the commissioning of the virgo interferometer
DESCRIPTION
The commissioning of the Virgo interferometer. H. Heitmann Observatoire de la C ô te d’Azur, Nice for the VIRGO collaboration. Evolution of commissioning Upgrades Recent commissioning activities Outlook. Status of commissioning before shutdown. Commissioning sensitivity evolution. - PowerPoint PPT PresentationTRANSCRIPT
1 GWADW Elba 30.05.2006
The commissioningof the Virgo interferometer
H. Heitmann
Observatoire de la Côte d’Azur, Nice
for the VIRGO collaboration
• Evolution of commissioning
• Upgrades
• Recent commissioning activities
• Outlook
2 GWADW Elba 30.05.2006
Status of commissioning before shutdown
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Commissioning sensitivity evolution
Run C7duty cycle 64%14 h lock
Run C6duty cycle 90%40 h lock
Single armSingle armSingle armRecombinedRecycledRecycledRecycled
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Problems with configuration up to C7
Fringes due to backscattering in mode cleaner=> Operate with reduced power (10%)
Non-monolithic, curved power recycling mirrorResonances => Control problemsShift sensitivity => alignment drifts
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Recent upgrades
• New power recycling mirror
• New injection bench
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VIRGO layout
Injection bench (IB)
Power recycling mirror
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Power recycling mirror
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120 mm
R=4100 mm
350 mm
Translations induce misalignment and jitter noiseflat mirror
Old power recycling mirror
PR mirror is • non-monolithic• curved (part of beam matching telescope)
Incident Beam
PR mirror transfer function
9 GWADW Elba 30.05.2006
New power recycling mirror
Monolithic mirrorNo more internal resonances in the control band !!
Flat surfaces=> no more lens effect (no more part of input telescope)=> larger beam coming out of injection bench => parabolic telescope needed on IB
PR mirror transfer function
OldNew
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Injection bench
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Laser Frequency Noise
Power Recyclingmirror misaligned
Power Recyclingmirror aligned
Hz
Time
Fringes in the interferometer
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Origin of the fringes
Backscattering in the mode cleaner
for enabling power recycling (C7 configuration)
Faraday Isolator needed on theinjection bench for full power operation
Injected power lowered to 700 mW
Laser lightBackscattered light
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10% reflectivitymirror
Old injection bench
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New injection bench
Main requirements:• Faraday isolator• Parabolic output telescope• Thinner suspension wires
more suitable resoance frequencies
15 GWADW Elba 30.05.2006
New injection bench (OptoCad design)
Design and realizationEGO optics group
Parabolic outputtelescope
Faradayisolator
From laser
To interferometer
Mode cleaner
16 GWADW Elba 30.05.2006New injection bench (above)
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Referencecavity
New injection bench (below)
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New injection bench status
Bench isinstalledalignedcontrolled
Beamoutput power 7 W (10x C7)matching: coupling into arm cavities 95-97%
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Some recent commissioning activities
• The variable finesse locking technique
• Mode cleaner mirror radiation pressure
• Suspension improvements
• New injection system autoalignment
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The variable finesse locking technique
21 GWADW Elba 30.05.2006
Locking: Step 1
WE
NENI
WI
BSPR
• Power recycling mirror misaligned
=> no signal mixing
• Each cavity locked independently
• ITF output at « grey fringe » (50%)
Recombined interferometer
North arm
West
arm
50%
ControlsNE North cav. transmission PWE West cavity transmission PBS Dark fringe power DC
22 GWADW Elba 30.05.2006
WE
NENI
WI
BSPR
• Laser locked on ITF common mode very high bandwidth loop
=> get rid of dominating
common mode signal
Recombined interferometer
North arm
West
arm
40%
ITF common mode
ControlsNE-WE North cav. transmission PBS Dark fringe power DClaser Recycling cavity pick-off PPR ITF reflection (3) P
Locking: Step 2
23 GWADW Elba 30.05.2006
WE
NENI
WI
BSPR
• Power recycling mirror aligned
Recycled interferometer
North arm
West
arm
ITF common mode
40%
ControlsNE-WE North cav. transmission PBS Dark fringe power DClaser Recycling cavity pick-off PPR ITF reflection (3) P
Locking: Step 3
24 GWADW Elba 30.05.2006
WE
NENI
WI
BSPR
• Stepwise going down to dark fringe
Recycled interferometer
North arm
West
arm
ITF common mode
5%
ControlsNE-WE North cav. transmission PBS Recy.cav. pick-off Q laser Recy.cav. pick-off PPR ITF reflection (3) P
Locking: Step 4
25 GWADW Elba 30.05.2006
WE
NENI
WI
BSPR
0%
North arm
West
arm
ITF common mode
• Dark fringe reached
Recycled interferometer
ControlsNE-WE Dark fringe PBS Recy.cav. pick-off Q laser Recy.cav. pick-off PPR ITF reflection (3) P
Locking: Step 5
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Mode cleaner mirror: radiation pressure
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Mode cleaner mirror: radiation pressure effect
Frequency increase
y
MC locked full power MC locked 60% powerMC unlocked
x: 2.13 -> 1.97 Hz
y: 1.27 -> 2.0 Hz
mirror dimensions: 30x80 mm360 grams
Mode position changes with mirror alignment extra torque resonance frequency change
Problem:• Autoalignment loops became unstable• Corrector adaptation was needed
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Recent mirror suspension improvements
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Suspension: recent problems and solutions
30 mHz
acce
lero
met
er
ground-based
sensorsGround-independent control above 30 Hz
Mirror excitation with bad weather less stable lock
Changed suspension top stage control seismic
acceleration
noisy daycalm day
Micro-seismic peak(sea waves)
DAC noise on mirror actuation coils
Hierarchical control Rearrange forces going to the suspensionSwitch to low-noise coil drivers
Contr
ibuti
on t
o c
ontr
ol
(See talk by G. Losurdo)
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New injection system autoalignment
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Injection system autoalignment
Old systemIdea: if IB is rigid, no misalignments
(turned out not to be true)
IB under local control
New systemBeam aligned on fixed mechanical reference (external bench)Mode cleaner fully aligned on beamAutocentering of beam onto MC end mirror
Future enhancementBeam aligned on 3 km target
10%
2004
Mode cleaner transmitted power fluctuations
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MATRIX
Old injection system autoalignment layout
Ref. cav.
MCmirror
Laser
M5
M6
Ref. cav. autoalignment
MATRIX
Injection bench
MC mirror autoalignment--Inj.B. local control--Beam autoalignment--
IB Coils
MCAA
Picomotors
Piezos
Wavefront sensors
33 GWADW Elba 30.05.2006
MATRIX
New injection system autoalignment layout
Ref. cav.
MCmirror
Laser
M5
M6
MATRIX
RFC AA
Beam prealignment
MATRIX
MC IBAA
IB Coils
Ref.cav. autoalignment
Picomotors
Piezos
--
Injection bench
MC mirror autoalignment--Inj.B. autoalignment--Beam autoalignment--
DC position sensors
Wavefront sensors
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Outlook
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Present status
Full locking of interferometer1-2 hours locking periodsor 5 minutes …
Thermal effectsAffect recycling cavity stability(modulation sidebands drop)
30-50 Hz burst events (skeephs)Locking stability problems
Misalignment sensitivity?Hasten full autoalignment (5/10 d.o.f. OK)
2h0 1000 2000 3000 4000 5000 6000 7000
0.00
0.01
0.02
0.03
0.04
0.05
0.06
-2.0x10-5
0.0
2.0x10-5
4.0x10-5
6.0x10-5
8.0x10-5
1.0x10-4
1.2x10-4
1.4x10-4
1.6x10-4
1.8x10-4
2.0x10-4
2.2x10-4
2.4x10-4
Pr_
B5_D
C
time [s]
Pr_B5_DC_mean
Pr_B5_2f_ACq_mean
Carrier power
Sideband power
Time 0
Thermal effects in rec. cavity
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Next steps
Improve sensitivityLow frequency
control noise (alignment)modulation frequency tuning (servo)
Medium frequencyscattered lightacoustic shielding in laser lab
High frequencyincreased powernew low-noise HF modulation generator
New MC mirrorbetter surface qualitylower losseslarger, heavier?
avoid radiation pressure problemsfacilitate control
...
End
End
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Old injection bench (OptoCad design)
10% reflectivitymirror for power reduction
From laser
To interferometer
Mode cleaner
39 GWADW Elba 30.05.2006
14 hours locked
C7 (5 days Sept. 2005)
40 hours locked
Duty Cycle of last two commissioning runs
C6 (14 days Aug. 2005)
40 GWADW Elba 30.05.2006
1. Mirror excitation in windy conditions=> more frequent unlocks when weather is bad
2. DAC noise on mirror actuation coilsHigh force needed for lock acquisition=> bad DAC dynamics in steady conditions (low force)
Micro-seismic peak(sea waves)
Suspension: recent problems
seismic acceleration
wind speed
susp displacement
noisy daycalm day
41 GWADW Elba 30.05.2006
Suspension: inertial damping modification
L(s)H(s)
L+H = 1
accelerometer
LVDT
Inertial dampingInverted pendulum top platform is immobilized byHF accelerometers (inertial sensors)LF LVDT’s (ground based) => introduce seismic noise
SolutionReduced HF/LF cross-over frequency to 30 mHzNot so simple ... (see G. Losurdo’s talk)
LVDT = linear variable differential transformer
30 mHz
42 GWADW Elba 30.05.2006
Suspension: hierarchical control
DC-0.01 HzTide control
0.01-5 Hz
5-50 Hz
After lock acquisition: reduction of mirror actuator gain=> reduction of DAC noise
Initial condition:-lock acquisition-all force goes to mirror
Static condition:-interferometer locked-force split according to frequency bands
DAC noise
43 GWADW Elba 30.05.2006
1.4 Mo coalescence detection range
M31 (Andromeda) 700 kpc
C7 (19 Sept 05)
C6 (12 Ago 05)
Environmental disturbance re-injection through the control system
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C7 noise budget
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Mirror centering
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Mirror centering
Needed because of astigmatism and suspected beam clipping
Advantage: learned techniques for mirror centering Necessary for reducing alignment noise which limits us at low frequencies
Two techniques usedVisual centering
Where possible…
Mirror shaking at natural resonanceFind frequency in longitudinal motion (locking error signal)
x
47 GWADW Elba 30.05.2006
Beam splitter visual centering
Before centering After centering
cm
cm
Mirror
Coil
Local control camera imageobservation of diffused beam spot while moving mirror