1

Virgo commissioning progress

Post VSR1 plans

E. Tournefier

STAC meeting June 26th ,2007

2carrierSidebands

15 minutes

Status at last STAC

• Thermal effects => fine tuning of parameters during lock acquisition + slow lock acquisition

• ITF stably locked (Weekend Science Runs) but• Controls needed to be improved (longitudinal, angular, suspension):

=> stability, noise re-introduction, stationarity, duty cycle• Control noises had to be reduced and environmental noises to be understood

WSR5 (Nov 2006)

3

Status now• Thermal effects still with us (waiting for thermal compensation)

=> still need fine tuning of parameters during lock acquisition + slow lock acquisition

• ITF control well improved: – reliable and more stable controls (long locks), good stationarity, – control noise subtraction (no impact above 40 Hz), – duty cycle improved against environmental conditions

• Noise well reduced (both controls and environmental)but…• Still noises to understand

4

Next steps – Diffused light

Install as soon as possible acoustic isolation

Detection lab

End benches

Perform diffused light mitigation

Detection lab

End benches

Understand better a solution for the Brewster noise

Replacement with a bigger one

Remove it ?

Understand possible clipping/spurious beam in vacuum

Modeling of all the beams

Mitigation – conservative approach

OK

OK

DoneShall we?

OK (to be continued)

Last STAC

5

Next steps – Control noise

Frequency noise improvements

Install Better SSFS (common mode servo ) electronics (under design)

Understand sensing noise (diffused light?)

Longitudinal control noise reduction

More aggressive filtering

Alpha technique frequency dependent

Understand sensing noise (diffused light?) and couplings in the auxiliary d.o.f. error signal (thermal lensing?)

Angular degrees of freedom

Mirror/beam centering – coils balancing ongoing

More aggressive filtering on going

OK

OK

started

OK

OK (improved error signal)

Last STAC

6

Next steps – Control improvements

Increase gain of the automatic alignment loops

Improve suspension control

Global inverted pendulum control

Vertical inertial damping

OK

OK (and more)

Last STAC

7

Activities since last STAC

• December 2006 – April 2007: 5 more WSRs– Improvements of controls (longitudinal, angular, suspensions)– Environmental noise (diffused light, magnetic) investigations and reduction

• April 6th – 18th electrical shutdown:Infrastructure works:– Electrical works, Computing (UPS, civil work, re-organisation,..)Detector improvements- Acoustic enclosure around external detection bench- Replacement of Brewster window with a larger oneRestart went ok: ITF relocked within ~2days

• April 18th –May 18th :– Acoustic enclosures at end benches– Scattered light investigations (Brewster) + other environmental noises– Improvements of controls (longitudinal, angular, suspensions)– Change of naming convention (V1:channel_name)for easier data exchange with

LSC

• May 18th: start VSR1– Continue noise investigations + small control improvements

8

Interferometer controls

• Thermal side-effects

• Longitudinal and angular controls

• Mirror suspension control

9

Lock acquisition: thermal transient

• Fine tuning needed for lock acquisition: – demodulation phases, engagement of loops, gains, offsets on error signals,

…Plus:• Variations in the thermal transient:

seem related to activities in laser lab but not understood

Some lengthy relocks

10

Thermal effects on sidebands: first studies

• Image of the sidebands (first step of phase camera):scanning system on B5 beam: - the beam is scanned on a pin-hole + photodiode - demodulated signal is used to reconstruct the sidebands shape

Clear defocusing effect

Need thermal compensation system + complete phase camera (see Michele’s talk)

11

Mirror longitudinal controls: noise reductionPRCL control noise => sensed by B5 => MICH control noise => sensed by dark

fringe (B1)1/ Built a signal as stable AND less noisy than B2_3f (mixing B2 and B2_3f) 2/ online noise subtraction:

- include frequency dependence (f) - add a servo to tune the time dependance of the global gain

PRCL

MICH

B2_ACpmix

(f)

(f) => MICH noise impact reduced by ~ 50

- with =0 - with measured (f)

12

Frequency stabilization and frequency noise

• New electronics designed and installed: – Better layout– Improved filter => frequency noise reduced at high

frequencies+ new functionality (switch between input signals)

• Alignment stability improved coupling of frequency noise also well reduced

13

Mirror actuator noise

BS actuator noise reduced in May

The arm mirrors actuators need to be improved: to be done during VSR1 (will we find the Eddy currents noise?)

Next: new coil drivers + new DACs (see Michele’s talk)

DAC

DSPCoilDriverG

Emphasis DeEmphasis DeEmphasis

14

Longitudinal control noises: summary

WSR5 (Nov 2006)

VSR1 (now)MICH noise

PRCL noise

frequency noise

15

Mirror angular controls

• Control loops improved:– Add a second modulation (8 MHz) to control the common end motion– Optimized filters with more gain => robustness and stability

• Global control upgrade: more flexibility, noise injection,…

Alignment signals

DF and recycled powers

8MHz

-> Drift control (10mHz)

-> Drift control

16

Angular control noise

• Beam centering on the mirrors:– Now within ~ 1mm => reduced coupling– Now automated

• More aggressive filters less noise reintroduction

Angular noise budget

The angular noise is not limiting the current Virgo sensitivity

This noise can be further reduced:- More power on B1p quadrant- Electronic noise reduction: new

electronics (see Michele’s talk)

Should be compliant with Virgo design above 20-30 Hz

B7

B8_q2

B8

WE

WINI NE

BS

17

Suspension control: bottom stage

Compensation of non-linear z -> coupling:Large seismic activity large correction sent to the marionette (zM) y recoil of F7 (and payload) Side effects on alignment

Solution: compensate for z -> y coupling

Need a quadratic compensation:

Dark fringe: alignment and total power

- No compensation- With compensation

y=a*zM +b*zM2 (payload: b=a/25)

Correction signals

zM

ycorr

y

Under similar seismic activity:

18

Suspension control: top stageOld problem: environmental noise reintroduced by Lvdt (seism) and Acc (wind) used for top stage control

Several strategies developed:1/ Panoply of error-signal blending depending on environmental conditions (‘onfly tuning’)2/ Use the ITF longitudinal error signal instead (Global Inverted Pendulum Control)=> z correction to the mirror well reduced

GC (reconstructed z)

LVDT

LVDTLVDTLVDT

VSR1: enabled only for NE-WE

No GIPCWith GIPC

old new

Other improvements: • Vertical damping on long suspensions• Local controls: optimized filters

19

Sensitivity versus wind and sea activity

Illustration of the improvements of angular control and suspension control

Empirical formula: Horizon = H0(1 - a x seism – b x wind)

WSR1 (Sept 2006): a= 0.37, b= 0.37 VSR1 (May-Jun 2007):a= 0.07, b= 0.04

Sensitivity to bad weather conditions is well reduced The lock can be kept in bad weather conditions

- Measured horizon- Sea activity- Wind activity- Predicted horizon

20

Environmental noises

• magnetic noise

• scattered light- optical benches- Brewster windows

21

Magnetic noise

• Before WSR10 magnetic noise was limiting the sensitivity between 50 and 110 Hz

• Investigations: track the sources of magnetic field close to the input mirrors (more sensitive due to wrong polarity of the magnets)=> found noisy power supplies=> power supplies displaced

Home made portable magnetometer

Dark fringe

• Still some evidence for magnetic noise: under investigation

22

Scattered light

Environmental noise acting on in air components +Scattered light from in air components =-------------------------------------------------------------Phase noise in the interferometer (with the typical environmental-like noise structures)

Laser

Brewsterwindows

End benches

External bench

Injection bench

Detectionsuspended bench

Actions:- reduce diffused light on benches- acoustic isolations- large Brewster windows

23

Scattered light at end benches

Evidence for diffused light by the optics of the end benches (Jan 2007)Actions: 1/ use more rigid mounts for critical optics and dump secondary beams (Feb 2007)

WSR7WSR9: after 1/

Acoustic injections => acoustic noise still very close to the sensitivity floor

2/ install acoustic enclosures

Tentative acoustic noise projection

24

Acoustic enclosures

• External detection bench:– Displace bench from the tower (~50cm)– Install acoustic panels (a room into the room)

• End benches:– Simpler: build a room around the benches

DetectionEnd buildings

25

Scattered light and acoustic isolation

Tentative acoustic noise projection with acoustic enclosureSeismic noise on the optical bench

- No acoustic enclosure- With acoustic enclosure

After acoustic enclosure installation:

Impact of acoustic noise wellreduced above 100 Hz

Tentative acoustic noise projection before

26

Brewster window + detection tower

Brewster link

Detection tower

Tentative projection of ‘Brewster noise’

Observations:- Brewster+detection tower = area very sensitive to acoustic noise- Tentative noise projections: Brewster could be a limiting factor

But: very difficult to make the difference between the Brewster and the detection tower

Damp all spurious beams inside the detection tower

Replace Brewster with a larger one (to fulfill: diameter > 5 x beam waist)

27

Detection tower scattered light

Dump the secondary beams with black glass baffles:- Reflection by output port windows- Secondary beams (from second face of optics) on the suspended bench

B1sB1

B1p

B5

L3 /2OMC

M1

M5

L7

28

New Brewster windowApril shutdown:

Detection Brewster replaced with a larger one: 16cm -> 19.6 cm

Result: the noise is increased…After testing several hypothesis,found the culprit: aluminium baffle

=> Protect it from light the retro-diffused by the detection bench

Detection

29

New Brewster window ‘patched’

• After protecting the aluminium baffle: recovered the pre-shutdown sensitivity

• Additionnal small improvements: - ‘damp’ the Brewster link (weight+rubber)- smaller vacuum pump on SR tower improve sensitivity from 100 to 200Hz

The path of the noise in this area still has to be understood

Old BrewsterNew Brewster‘improved’ New Brewster

30

Sensitivity and noise budget

31

Sensitivity measurement: actuators calibration

Found a frequency dependence of the actuators response (could be due to Eddy current effects)

“Improves” sensitivity by 20% at high frequencies

10%

32

VSR1 noise budget

Magnetic noise: under investigation

Not yet understood:hints for jitter/Pnoise from the injectionsystem

Environmental noise(laser lab)

Actuator noise=> shaping filters to

be installed

Laser powerOMC matching

33

Environmental noises: some hints

• Below 30 Hz: beam jitter due to acoustic noise on laser bench ? some improvements obtained with better air conditioning flux

• Structures from 200 to 800Hz: input beam jitter, power noise?

Investigations ongoing during the run

Input beam jitter Acoustic noise on laser bench

Beam jitter vs acoustic noiseBeam jitter vs dark fringe

dark fringedark fringe IMC reflection

34

Detector operation –

Few words on VSR1

35

Detector monitoring/automation

• Detector monitoring, automation: the essential every day’s life tools, regularly upgraded

• Logbook: regular additions depending on user needs (more with the run!)

36

VSR1 : some statistics

• Good stability, long locks ( up to 59 hours)• Gaussianity of the data is good, low trigger rate, low SNR• NS-NS horizon (averaged) ~ 3.5 Mpc• Science mode duty cycle ~ 85%• Unlocks:

– Technical: IMC fast unlock, Gc crash– Earthquakes, (bad weather)– Maintenance, commissioning breaks

Horizon NS-NS (averaged value)

1 month

37

Commissioning activities during VSR1

Alignment drifts observed during long locks: related to the mis-centering of one end quadrant (used for BS control)

=> spoils error signal (AC) Improvement: include quadrant asymmetry in the error signal for BS control

Small drifts still there Try to use another error signal (B1p?)Longer term: Install galvanometer to keep centering

in science mode Reshuffle the end benches to have cleaner signals

realignment

Dark fringe

Q81 asymmetry IMC fast unlocks

- adjustement of IMC gain loop - repair electronics (loose connections)

=> rate smaller

Suspension controls: some improvements /test of configurations / try to keep lock during earthquakes

Environmental noise investigations: magnetic, acoustic, seismic

38

Long term observations: Etalon effect!• Etalon effect:

small FP cavity inside input mirrors (due to AR face) effective reflectivity modulated with mirror thickness (temperature) … and so the finesse

AR HR HR

r1 r2 r3LA

LB

AR HR HR

r1 r2 r3LA

LB

B7/B8 phd

-FP transmitted power-Input mirror temperature

Temperature variation

FP

Tra

nsm

itte

d po

wer

No clear effect on sensitivity now… but to take into account for Virgo+

F/F = ± 3.5%

39

Post VSR1 plans

• Noises: Environmental noise investigations are going on during VSR1,simple actions will be done during the run– Magnetic noise close to the mirrors: identify sources and ‘remove’ them – Acoustic, seismic noise in the laser lab:

find noise sources, reduce coupling to ITF– Acoustic noise at detection port:

understand the path => remove Brewster?- Reduce the mirror actuator noise: shaping filters (to be done during VSR1)- Angular noise reduction (not urgent)

• Controls:– Rearrange the end benches: better error signals from quadrants– Install better centering system for quadrants (‘science mode’ compatible)– Improve the control of the short suspensions (now the limiting ones)– Revise the longitudinal control using the 8MHz modulation? (cleaner signals)

• Thermal effects: (see Michele’s talk)– Clean the input mirrors ? (if not too risky) – Install and commission the thermal compensation system when ready (Jan

2008?)+ phase camera

40

41

Conclusion

• A lot of progress on the interferometer controls (still suffering from thermal effects): – Stability, robustness, duty cycle ok for science data taking– Noise re-introduction only a limitation below 40 Hz– Control scheme can still be improved:

• Quadrants / use 8MHz for longitudinal / short suspensions

• Good progress on the environmental noise:– Magnetic noise: well reduced still under investigation– Scattered light:

• Benches: improvement of benches setup + acoustic enclosures End benches and detection bench are safe now

• Brewster: larger one installed + investigations on noise path To be better understood (remove Brewster?)

– Remaining environmental noise under investigation (ISYS) Actions to be defined when we have clearer ideas

42

Backup slides

43

Discussion

• ITF noise larger because of new Brewster• Brewster link vibrating more than before? No.• Sensitivity to Brewster vibrations larger than before? Yes• Why?• What is the mechanisms ?

BEAMSPLITTER DETECTION

1) Scattering of spurious light coming from the ITF

2) Scattering of spurious lightgenerated in the Brewster

3) Scattering of spurious light coming from the detection

44

• With new larger Brewster new light visible on the detection bench- Light visible at ~10 cm from the axis of the main beam- This light is missing the first detection lens (L1, diameter 12 cm)- This light is diffused on a couple of supports on the detection bench

New observations (III)

B1s

B1

B1p

B5

L3/2OMC

M1

M5

L7

45

• Julien Marque (2004)

Old prediction: spurious beams

Bd3

Bd4

Bi1

46

• Julien Marque (2004)

Old prediction: spurious beams

Bd3 and 4

47

• With the old brewster

One of the predicted spurious beams

Diaphragms Brewster

B1

B5

Brewster link axis

Distance from BS (m)

Dis

tanc

e fr

om w

est a

xis

(cm

)

One spurious beam

48

• With the new brewster

One of the predicted spurious beams

Diaphragms Brewster

B1

B5

Brewster link axis

Distance from BS (m)

Dis

tanc

e fr

om w

est a

xis

(cm

)

One spurious beam

49

• With the new brewster

• Considering beam diameter defined as 2 w0

One of the predicted spurious beams

Diaphragms Brewster

B1

B5

Brewster link axis

Distance from BS (m)

Dis

tanc

e fr

om w

est a

xis

(cm

)

One spurious beam

50

• Additional diaphragm before the Brewster

Added from SR tower

A possible mitigation

Diaphragms Brewster

B1

B5

Brewster link axis

Distance from BS (m)

Dis

tanc

e fr

om w

est a

xis

(cm

)

One spurious beam

51

Scattering of spurious light from the ITF ?

• Yes, but ….

• …… no difference in the ITF noise

52

Damping the Brewster

53

• Injection with shaker: comparison with old Brewster

Noise injections (May 9th)

54

• Injection with loudspeaker: comparison with old Brewster

Noise injections (May 9th)

55

• Tapping tests on injection Brewster, injection tower, injection table- Small effects on ITF sensitivity- No excitation of ITF noise structures/resonances- Much less sensitive than detection tower and Brewster

• Tapping tests on injection Brewster, injection tower, injection table- Very small effects on ITF sensitivity- No excitation of ITF noise structures/resonances

• Tapping test attempted on NI- failed due to unlock

• Need to study sensitivity to all towers vibration- need to learn how to excite towers without unlock- place seismometers in more useful positions (now measuring verticalseismic noise near tower base)

More investigations (IV)

56

“Mystery noise”

57

“Mystery noise”

58

“Mystery noise”

59

“Mystery noise”