37 x direction y direction (vertical) z direction

38. Closed loop, long term stability (1 week) RMS deviation of set point is within requirement (5 µrad for tilt d.o.f., 20 µm for translational d.o.f.) 38

39. Closed loop stability w.r.t. temperature changes (-1°C) 39 As expected, vertical d.o.f. (y) affected strongest: < 3 µm/K Loop gain = ~ 130

40. Closed loop stability w.r.t. temperature changes (+1°C) 40 As expected, vertical d.o.f. (y) affected strongest: < 3 µm/K EIB-SAS can compensate for ± 3 K

41. Isolation performance 41

42.  GAS filter tuned to 300 mHz  60 dB attenuation @ 10 Hz  Above 50 Hz resonances in setup 42 Transfer function GAS filter

43. Transfer function EIB-SAS 43 Piezo shaker system

44. Transfer function EIB-SAS 44 Piezo shaker system

45. Vertical transfer function EIB-SAS < 100 Hz 45

46. Vertical transfer function EIB-SAS 46 48 Hz Bounce mode of the springbox on the inverted pendulums

47. Eddy current damper for bounce mode @ 48 Hz 47 Springbox ~ 300 kg, damper 4 kg

48. Eddy current damper for bounce mode @ 48 Hz 48 Springbox ~ 300 kg, damper 4 kg

49. Vertical TF EIB-SAS > 100 Hz 49

50. Vertical TF EIB-SAS > 100 Hz 50 Springbox resonances Resonances of GAS filter blades

51. Vertical TF EIB-SAS > 100 Hz 51 Springbox resonances Resonances of GAS filter blades

52. Damping the 182 Hz resonance 52

53. Damping the 182 Hz resonance 53

54. Horizontal transfer function 54

55. Horizontal transfer function: 16 Hz mode 55

56. Horizontal transfer function: 16 Hz mode 56 Damped by control system

57. Horizontal transfer function: 37 Hz mode 57

58. Horizontal transfer function: 37 Hz mode 58

59. Damping 37 Hz mode 59

60. Damping 37 Hz mode 60 Frequency [Hz]

61. Horizontal transfer function: 88 Hz “mode” 61 Not a mode of EIB-SAS, but of excitation system

62. Does EIB-SAS meet the requirement? 62

63. Displacement spectrum of ground @ Virgo 63

64. EIB-SAS displacement projection @ Virgo 64

65.  New External Injection Bench Seismic Attenuation System for Advanced Virgo meets requirements  Measure EIB-SAS vertical TF with piezo shakers o Attenuate vertical ground motion with 40 dB o Horizontal with 60 dB  Installation in Advanced Virgo Nov. 2013 Summary 65

66. 66

67. Extra slides 67

68. SAS EIB LB SAS  MultiSAS features  Compact design o Inverted pendulums o Geometric antisprings o Consistent with 10 -15 m (rad)/√Hz (6 dof)  UHV compatible Latest activities: Multistage Seismic Attenuation System 68 multiSAS

69. Transfer function EIB-SAS: 1 st attempt 69 Excite the ground with a shaker bolted to the floor

70. Transfer function EIB-SAS: 1 st attempt 70 Excite the ground with a shaker bolted to the floor

71. Transfer function EIB-SAS: 1 st attempt 71 Acoustic coupling: Can we trust the TF measurement?

72. Improved measurement of vertical TF 72

73. Acoustic shielding will be improved for Advanced Virgo Commissioning EIB-SAS has shown the prominent role of acoustic noise above 100 Hz The walls between the central hall and the laser lab ( ▬ ) are cleanroom walls → they do not shield from acoustic noise 73 For AdV laser lab walls will be replaced by concrete walls

74. Interferometer (3 km) Vacuum system Injection system Output gravitational wave signal

75. Interferometer (3 km) Vacuum system Injection system

76. Transfer function of inverted pendulum κ

77. Frequency (Hz) Transfer function κ

78. Working on the bench: kinematic locking system Works on compressed air

79. Reproducibility of locked position 79  Locked position is reproducible within 50 µm/µrad  Floating position within 10 µm/µrad