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, Sep. 2013

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

3 3 kms (1.9 m) gravitational wave detector

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

5 Direct observation with Michelson interferometers Need to measure length changes of ΔL/L of

6 Direct observation with Michelson interferometers Need to measure length changes of ΔL/L of

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

8 Initial detector

9 SourceN low N re N high VirgoNS-NS BH-BH 2 x AdvancedNS-NS BH-BH Initial detector

Spanner in the works… 10

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

Beam jitter noise from external injection bench 12

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

Requirement on EIB motion 14

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

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

Solution? Passive isolation technology 17

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

Longer pendulum = better isolator 19 1/f 2

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

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

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

Vertical isolation: geometric anti-spring filter 23

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

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

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

EIB-SAS 27 M. Kraan

EIB-SAS 28 M. Kraan

EIB-SAS 29 M. Kraan

EIB-SAS 30 M. Kraan

EIB-SAS 31 M. Kraan

EIB-SAS 32 M. Kraan

 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

Inverted pendulum & GAS filter modes 34

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

Actively damp low frequency resonances with blended sensor 36

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

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

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

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

Isolation performance 41

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

Transfer function EIB-SAS 43 Piezo shaker system

Transfer function EIB-SAS 44 Piezo shaker system

Vertical transfer function EIB-SAS < 100 Hz 45

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

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

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

Vertical TF EIB-SAS > 100 Hz 49

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

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

Damping the 182 Hz resonance 52

Damping the 182 Hz resonance 53

Horizontal transfer function 54

Horizontal transfer function: 16 Hz mode 55

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

Horizontal transfer function: 37 Hz mode 57

Horizontal transfer function: 37 Hz mode 58

Damping 37 Hz mode 59

Damping 37 Hz mode 60 Frequency [Hz]

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

Does EIB-SAS meet the requirement? 62

Displacement spectrum of Virgo 63

EIB-SAS displacement Virgo 64

 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 Summary 65

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Extra slides 67

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

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

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

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

Improved measurement of vertical TF 72

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

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

Interferometer (3 km) Vacuum system Injection system

Transfer function of inverted pendulum κ

Frequency (Hz) Transfer function κ

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

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