1

Virgo Commissioning Status

WG1 meeting Potsdam, 21st July 2006

2

Full ITF re-lock

Locks not longer than a few minutes

Mid of March: 7 Watts entering the ITF

Recycling Cavity Power (1 day)

Recycling gain lower than expected

Recycling gain = 25

(instead of 45)

3

Other problems observed

Clipping of the beam discovered at the level of the output telscope

Suspended detection bench

4

Other problems observed

Reflected beam shape very bad

Matching of the beam with the cavities only 88%

Clipping of the beam discovered at the level of the output telscope

ITF locked

5

Tring to fix problems

Centering of the beam on the mirrors

Improvement of the matching

Clipping disappeared

Matching improved (88%96%)

6

Recycling gain from 25 to 40

1 month

Interferometer powers

280 W on the BS

10 times more power than C7 (25 W)

7

Re-lock of the ITF End of May

Lock still not stable

Oscillations around 30-50 Hz

Present “everywhere”

Not clearly connected with any longitudinal loop oscillation

Quite often they caused the unlock of the ITF

8

Locks long enough to see thermal effects

Sideband powersee Julien’s talk

9

dramatic change of the locking parameters in the firts minutes of lock acquisition

quite challenging to keep the ITF locked

Locks long enough to see thermal effects

10

Coupling with alignment fluctuations

0.4 rad

11

locking parameters very sensitive to alignment fluctuations (Locking/Alignment shifts)

small window in which the locking parameters make the ITF more stable

Coupling with alignment fluctuations

12

Useful tools On-line monitor: ugf of the longitudinal loops

P\Q of the error signals

Automatic gain adjustment (Differential ARM loop)

13

Useful tools

Scanning Fabry-Perot on the dark fringe beam

Sidebands always unbalanced, instabilities clearly correlated with one sideband vanishing

14

Easier to identify possible sources of instabilities

Help in tuning locking parameters

Improvements

15

Results

1- Lock acquisition reliable

W

16

Once the lock was stable enough..

further improvement of the locking stability

ITF conditions more repeatable * new alignment procedure tested and implemented

relaxed constraints on the locking parameters

… it was possible to close the automatic alignment:

17

Results

2- Typical locking periods of hours

Automatic alignment ON: 10 loops closed

18

Results

3- Start of low noise operations as in C7

Dark fringe controlled with B1 (OMC on resonance)

Re-allocation to the marionette + low noise coil drivers

More aggressive filters in the longitudinal loops

19

Sensitivity

BS length control noise

PR length control noise (direct coupling)

Arm mirror actuator noise

BS actuator noise

B1 shot noise

B1 electronic noise

Oscillator phase noise

Laser frequency noise ?

19

Presented by Romain at the last

collaboration meeting

Yes!

Noise Budget

Sensitivity

B5_ACp (freq. servo error signal)

20

PRCL sensing noise reduction

Further noise reduction by

switching on B2

Current sensitivity

B2_3f readout noise (4 mW)

B2_3f readout noise with 100 mW

Increasing of the light impinging the photodiode (just done)

Expectations, no direct measurement yet

21

Noise Reduction: near future

Length control noise: Improvement of MICH-PRCL longitudinal loop decoupling

Optimization of the automatic alignment loops (see Maddalena’s talk)

Frequency noise reduction

22

Noise Reduction: already planned actions

Vibration isolation of external detection bench DONE

Actuators noise: plans for new coil drivers

Acoustic noise: plans ready for installation of acoustic enclosure in the laser

Diffused light mitigation: optimization of the benches optical set-up started, need few iterations

23

Conclusions

It seems that we can survive to the thermal effects, but studies are in progress

Short term plans: complete automatic alignment, increase locking robustness (difficult to recover a stable lock after changes in the system, see last week)

Noise hunting just started

24

Matching and beam centering

Spherical telescope

Parabolic telescope

Iterative procedure:

Beam-mirror centering

Astigmatism removal

Beam centering (clipping removal) and matching imply to act on injection bench telescopes

25

Centering techniques

methods:

Image analysis using camera local control (only for beam splitter)

Angle to length coupling

26

What has been intentionally changed?

27

Scan of the B2_3f demdoulation phase(automatic alignment closed, thermal drift over)

28

Laser frequency noise ?

Dark fringe signal coherent with B5_ACp between 240 Hz and 6 kHz

B5_ACp = error signal of the laser frequency stabilization loop (SSFS)

Also coherent with the angular error signals of IMC automatic alignment

B5_ACp superimposed on Dark Fringe Signal using the 444 and 1111 Hz lines

See logbook entry 12603 by M. Evans

Sensitivity

B5_ACp

Conclusion : B1_ACp and B5_ACp see the same noise (presumably laser frequency noise)

29

Global view for 2006

Main task Duration (weeks) In parallel/remarks

Completion of recycled interferometer commissioning

8 High frequency noise hunting robustness increase locking loops

Noise hunting: already planned operations (actuators noise reduction, acoustic enclosure, feet detection lab)

6 High frequency noise huntung

Noise hunting: control noises “first reduction” (angular and longitudinal)

6 High and intermediated frequency noise hunting

Noise hunting: scattered light reduction

4 High and intermediated frequency noise hunting

Total: 6 months (end of 2006)

Start data taking during long week-end as soon as the interferometer is stable and sensitivity better than C7 (september?)

Priority to the high-intermediate frequency range

Goal: factor 10 in the inspiral range

30

Plans for 2007

Science data taking

Shutdown with upgrades to be defined:

Eddy current removal

Thermal compensation implementation

Acoustic mitigation 2nd generation?

Optical table re-shuffling and diffused light mitigation 2nd generation ?

Mode-cleaner mirror replacement ?

Re-commissioning

Noise hunting 2nd phase