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