The Virgo interferometer for Gravitational Wave detection and its upgrade

Francesco Fidecaro

The First Galileo-Xu Guangqi Meeting

Shanghai, October 26, 2009

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Outline• The Virgo Collaboration• The European Gravitational Observatory• The Virgo interferometer• The LSC Virgo agreement• Performance• Upgrades

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The Virgo Collaboration• Early efforts

– Brillet (optics)– Giazotto (suspensions)

• Collaboration started in 1992• LAPP Annecy• EGO Cascina• Firenze-Urbino• Genova• Napoli• OCA Nice• NIKHEF Amsterdam• LAL Orsay• LMA Lyon – ESPCI Paris• APC Paris• Perugia• Pisa• Roma La Sapienza• Roma Tor Vergata• Trento-Padova• Warsaw• RMKI Budapest (observers)• LKB Paris (observers)• 18 groups• About 200 authors

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The Virgo interferometer

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Issues in sensitivity (Virgo example)• h ~ 3 x 10-21 Hz-1/2 @ 10 Hz

• h ~ 7 x 10-23 Hz-1/2 @ 100 Hz

200 m fused silica suspension fibre

pioneered by Glasgow/GEO600

Mirror coating

Mirror thermal lensing compensation for high power

Seismic attenuation

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Virgo site in Cascina

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The European Gravitational ObservatoryPURPOSE• The Consortium shall have as its purpose the promotion of research

in the field of gravitation in Europe. • In this connection and in particular, the Consortium pursues the

following objectives:– ensures the end of the construction of the antenna VIRGO, its

operation, maintenance and the upgrade of the antenna as well as its exploitation;

– ensures the maintenance of the related infrastructures, including a computer centre and promotes an open co-operation in R&D;

– ensures the maintenance of the site;– carries out any other research in the field of gravitation of common

interest of the Members;– promotes the co-operation in the field of the experimental and

theoretical gravitational waves research in Europe;– promotes contacts among scientists and engineers, the dissemination of

information and the provision of advanced training for young researchers.

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World wide GW network: LV agreement• “Among the scientific benefits we hope to achieve from

the collaborative search are:– better confidence in detection of signals, better duty cycle and

sky coverage for searches, and better source position localization and waveform reconstruction. In addition, we believe that the intensified sharing of ideas will also offer additional benefits.”

• Collaborations keep their identities and independent governance

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LV Agreement (I)• “All data analysis activities will be open to all members of

the LSC and Virgo Collaborations, in a spirit of cooperation, open access, full disclosure and full transparency with the goal of best exploiting the full scientific potential of the data.”

• Joint committees set up to coordinate data analysis, review results, run planning, and computing. The makeup of these committees decided by mutual agreement between the projects.

• Joint publication of observational data whether data from Virgo, or LIGO (GEO) or both

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The low frequency strategy

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Noise in mass position

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Seismic isolation• Super-attenuators: multi-

stage passive seismic isolation system (many exchanges of visits with UWA group)

• Inverted pendulum: large amplitude low frequency motion for tidal control

• Mechanical filters in 6 dof• Hierarchical actuation:

F0, marionetta, mirror

MODEL

marionetta

mirror

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marionetta

mirror

Superattenuator performance• Excitation at top• Use Virgo sensitivity

and stability• Integrate for several

hours• Upper limit for TF at

32 Hz:1,7 10-12

• In some configurations a signal was found, but also along a direction perpendicular to excitation: compatible with magnetic cross talk

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The optics strategy

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Coating facility – LMA Lyon ESPCI Paris• Dedicated investment by Virgo• Large area coating• Metrology• Corrective coating procedure

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Virgo mirror performanceCoating Nature

and Clear aperture (mm)

RMS Wavefront (nm)Average

Absorption (ppm)

Average Scattering

(ppm)Transmission

Side A Side B Side A Side B

North End Mirror

-HR

330 mm3.9

150 mm3.8

150 mm0.67

150 mm4

150 mm42.9 ppm

West End Mirror -HR

330 mm2.8

150 mm3.4

150 mm0.69

150 mm6.5

150 mm38.3 ppm

North Input Mirror

HR 200 mm

AR 200 mm

2.6 60 mm

3.8 60 mm

1.2560 mm

560 mm

11.80 %

West Input Mirror

AR 200 mm

HR 200 mm

2.6 60 mm

2.5 60 mm

1.2060 mm

860 mm

11.66 %

Recycling Mirror 2006

HR 200 mm

AR 200 mm

1.4 60 mm

1.08 60 mm

0.54100 mm

860 mm

5.13 %

Beam Splitter n°1

AR 210 mm

HR 210 mm

3.9 100 mm

5.4 120 mm

1.35center

5.5100 mm

49.8 %

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Upgrades from VSR1 (2007)

to VSR2 (2009-2011)

Virgo+ upgrade: injection system• New laser amplifier (LZH): up to 50 W (25 W at interferometer input)

• New pre-mode-cleaner• Remotely tunable in-vacuum Faraday Isolator• Heavier input-mode-cleaner end-mirror

High power operation• Power increased in steps from 8 W (VSR1) to 17 W now

– limited by mismatching of reference cavity due to thermal effects• No major problems with interferometer stability• Some alignments loops more critical• Quadrature signals (B1_ACq or B5_ACq) kept close to zero using slow servos on TCS power• Currently about 1.5 W on both mirrors: interferometer similar to 8W• 'Cold interferometer' with about 2x 6W

– More optical gain, ideal frequency stabilization TF, but TCS too noisy

without TCS with TCS

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Noise understanding

• Noise sources and coupling are well understood

• Low frequency shows more structures

• Noise reduction in advanced detectors achieved with proper design

• Virgo+ in 2010: fused silica suspensions and higher Finesse– risk reduction for

Advanced detectors

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Virgo sensitivity progress

VSR1: May 18-Sep 30 2007 4 month continuous data taking simultaneously with LIGO Analysis in progress

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Very latest sensitivity

Calibration lines moved

Environmental noise

Stability• Robust interferometer

– 95% Science Mode duty cycle (if no commissioning is made)

– Good sensitivity• Stable horizon:

8-8.5 Mpc (1.4-1.4 Ns-Ns) - averaged

(now 8-9.5 Mpc)

42-44 Mpc (10-10 BH-BH) - averaged – fluctuating with input mirror etalon

effect• Low glitch rate: factor 10 lower than VSR1• Taking data since July 7th with 80% duty

cycle in science mode and locks alasting days

• Preparing for installation of monolithic suspensions

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Data Analysis

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Joint LIGO/Virgo Search for GRBs• Gamma Ray Bursts (GRBs) - brightest EM emitters in the sky

– Long duration (> 2 s) bursts, high Z progenitors are likely core-collapse supernovae

– Short duration (< 2 s) bursts, distribution about Z ~ 0.5 progenitors are likely NS/NS, BH/NS, binary merger

– Both progenitors are good candidates for correlated GW emissions!

• 212 GRBs detected during S5/VSR1– 137 in double coincidence (any two of LIGO Hanford, LIGO Livingston, Virgo)

• No detections, we place lower limits on distance assuming EGW = 0.01 Mc2

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VSR2 sensitivity for CW searches

Targeted searches.

Vela

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5

5

5

4

4-

3

3

4

sup

109.8 04.124 6910-J0537

108.7 56.59 Crab

105.7 68.55 1011J1913

101.1 58.50 3252J1952

108.9 46.38 2809-J1747

101.1 32.32 1034-J1833

104.1 44.30 6449J0205

100.8 38.22 Vela

Name

gwf

Compatible with some ‘exotic’ EOS

Marginally compatible with standard EOS

(Vela spin-down limit in ~80 days)

may improve on Crab

VSR2 sensitivity

Spin-down limit can be beaten for a few pulsars

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Monolithic fused silica suspension

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Silica anchors

Silica Clampson the marionette

Coupling to the mirror flats with New Ears

Silicate bonding

Steel box to host the upper silica clamp on the marionetta

Monolithic Suspensions

Clamp design

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Summary• After many years of blood, sweat and tears, Virgo is now

working very well• The low frequency region appears to be well understood

and other project will be able to profit from the experience;

• Not only seismic, but all environmental noise has to be mitigated

• We look forward trying to push further down the noise with the monolithic suspensions as it could give to the LV network a Poisson rate for NSNS coalescences of more than one event per year.

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The Fluctuation-Dissipation Theorem