Download L.Barsotti: Virgo commissioning progress

Virgo Commissioning
Status
WG1 meeting
Potsdam, 21st July 2006
1
Full ITF re-lock
 Mid of March: 7 Watts entering the ITF
Recycling Cavity Power (1 day)
Recycling gain = 25
(instead of 45)
 Locks not longer than a few minutes
 Recycling gain lower than expected
2
Other problems observed
 Clipping of the beam discovered at the level of the
output telscope
Suspended detection bench
3
Other problems observed
 Clipping of the beam discovered at the level of the
output telscope
 Matching of the beam with the cavities only 88%
 Reflected beam shape very bad
ITF locked
4
Tring to fix problems
 Centering of the beam on the mirrors
 Improvement of the matching
 Matching improved (88%96%)
 Clipping disappeared
5
Interferometer powers
1 month
 Recycling gain from 25 to 40
 280 W on the BS
 10 times more power than C7 (25 W)
6
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
7
Locks long enough to see
thermal effects
see Julien’s talk
Sideband power
8
Locks long enough to see
thermal effects
 dramatic change of the locking parameters
in the firts minutes of lock acquisition
 quite challenging to keep the ITF locked
9
Coupling with alignment fluctuations
0.4 mrad
10
Coupling with alignment fluctuations
 locking parameters very sensitive to
alignment fluctuations
(Locking/Alignment shifts)
 small window in which the locking
parameters make the ITF more stable
11
Useful tools
 On-line monitor:
 ugf of the longitudinal loops
 P\Q of the error signals
 Automatic gain adjustment
(Differential ARM loop)
12
Useful tools
 Scanning Fabry-Perot on the dark fringe beam
 Sidebands always unbalanced, instabilities clearly
correlated with one sideband vanishing
13
Improvements
 Easier to identify possible sources of instabilities
 Help in tuning locking parameters
14
Results
1- Lock acquisition reliable
W
15
Once the lock was stable enough..
… it was possible to close the automatic alignment:
 further improvement of the locking stability
 ITF conditions more repeatable
* new alignment procedure tested and implemented
 relaxed constraints on the locking parameters
16
Results
2- Typical locking periods of hours
Automatic alignment ON:
10 loops closed
17
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
18
Presented by Romain
at the last
collaboration meeting
Noise Budget
Sensitivity
BS length control noise
PR length control noise (direct coupling)
Arm mirror actuator noise
BS actuator noise
B1 shot noise
Sensitivity
B1 electronic noise
Oscillator phase
noise
B5_ACp
(freq. servo error signal)
Laser frequency noise ?
Yes!
19
19
PRCL sensing noise reduction
 Increasing of the light impinging the photodiode (just done)
Current sensitivity
B2_3f readout noise (4 mW)
B2_3f readout noise with 100 mW
Expectations, no direct
measurement yet
Further noise
reduction by
switching on B2
20
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
21
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
22
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
23
Matching and beam centering
Parabolic
telescope

Beam centering (clipping
removal) and matching
imply to act on injection
bench telescopes
Spherical
telescope
Iterative
procedure:
Beam-mirror
centering
Astigmatism
removal
24
Centering techniques
methods:

Image analysis using camera local control (only for beam splitter)

Angle to length coupling
25
What has been intentionally changed?
26
Scan of the B2_3f demdoulation phase
(automatic alignment closed, thermal drift over)
27
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)
28
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 6
operations (actuators noise
reduction, acoustic enclosure,
feet detection lab)
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
29
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
30