1. VIRGO commissioning progress
22/03/2017
VIRGO commissioning progress
Paolo La Penna
for the VIRGO collaboration
European Gravitational Observatory

2. Status in December 2005
Virgo shutdown had started after C7 (19 September 2005)
The new IB had been installed in the IB tower (end November 2005
The fake dihedron was still mounted on the bench
The Nd:YAG beam (up to 5 W for the moment) had been sent into the bench: some light (with even some interference) was visible at the end of the MC
The optics on the bench were being realigned using the IB actuators: this operation was performed staying inside the tower, with the laminar flux on and the LC closed
The alignment of the IMC was going on (

3. The IMC was fully aligned in vacuum at about mid December.
Since then:
The IMC was fully aligned in vacuum at about mid December.
IMC locked at end of 2005.
Beam at the end of the ITF at begin of January 2006.
ITF alignment at mid of January.
First ITF cavities lockings at end of January.
Full RFC alignment at end of February.
Full locking of the ITF going on now (mid of March).
The full restart of the ITF, after IB installation,
took about three months

4. I – Injection system restart

5. Operation performed on the Injection System
Alignment and locking of the IMC in vacuum
Alignment of the IB optics in vacuum
Alignment of the beam on the ITF and telescopes tuning
Alignment and locking of the RFC
Setup and alignment of the EIB
BMS
IMC matching improvement
IMC automatic alignment
Power stabilization
RFC automatic alignment

6. Changes in Virgo after September shutdown
PR mirror
IB+RFC
EIB

7. Injection system
Lower stage
Upper stage

8. Difference old-new IB
Old IB
New IB

9. IMC alignment: december 2005
HeNe autocollimation on the MC mirror
Acting on the IB alignment
(checked with a ccd)

10. IMC alignment: december 2005
laser
YAG beam direct beam centering
on the MC mirror acting on the
external steering mirrors

11. IMC alignment: december 2005
laser
MC mirror alignment
until IMC resonances are visible

12. laser Pout  8 W IMC locking: december 2005 IMC locking
Feedback on laser pzt
using the reflection as a trigger

13. ITF alignment: 13 january 2006

14. RFC alignment and locking: february 2006
The Reference Cavity alignment has taken more time than expected
A first attempt to align it using the 20 W beam failed
A second attempt after having aligned a probe beam coming from the opposite direction, and looking at the RFC transmission, led to a poor RFC alignment (but it allowed to lock and start working on the ITF)
A third attempt overlapping the probe beam and the 20 W beam was successful
From the beginning to the end almost one month was necessary

15. YAG from inverse path: fringes
Probe beam from the inverse path
Probe beam superposed to a HeNe passing through the RFC in the lower part
Camera looking at the coils frame (hit by the RFC transmission): mode flashing visible
Secondary YAG beam
1 25 Hz pzt scanning
ccd
CCD and PhD looking at RFC reflection
ccd
photodiode

16. Contrast improvement and alignment
YAG probe Reflected beam
Contrast = 0.7

17. RFC alignment using PR alignment

18. RFC alignment using PR alignment

19. Near Field of M13 and Far Field
1m-f FF
Screens NF

20. Move M14 and observe overlapping with NF ccd
M14 movement
1m-f FF
Move M14 and observe overlapping with NF ccd NF

21. Correct with M13 to overlap on the FF ccd
M13 movement
1m-f
Correct with M13 to overlap on the FF ccd FF
Move M14 and observe overlapping with NF ccd NF

22. After alignment: the 20 W beam resonates in the RFC
ccd
PhD

23. The RFC transmission is not visible with the RFC aligned
Inverse path beam and direct beam are being superposed below acting on M13 and M4 mirrors
When superimposed both beams should resonate
ccd
PhD

24. RFC locked, reflected 20 W YAG beam: 1 March 2006
Good alignment +
longitudinal mismatching
Contrast = 54 %
(it was 80% before the shutdown)

25. RFC alignment: conclusion
The RFC alignment was more difficult than expected: the cavity axis was not where it was expected, maybe the RFC was not aligned inside its tank, or it had moved slightly during new IB assembling
The RFC is locked in a stable way, with the beam transmitted by the IMC: more stable with the alignment with respect to the previous setup
We cannot see the RFC transmission

26. Further activities on RFC
RFC locking filter change: a new filter has been implemented, which allows a reduction of the frequency noise of the prestabilized beam
RFC automatic alignment: this activity is going on; it will allow to keep the beam aligned on the RFC using the two closed loop pzt placed before the RFC. This allows shifts of the beam on the upper part, in order to better align the upper part optics, without losing the RFC alignment

27. Several problems/failure have occurred:
Problems encountered
Several problems/failure have occurred:
it has been necessary to open the IB tower twice
Wrong PSD
electronics
DPS misaligned
TS damaged
Beam clipped
PM stuck
RFC_trans clipped

28. Further activities involving the injection system
After the restart of the IB, some new features and other activities have been performed:
Beam Steering System
IMC matching improvement
IMC automatic alignment restarted
Input power stabilization (the photodiode measuring the IMC transmission has been changed)
RFC automatic alignment
PSD on the IB working (new homemade electronics)

29. BMS: DC quadrants, ABP actuation
BMS allows to keep beam aligned with respect to DC_quadrants placed on the External Injection Bench.
The signal from the DC quadrants is sent to the ABP (Automatic Beam Positioning) mirrors (pzt steered mirrors).
It allows a stable and repetitive positioning of the beam entering into the IMC;
It allows performing pure translations and angle of the beam.
ABPs
NF QF
FF QF
(on laser
bench)

30. With the help of BMS, IMC matching has been improved:
96% matching (it was 82%),
91% contrast (should correspond to about 1500 ppm losses in the IMC).
IMC transmission is now about 8 W (at about the same level as before the shutdown)
This power is entering into the ITF (we had 0.7 W entering into the ITF before the shutdown)

31. IMC automatic alignment
The AA of the MC is working again as before the shutdown (for the moment acting only on the MC mirror, correcting the FF_vert and the NF_horiz degrees of freedom.
The (new) AA of the IB is ready to be implemented: it should replace the LC of the IB

32. Power Stabilization
IMC_trans HF
Master laser
Diode current
Data from spectrum analyser is 50 times lower in the
100Hz region than dataDisplay measurent (above) (to be investigated)

33. RFC automatic alignment
RFC AA now
separated from IMC AA
M16
Wavefront sensing
quadrants on the EIB
Closed on the vertical DOF (1 Hz bandwidth)
Horizontal DOF not working (M16_PZT horiz. not working properly)

34. New PR mirror: monolithic and higher R (0.95 vs 0.925)
Comparison between the old (black) and new monolithic (red) PR mirror

35. II- ITF restart

36. IB LC after RFC locking
The IB LC filters were changed after restart: frequency noise was reintroduced

37. Frequency noise after RFC locking (ITF misaligned)
IB transfer function
Frequency noise

38. IB in high noise control IB in low noise control
IB LC filter upgrade
IB in high noise control
IB in low noise control
Blue curves: MC in high/low noise (factor 100 G difference)
Red curves: MC in high/low noise (factor 100 G difference)

39. MC-RFC locking filter: after restart
Too small G  SSFS couldn’t engage

40. Frequency noise after RFC locking (ITF misaligned)
Purple: C7
Black: after new IB RFC locking

41. New MC-RFC locking filter upgrade

42. New frequency noise: SSFS can engage

43. Frequency noise: C7 (beam attenuated) vs now

44. Now the full recycled ITF is being locked
ITF restart: locking
Since end of January:
Photodiodes gains readjusted for the higher power (10 times more than before shutdown)
Automatic alignment restarted:
Tested the drift control of the two cavities
Quadrant photodiodes gains adjusted
Not gone further because it needs the full locking of the ITF
PR-NI
PR-NE
CITF
NE-WE-BS NA WA
Recombined
SSFS
Variable Finesse with PR misaligned ….
Now the full recycled ITF is being locked

45. Beam Frequency stabilization
SSFS
B8p
B2_3f_ACp  PR (PRCL)
B1p_DC  BS (MICH)
B5_ACp  SSFS (CARM)
B8_ACp NE-WE (DARM) L1 L2 l1 l2
B2_3f_ACp
B5_ACp
SSFS using CARM for the
Beam Frequency stabilization l0
B1p_DC

46. The restart of SSFS required some gain tuning because:
SSFS restart
The restart of SSFS required some gain tuning because:
RFC locking filter was different
Frequency noise was different
RFC gains are different
After tuning readjustment, IB LC filters and RFC locking filter SSFS is now working properly

47. Towards the dark fringe
B8p
STEP 7
B2_3f_ACp  PR (PRCL)
B1p_DC  BS (MICH)
B5_ACp  SSFS (CARM)
B8_ACp NE-WE (DARM) L1 L2 l1 l2
B2_3f_ACp
B5_ACp
SSFS using CARM l0
B1p_DC
DF 0.05

48. ITF locking
Here we are
Status on 16th March: ITF locked up to step 7 (0.05 of the dark fringe)

49. Parabolic telescope T2: M6 mirror misalignment
3 closed loop picomotors
Tilted: tx (650 mrad) and ty (850 mrad)

50. Effect of M6 misalignment
M6 aligned (beam at 3 km)
M6 misaligned (beam at 3 km)
(Qx=650 mrad
Qy=850 mrad)

51. Resulting beam shape Beam size at NE: wx= 60mm wy= 60mm
Beam size on Cam5:
wx= 0.7mm
wy= 0.42mm
To fit these measurements, the beam parameters inside ITF with respect to BS position are (perfect matching for w=21.3, z=0):
wx= 15mm, zx= -400m
wy= 23mm, zy= 800m
The matching on the FP cavities should be around 89% in these conditions: confirmed by measurement (88%).
Beam parameters before shutdown:
wx= 18mm, zx= -500m
wy= 18mm, zy= 500m)

52. Short telescope T1 centeringDY L1
f=130 L2
f=-80
D=60mm
ccd

53. Beam shape after the Faraday isolator
Dy=2 mm Dw/w = 2%
Dy=4 mm Dw/w = 9%

54. Conclusion
The restart of the Injection System has required more than two months
The new Injection System is now working
The ITF is close to final locking with full power (8 W)
Some problems involving the new IB remain open:
The RFC matching is poor and the RFC transmission is not sent out of the IB tower
The astigmatism of the beam has to be corrected
For the moment the effort is in achieve the full locking again and, since we can go on in these conditions, to pospone the solving of this problems to a later moment