Noise issues in vibration sensing and isolation for Advanced

Virgo Eric Hennes

E.Hennes@Nikhef.nl

GWADW, Hawaii 2012, May 15

Advanced Virgo

Nikhef 2011-2014 “vibration” activities on AdV

144 m

3 km

EIB

angular alignment port

Laser

detection and alignment ports

3 km

z

dihedron

IMC

2GWADW May 15, 2012

• External Injection Bench Seismic Attenuation (SAS) • Isolation of 5 new suspended benches for linear alignment

• High sensitivity diagnostic accelerometer• Input Mode Cleaner:

- new End mirror + suspension

- new Dihedron + support

External Injection Bench (EIB) Seismic Attenuation (SAS)

Motivation (since 2009): • beam jitter noise is spoiling sensitivity • Ascribed to mechanical modes of

- bench frame (15-20, 30-60 Hz) - optical mounts (200-300 Hz)

• excited by both seism and “a bit of” sound• to be minimized for Virgo+ and AdV

Projection of vertical beam jitter on hrec Projection of EIB displacement on hrec

hrec (VSR2)

EIB displ projection on hrec

Coherent part

Virgo+

AdV

hrec (VSR2)

Jitter HOR projection on hrec

Coherent part

Virgo+

Jitter HOR projection on hrec

3

Old bench support

GWADW May 15, 2012

Fiori et al.Fiori et al.

EIB-SAS Requirements

4

• Up to 40 dB attenuation > 10 Hz• Long term stability (RMS 20 m, 15 rad, max 1 oC variations• DC-control

GWADW May 15, 2012

Re

sid

ual

dip

lace

men

t [m

/√H

z]

EIB-SAS Solution option history

Chosen solution:Highly-compliant suspension

5GWADW May 15, 2012

Stiffer legs

Stiffer support

Active isolation (TMC-Stacis)

GWADW May 15, 2012 6

6-DOF passive attenuation, anti-spring technology• 3 GAS filters, 3 Inverted Pendulum legs

Active positioning and low-f resonance damping• 6 x LVDTs, 6 x geophones, 6 x voice coil actuator

• 800 kHz 18 bit ADCs

• 7 stepper motors

Optical bench

Built and tested at Nikhef, 2011

EIB-SAS: adopted from HAMSAS project (Caltech) & AEI-Hannover (2010)

EIB-SAS complication: horizontal GAS modes < 20 Hz

GWADW May 15, 2012

7/20

Yaw + z (12 Hz)

• Modes due to lateral GAS spring compliance• Can be damped by extending control bandwidth

x + (bench) roll (18 Hz)

z + yaw +(bench) pitch (16 Hz)

7

Damped

Ty

[rad

/√H

z]

7

xy

z

EIB-SAS complication: spring box modes 30–60 Hz

GWADW May 15, 2012 8

Springbox vertical bouncing mode ~ 50Hz

• Modes due to upper IP flex and spring box internal compliances• Can partially be damped with eddy current damped resonators

50 Hz

coupled tilt modes (~ 30-40 Hz)

10 cm

EIB-SAS: First major Advanced Virgo installation (Dec 2011)

GWADW May 15, 2012 9

EIB in acoustic enclosure

EIB-SAS after installation

EIB-SAS commisioning: beam jitter

GWADW May 15, 2012 10

The good news:Beam jitter significantly reduced < 100 Hz

But:Optics mounts keep resonating (200-300 Hz)

Fiori et al.

And …

EIB-SAS commisioning: bench motion and acoustic noise

GWADW May 15, 2012 11

Conclusions after many tests

•1 – 100 Hz: bench moved by acoustic noise from central building Airco

•40 - 50 Hz: second noise source is present

•Limited shielding by acoustic enclosure

•Optical mounts are moved by sound

Bench displacement

Sound level in acoustic enclosure

Fiori et al.

EIB-SAS: conclusions

GWADW May 15, 2012 12

• Commissioning EIB-SAS revealed prominent roll of acoustic noise

• Laser lab walls are cleanroom walls → do not shield acoustic noise

• EIB-SAS is doing only most of the job, but ….

• It is usefeul for Advanced Virgo ..

- to replace these walls by concrete walls

- to move Airco’s outside main building

MultiSAS: Isolating suspended benches

for linear alignment

GWADW May 15, 2012 13

5 similar systems consisting of: • MultiSAS (Nikhef)• Optical bench (DET/LAPP)• UHV vacuum mini-tower (LAPP)

3 km

3 km

z

MultiSAS: multi-stage 6DOF bench isolation & control

GWADW May 15, 2012 14

Schedule•Design approved•Prototype assembled•In-air testing started with dummy bench•Integration test at Nikhef/LAPP from Sep 2012•AdV production and first chamber installation 2013

Characteristics two-stage vertical isolation (GAS) 3-stage horizontal isolation (IP, P, P) 320 kg single-wire suspended bench sensing/control technology like EIB-SAS

Requirements @ 10 Hz (VIR-0128A-12)

h 2 E-12 m/√Hz

3 E-15 rad/√Hz

hRMS 2 E-5mm

RMS 3E-9 rad

tough!

MultiSAS: special GAS mechanics

GWADW May 15, 2012 15

Bottom GAS filter GAS blades below Filter body

Top GAS filter Down-tunable to

100 mHz thanks to combination of

over-compression and hysteresis

SiC magic wandsTransfer function down to ~ 10-

5 at 30 Hz thanks to excellent percussion effect compensation

TF MultiSAS intermediate filter with Magic Wands

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

0.1 1 10 100f (Hz)

yL/y

0

Transfer bottom filter with Magic wand

MultiSAS: IP equal bottom & top flexures (to be tested)

GWADW May 15, 2012 16

• Both flexures in compression• Allows for significant raise oftop plate bouncingand rigid leg modes

thin + thick flex equal flexes

material alu steel alu steelwall thickness 1 2 1 2thickness 7.4 6.7length 40top plate y 64 80 83 133rigid leg x/z 145 100 270 295

MultiSAS IP modes (FEM)

mmlower flex

8.760

modes Hz

thin (2mm) thick

leg

upper flex

MultiSAS Modal analysis: modes < 250 mHz

GWADW May 15, 2012 17

Top stage yaw (230 mHz)

Common yaw(10 mHz)

Common lateral(80 mHz)

…. and 3 more

MultiSAS: Modal analysis: modes < 2 Hz

GWADW May 15, 2012 18

Pendulum mode (1.7 Hz)

GAS mode (0.5 Hz)

Filter tilt (0.43 Hz)- coupling to horizontal

…. and 4 more

MultiSAS: Modal analysis > 60 Hz

GWADW May 15, 2012 19

Keystone rotation (250 Hz)

Keystone coupled mode (70 Hz)

…. Etc etc

Blade mode (340 Hz)

Multi-SAS horizontal residual displacement @ Virgo (FEM)

1.E-24

1.E-22

1.E-20

1.E-18

1.E-16

1.E-14

1.E-12

1.E-10

1.E-08

1.E-06

1.E-04

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03f (hz)

from horizontal ground motionfrom vertical ground motion (if 0.1% coupling)total

MultiSAS: residual horizontal displacement

GWADW May 15, 2012 20

keysto

ne & to

p stage

reso

nances

< 2 10-12 m/√Hz required

Margin 105 !

10-4

10-6

10-8

10-10

10-12

10-14

10-16

10-18

10-20

10-22

10-24

Res

idua

l dip

lace

men

t [m

/√H

z]

Frequency [Hz]

Calculated from FEM transfer functions (open loop)

Multi-SAS bench residual tilt @ Virgo (FEM)

1.E-24

1.E-22

1.E-20

1.E-18

1.E-16

1.E-14

1.E-12

1.E-10

1.E-08

1.E-06

1.E-04

0.01 0.1 1 10 100 1000

MultiSAS: residual tilt (FEM)

GWADW May 15, 2012 21

< 3 10-15 rad/√Hz required

Margin 3*103

!

10-4

10-6

10-8

10-10

10-12

10-14

10-16

10-18

10-20

10-22

10-24

Res

idua

l tilt

ang

le [r

ad/√

Hz]

Frequency [Hz]

MultiSAS: current state of prototype

GWADW May 15, 2012 22

• Cabling, Electronics and DAQ to be installed• Mechanics to be fine-tuned• Performance to be measured• Dummy bench in production• Looking forward to MiniTower for tests in vacuo• Development of diagnostic interferometric

accelerometer

GWADW May 15, 2012 23

High-sensitivity diagnostic accelerometer

Mechanics: monolithic single-axis Watt-linkage oscillator (Bertolini, 2005*)Projection of thermal noise xth reduced by choosing– low resonance frequency (~ 0.5 Hz)- large quality factor (> 100)- large mass (~ 1 kg)

Readout: based on balanced Michelson interferometer (Gray et al, 1998**)- LED source allows for low Relative Intensity noise (RIN)- Sensing of both reflected and transmitted beam >40 dB RIN

cancelling- fringe locking by feed back loop to piezo actuator or voice coil

On behalf of David Rabeling

**Optics & Quantum Electronics 31, 1999, 571-582*Nuclear Instruments and Methods in Physics Research A 556, 2006, 616–623

x

z

LED

1

2

PT

PR

Inverted pendulum

pendulumM P

M IPL

to PZT or Voice coil

GWADW May 15, 2012 24

Accelerometer mechanics

Transfer function:

0:resonance angular frequencyQ : Quality factor >>1A : percussion factor <<1K : total elastic stiffnessM : total mass (M P+MIP) kB : Boltzmann’s constant : loss angle in flexes

Projected thermal noise PSD:

Construction• Wire-cut monolithic aluminum• Symmetric pendulum + inverted

pendulum• All flexes (4x5x0.1 mm) in tension• Adjustable mass distribution (tuning)• Optional: voice coil actuator

k

MMgLQ IPP

)(1

1

For structural damping:

L=7 cm

Voice coil actuator

frame displacement

Mass-to-frame displacement

25

Interferometric read-outPhotodiode incident power

z : mass-to-frame displacementPinc: incident LED power: carrier wavelengthC : complex temporal coherence

LED

1

2

PT

PRPinc

zczC

PP

zczC

PP

inc

R

inc

T

4cos))/(Re(1

8

4cos))/(Re(1

4

z

Coherence length cRelated to source bandwidth

GWADW May 15, 2012 5 -4 -3 -2 -1 0 1 2 3 4 5

Relative PD intensity pattern (T and R)

c/2

zm

Readout current sensitivityLock on half fringe:

DCTincOut

IP

dz

dI,

4

To PZT or Voice coil

IOut

GWADW May 15, 2012 26GWADW May 15, 2012 26

Optical and electronic readout current noiseShot noise (SN) current

)(22

RTSNPPqi

Intensity noise

ADC noise 2

ADCi

Electronic noise

2

OpAmpi

2

,termalRi

< -40 dB of shot noise (?)Dark current noise

BW

Ii dark

dark

2

2

4log/)log(o

os

f

fm

n : number of bitsfs : sampling frequencyfos: over-sampling frequencyrf : transimpedance resistanceVop, Iop: OpAmp noise levelscv, cv,cv,: corner frequenciesVpp,: ADC peak-peak voltage

26

1

fsrf

GWADW May 15, 2012 27

Projections of noise on frame displacement

3 fm /rt(Hz)

MultiSAS Requirement @ 10 Hz

measurable bench motion

Femtometer noise

For accelerometer with f0 = 0.5Hz, Q =100

Bench residual

Input mode cleaner (IMC) modifications: Dihedron support

28

• modes 55, 78, 82 Hz disappeared

• new support: 240 Hz (Hertz contact)

SSFS corr signal

Old leg support

New stiff support

replaced Oct 2011

GWADW May 15, 2012

Genin et al.

144 m

EIB

ITF

IMC modifications; 2. New Dihedron

GWADW May 15, 2012 29

• Shaped and polished by Optronica (Den Helder, NL)

• Mirrors connected by Van der Waals bonds (no adhesive)

• Angle (89o 58’ 58’’) machined to 0.4’’ accuracy (max 2” allowed)

• To be coated (by IPN-Lyon)

• To be installed in 2013

IMC modifications: New End Mirror suspension

30

• mirror twice as thick• including front (and back?) baffle • adapting Marionette and gear box• new installation procedure /tools• largest challenge: connect baffles stiffly to reference mass

GWADW May 15, 2012

144 m

EIB ITF

GWADW May 15, 2012 31

Summary

• EIB meets requirements, provided acoustic sources be removed or better shielded.

• MultiSAS prototype is working so far; performance to be fully tested

• New IMC dihedron mirror waiting for coating, than ready to be installed on its new support

IMC end mirror suspension: a challenge regarding stiff baffle mounting

• Diagnostic accelerometer R&D looks useful tool for bench seismic attenuation performance testing

The tracking interferometer can measure RMS test bench motions up to 2.8 m. Larger excursions can be compensated using the voice coil actuator.

Projections of noise and bench residual on sensor displacement z

System design parameters

Component list