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VIRGO• LAPP – Annecy
• NIKHEF – Amsterdam
• INFN – Firenze-Urbino
• INFN – Frascati
• IPN – Lyon
• INFN – Napoli
• OCA – Nice
• LAL – Orsay
• ESPCI – Paris
• INFN – Perugia
• INFN – Pisa
• INFN – Roma
Status of theVIRGO Interferometer
S.Braccini – INFN Pisa
Part 1 – Introduction
Part 2 – Design
Part 3 – Commissioning
Part 4 – Future
VIRGO is a typical interferometric GW detector
hLL2
1
L m
h
(VIRGO Supernova)
L m
VIRGO is a typical interferometric GW detector
4gw L h
h = 10 -21 gw= 3·10 -11 rad
Fabry-Perot cavities to increase the effect
Increase beam phase shift by 2F
Optical Readout Noise
2 1 shot shot
ch
P L P
20 W 1 kW
An accurate measurement of the phaserequires a large amount of photons…
• Fluctuation-dissipation theorem
Thermal Noise
)(4)(~2 fTkfF B
Reduce dissipations in the optical payloads
to reduce thermal fluctuations
Seismic Noise
Suspend each mirror by a cascade of 6 dof oscillators
frequency
tran
smis
sion
Ground Seismic Vibrations
Summary of the technique
Low Dissipations
Fabry-Perot
photodiodeRecycling
High Power Laser
SeismicIsolation
Part 2 – VIRGO Design
VIRGO Optical Layout
20 WLaser
Input Mode Cleaner (144 m)
Output Mode
Cleaner
(4 cm)
Power Recycling
Fabry-Perot Cavities
(3 km)
VIRGO design sensitivity curve
Thermal Shot
Seismic
Injection System
A few Hzfrequency rms
stability is achieved in the input beam
Superattenuators
Blade springs
Magnetic antisprings
Extend the band down toa few Hz
6 m
MirrorGround
Dis
plac
emen
t (m
/Hz1/
2 )
Frequency (Hz)
Seismic Isolation
Thermal Noise
Measured
Upper Limit
Pitch
Yaw
Coil-MagnetActuators
Mirror Local Controls
Tens of rad
Fractions of rad
OpticalLever
Resonance Crossing
Mir
ror
Opt
ical
Sur
face
MIRRORSWING
Photodiode demodulated signal during resonance crossing
HOOK CAVITIES AT RESONANCE USING MIRROR COIL-MAGNET
ACTUATORS (Picometer Accuracy)
Interferometer Locking
Coils
Marionetta
MirrorReference Mass Beam
Suspension Last Stage
ReferenceMass
Mirror
Beam
Coils
Marionetta
MirrorGround
Dis
plac
emen
t (m
/Hz1/
2 )
Frequency (Hz)
Thermal Noise
Seismic Isolation
Low Frequency
Swing
Fixed Stars
ADC DSP DAC
Accelerometers
Coil-Magnet Actuators
Inertial Damping
Fixed Stars
Inertial Damping
Mir
ror
Opt
ical
Sur
face
Mirror swing reducedfrom several m/s
to a fraction of m/s
Enough to allow locking acquisition
Summary
Seismic Noise Suppression
above 4 Hz
Damp angular swings by local controls (10-7 rad) to allow a good
interference
Reduce longitudinal swing by
Inertial Damping (0.5 m/s)
to allow locking
Mir
ror
Opt
ical
Sur
face
Pre-Stabilized Beam Source (a few Hz)
Part 3 - Commissioning
RECYCLING CAVITY = l0 + (l1+ l2)/2
4 degrees of freedom to be controlled
(“locked”)
l2
l1
MICHELSON = l1- l2 COMMON ARM LENGTH = L1+ L2
L2
L1
DIFFERENTIAL ARM LENGTH = L1- L2
l0
Interferometer Locking
l2
l1
L1
L2
l0
Variable Finesse Locking Acquisition
L1
L2
l2
l1
l0
Low Finesse of Recycling Cavity
Arm cavity fields do not mix
Dark Port DC signal
Variable Finesse Locking Acquisition
PR Mirror rotatedby 100 microrad
50 % Interference(Gray Fringe)
Easy preliminary locking(mirror swing is stopped)
Pick-offLaser Frequencyfollows CARM motion
L1
L2
l2
l1
l0
Dark Port DC signal
Variable Finesse Locking Acquisition
Put in action the“Second Stage Frequency
Stabilization Loop”
Common Arm motionis controlled by laserwith high accuracy
L1
L2
l2
l1
l0
Dark Port DC signal
Variable Finesse Locking Acquisition
Pick-offLaser Frequencyfollows CARM motion
Slow Alignment ofthe Recycling Mirror
L1
L2
l2
l1
l0
Dark Port DC signal
Variable Finesse Locking Acquisition
Slow Alignment ofthe Recycling Mirror
Pick-offLaser Frequencyfollows CARM motion
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-0.5
0
0.5
1
L1
L2
l2
l1
l0
Dark Port DC signal
Variable Finesse Locking Acquisition
Slide to DarkFringe
DC-0.01 HzTide control
0.01-5 Hz
5-50 Hz
Hierarchical Control
millimiters
fractions of micron
nm
Actuators engender a noise floor proportional to the amplitude of
their force range
Only nm displacements can be compensated at the mirror level
Use Quadrant Photodiodes toClose Automatic Alignment
AfterLocking….
10-7 10-9 rad
Single armSingle armSingle armRecombinedRecycledRecycledRecycled
VIRGO run sensitivities
LIGO and VIRGO
Dut
y C
ycle
(%
)
Time (days)
Duty Cycle during C6 run
VIRGO Horizon
Horizon NS/NS – Optimal Incidence
1 day
Measure the sensitivity Identify the noise sources Try to reduce the noise
C6
ImprovementsAutomatic Alignment
New Filter for Recycling Control
Subtraction of Beam Splitter Control Noise
Reduction of laser frequency noise
2kHz bump due to detection tower pump (exciting external bench)
Less dynamics for BS correction
Noise Hunting
Control Noise
Photodiode Noise
C7 Run Noise Budget
IncidentBeam 12 cm
Translations induce
beam jitters
Recycling Transfer Function
The problem of power recycling mirror
350 mm
New monolithic flat power recycling mirror
Recycling Transfer Function
OldNew
Laser Frequency Noise (After Mode Cleaner)Power Recycling
Mirror Misaligned
Power Recycling
Mirror Aligned
Suppress back-scattered light
Hz
Time
Faraday Isolator on Input Bench
Up to now VIRGO operated with a reduced power
(from 7 W down to 700 mW) Limited Sensitivity in High Frequency Range
The problem of back-scattered light
New injection bench
Interferometer locked
Interferometer now in action with 7 W input power
Faraday isolation ~ 100 (nominally much larger but enough)
New Injection Bench Performance
Mode Cleaner Transmission signal (Now)Mode Cleaner trasmission signal (Before)
Reduction of sidebands power by a factor ~ 4 (time constants ~ a few minutes)
A New Problem - The thermal effect
10 min
CARRIER POWER SIDEBAND POWER
A New Problem - The thermal effect
Lock is kept for long periods despite of this problem
10 hours
SIDEBAND POWER CARRIER POWER
15 min
SIDEBAND POWER CARRIER POWER
The Present Status
* Interferometer locked for a long period with 7 W input power
* 10 dof of automatic alignment controlled
* Sensitivity curve measured and noise hunting restarted
Just a “technical sensitivity” curveto show that itf restarted
C7
Now
Part 4 – The Future
2006: Noise reduction Reach design sensitivity above 100 Hz
2007: Scientific Run (stop for upgradings ?)
2008: VIRGO+ assembly and commissioning
NETWORK AGREEMENT AND JOINT ANALYSIS
Plans for next years
Thermal Shot
Seismic
50 W laserMonolithic Suspensions
VIRGO + Improvements
VIRGO + Design Sensitivity
1 10 100 1000 1000010-23
10-22
10-21
10-20
10-19
h
(f)
[1/s
qrt
(Hz)
]
Frequency [Hz]
(a) Virgo + (b) Virgo + (old mirror th. noise model) (c) Nominal Virgo (d) Pendulum Thermal Noise (e) Mirror Thermal Noise (f) Optical Readout Noise
(a)
(b)
(c)
(d)
(e)
(f)
VIRGO+
VIRGODESIGN
First Generation Sensitivity
10-24
10-23
10-22
10-21
10-20
10-19
10-18
1 10 100 1000 104
VIRGO
LIGO
Resonant Antennas 2007
Hz
GEO
Core Collapse@ 10 Mpc
BH-BH MergerOscillations@ 100 Mpc
Pulsars
hmax, 1 year integration
BH-BH Inspiral,z = 0.4
BH-BH Inspiral, 100 Mpc
QNM from BH Collisions, 1000 - 100 Msun, z=1
NS, =10-6 , 10 kpc
QNM from BH Collisions, 100 - 10 Msun, 150 Mpc
NS-NS Inspiral, 300 Mpc
NS-NS MergerOscillations@ 100 Mpc
UnlikelyDetection
h~
h
10-24
10-23
10-22
10-21
10-20
10-19
10 100 1000 104Hz
Core Collapse@ 10 Mpc
NS-NS MergerOscillations@ 100 Mpc
BH-BH MergerOscillations@ 100 Mpc
Pulsars
max, 1 year integration
BH-BH Inspiral,z = 0.4
BH-BH Inspiral, 100 Mpc
QNM from BH Collisions, 1000 - 100 Msun, z=1
NS, =10-6, 10 kpc
QNM from BH Collisions, 100 - 10 Msun, 150 Mpc
NS-NS Inspiral, 300 Mpc
VIRGO +
SFERA
(Canceled)
DUAL Demonstrator (2011)
LIGO+h~ Likely
Detection
Upgraded Network (2008-2012)
h
GEO-HF(2009/10)
Next Generation
Advanced Virgo (2012)
• Design activity still not started
• R&D activities on• High power lasers• Signal recycling and optical topologies• Coatings• Electrostatic actuators
Part 4 - Future
Advanced Virgo White Paper VIR–NOT–DIR–1390–304
Beyond 2012
10-25
10-24
10-23
10-22
10-21
10-20
10 100 1000 104
Advanced Virgo
Hz
Core Collapse@ 10 Mpc
NS-NS MergerOscillations@ 100 Mpc
BH-BH MergerOscillations@ 100 Mpc
SFERA QND
Pulsarsh
max, 1 year integrationLCGT-I
3rd Generation ITF
BH-BH Inspiral,z = 0.4
BH-BH Inspiral, 100 Mpc
QNM from BH Collisions, 1000 - 100 Msun, z=1
NS, =10-6 , 10 kpc
QNM from BH Collisions, 100 - 10 Msun, 150 Mpc
AdvancedLIGO
NS-NS Inspiral, 300 Mpc
DUAL SiC
SFERA QL
Detection is “sure”h~
Beyond 2012
NS/NS detectable
@ hundreds of Mpc
ITF+ 2009
Advanced VIRGO-LIGO2013
VIRGO-LIGO 2006
Virgo
Now: VIRGO is again in action with 7 W input beam
Conclusions
2006: End of commissioning
2007: Scientific Run with a sensitivity comparable to LIGO
Open Problems: Thermal compensation, Low frequency control noise
1st GENERATION NETWORK IS IN ACTION !
…. VIRGO+ (2009) and VIRGO Advanced (2012-13)
The End
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
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
• 1. Mirror excitation in windy conditions– => more frequent unlocks when weather is bad
• 2. DAC noise on mirror actuation coils– High 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
Suspension: inertial damping modification
L(s)H(s)
L+H = 1
accelerometer
LVDT
• Inertial damping– Inverted pendulum top platform is immobilized by– HF accelerometers (inertial sensors)– LF LVDT’s (ground based) => introduce seismic noise
• Solution– Reduced HF/LF cross-over frequency to 30 mHz– Not so simple ... (see G. Losurdo’s talk)
LVDT = linear variable differential transformer
30 mHz
Thermal effects
10 min
Reduction of sidebands power by a factor ~4
Time constants ~ a few minutes
Power reduction planned at the beginning of June
Study of the effect by simulation and experimental measurements (scanning Fabry-Perot)
LIGO-Virgo Run Planning
• The agreement foresee also a run coordination– “A Joint Run Planning Committee will be formed, consisting
of the Virgo and LSC Data Analysis Coordinators, plus relevant experts from Virgo, GEO, and LIGO on topics such as: calibration, detector characterization/vetoes, detector planning, commissioning, and site management…”
• Start sketching a possible joint run planning
VERY PRELIMINARY
Part 3
VIRGO Future
CERN – C.A.P.P. workshop – June 16th, 2003 G.Losurdo – INFN Firenze-Urbino
Sensitivity improvement
• The nominal Virgo sensitivity is dominated by– the shot noise, at high frequency– the pendulum thermal noise at low frequency
1 10 100 1000 1000010-23
10-22
10-21
10-20
10-19
10-18
(a) Virgo Nominal sensitivity (b) Seismic noise (c) Pendulum thermal noise (d) Mirror thermal noise (e) Shot Noise
h(f) [1/
sqrt(H
z)]
Frequency [Hz]
(a)
(b)
(c)
(d)
(e)
VIRGO intende raggiungerla nei prossimi mesi