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VIRGO commissioning progress
Paolo La Penna
for the VIRGO collaboration
European Gravitational Observatory
N5-WP1 8TH MEETING, Frascati, 20/03/2006
Virgo Commissioning Status
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Status in December 2005
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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
(http://www.ego-gw.it/ILIAS-GW/WP1docs/lapenna_121205.ppt)
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Since then:
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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
N5-WP1 8TH MEETING, Frascati, 20/03/2006
Virgo Commissioning Status
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I – Injection system restart
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Operation performed on the Injection System
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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
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Virgo Commissioning Status
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Changes in Virgo after September shutdown
PR mirror
IB+RFC
EIB
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Injection system
Lower stage
Upper stage
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Difference old-new IB
Old IB
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New IB
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IMC alignment: december 2005
HeNe autocollimation on the MC mirror
Acting on the IB alignment
(checked with a ccd)
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IMC alignment: december 2005
laser
YAG beam direct beam centering
on the MC mirror acting on the
external steering mirrors
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IMC alignment: december 2005
laser
MC mirror alignment
until IMC resonances are visible
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IMC locking: december 2005
laser
Pout  8 W
IMC locking
Feedback on laser pzt
using the reflection as a trigger
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ITF alignment: 13 january 2006
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RFC alignment and locking: february 2006
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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
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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
ccd
Secondary YAG beam
1 V @ 25 Hz pzt scanning
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 CCD and PhD looking at
RFC reflection
Virgo Commissioning Status
ccd
photodiode
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Contrast improvement and alignment
YAG probe Reflected beam
Contrast = 0.7
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RFC alignment using PR alignment
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RFC alignment using PR alignment
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Near Field of M13 and Far Field
1m-f
FF
Screens
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NF
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M14 movement
1m-f
FF
Move M14 and observe overlapping with NF ccd
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NF
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M13 movement
1m-f
FF
Correct with M13 to overlap on the FF ccd
Move M14 and observe overlapping with NF ccd
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NF
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After alignment: the 20 W beam resonates in the RFC
ccd
PhD
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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
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RFC locked, reflected 20 W YAG beam: 1 March 2006
Contrast = 54 %
(it was 80% before the shutdown)
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Good alignment
+
longitudinal mismatching
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RFC alignment: conclusion
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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
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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
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We cannot see the RFC transmission
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Further activities on RFC
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RFC locking filter change: a new filter has been
implemented, which allows a reduction of the
frequency noise of the prestabilized beam
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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
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Problems encountered
Several problems/failure have occurred:
it has been necessary to open the IB tower twice
DPS misaligned
Wrong PSD
electronics
TS damaged
Beam clipped
PM stuck
RFC_trans clipped
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Further activities involving the injection system
After the restart of the IB, some new features and other
activities have been performed:
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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)
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BMS: DC quadrants, ABP actuation
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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)
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IMC matching
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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).
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IMC transmission is now about 8 W (at about the
same level as before the shutdown)
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This power is entering into the ITF (we had 0.7 W
entering into the ITF before the shutdown)
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IMC automatic alignment
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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.
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The (new) AA of the IB is ready to be implemented: it
should replace the LC of the IB
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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)
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RFC automatic alignment
M15
RFC AA now
separated from IMC AA
M16
Wavefront sensing
quadrants on the EIB
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Closed on the vertical DOF (1 Hz bandwidth)
Horizontal DOF not working (M16_PZT horiz. not working properly)
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New PR mirror: monolithic and higher R (0.95 vs 0.925)
Comparison between the old (black) and new monolithic (red) PR mirror
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II- ITF restart
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IB LC after RFC locking
The IB LC filters were changed after restart: frequency noise was reintroduced
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Frequency noise after RFC locking (ITF misaligned)
IB transfer function
Frequency noise
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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)
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MC-RFC locking filter: after restart
Too small G  SSFS couldn’t engage
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Frequency noise after RFC locking (ITF misaligned)
Purple: C7
Black: after new IB RFC locking
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New MC-RFC locking filter upgrade
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New frequency noise: SSFS can engage
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Frequency noise: C7 (beam attenuated) vs now
Now
C7
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ITF restart: locking
Since end of January:
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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
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SSFS
B8p
B2_3f_ACp  PR (PRCL)
B1p_DC  BS (MICH)
B5_ACp  SSFS (CARM)
B8_ACp NE-WE (DARM)
L1
l1
l2
L2
B2_3f_ACp
l0
SSFS using CARM for the
Beam Frequency stabilization
N5-WP1 8TH MEETING, Frascati, 20/03/2006
B5_ACp
B1p_DC
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SSFS restart
The restart of SSFS required some gain tuning because:
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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
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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
l1
l2
B2_3f_ACp
L2
l0
SSFS using CARM
B5_ACp
B1p_DC
N5-WP1 8TH MEETING, Frascati, 20/03/2006
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DF 0.05
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ITF locking
Here we are
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Status on 16th March: ITF locked up to step 7 (0.05
of the dark fringe)
N5-WP1 8TH MEETING, Frascati, 20/03/2006
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Parabolic telescope T2: M6 mirror misalignment
3 closed loop picomotors
Tilted: tx (650 mrad) and ty (850 mrad)
N5-WP1 8TH MEETING, Frascati, 20/03/2006
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Effect of M6 misalignment
M6 aligned (beam at 3 km)
M6 misaligned (beam at 3 km)
(Qx=650 mrad
Qy=850 mrad)
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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)
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Short telescope T1 centering
DY
L1
L2
f=130 f=-80
D=60mm
ccd
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Beam shape after the Faraday isolator
Dy=2 mm
Dw/w = 2%
N5-WP1 8TH MEETING, Frascati, 20/03/2006
Dy=4 mm
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Dw/w = 9%
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Conclusion
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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:
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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
N5-WP1 8TH MEETING, Frascati, 20/03/2006
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