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Plans for Advanced Virgo
Raffaele Flaminio
LMA/CNRS
on behalf of the Virgo Collaboration
SUMMARY
- Motivations
- Detector design
- Expected sensitivity
- Status and timeline
Marcel Grossman 12, Paris, July 13th 2009
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Virgo commissioning history


Virgo just started its second science run (VSR2)
Detector close to the design sensitivity
 BNS range > 8 Mpc (design is ~12 Mpc)
Marcel Grossman 12, Paris, July 13th 2009
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Virgo noise budget
Actuation
Eddy currents
Magnetic
Scattered light
Suspension thermal
SHOT
Mirror thermal



Noise budget well understood
Sensitivity close to fundamental noises
Large
improvements
need
Marcel Grossman
12, Paris, July 13th
2009large hardware modifications: Advanced Virgo
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Motivations for Advanced Virgo

Present detectors are testing upper limits of theoretical predictions

Even in the optimistic case expected rates
are too low to start GW astronomy
Enhanced LIGO/Virgo+

Need to improve the sensitivity

Upgrade Virgo to a 2nd generation
detector
Virgo/LIGO
108 ly
 Sensitivity: 10x better than Virgo
 Detection rate: ~1000x better

Be part of the 2nd generation GW
detectors network
 Timeline: commissioning to start in 2014.
 Make science with Advanced LIGO
Adv. Virgo/Adv. LIGO
Credit: R.Powell, B.Berger
Marcel Grossman 12, Paris, July 13th 2009
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Advanced Virgo Science Case


1 day of AdVirgo data ~ 3 years of Virgo data
Coalescing binaries detection rates
 BNS ~ 10/yr
 BBH ~ 0.1 - 100/yr (model dependent)

Advanced Virgo in the network:
 Much better event reconstruction
» Source location in the sky
» Reconstruction of polarization components
» Reconstruction of amplitude at source and determination of
source distance (BNS)
 Detection probability increases: 40% more events than
Advanced LIGO only
 Detection confidence increase (coincidence techniques)

Multi-messenger opportunities
 Collaboration with E.M. and v detectors will increase the
search sensitivity or equivalently detection confidence
 Advanced GW network opens new perspectives for
Astroparticle Physics

The experimentalists view
 After ten years of R&D, technology for a major
improvement has been demonstrated
Marcel Grossman 12, Paris, July 13th 2009
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Advanced Virgo design
Marcel Grossman 12, Paris, July 13th 2009
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Optical configuration and readout

Main drivers
 Reduce impact of quantum noise
 Mitigate coating thermal noise
 Allow for sensitivity tunability

Use of signal recycling
 Foreseen since the beginning
 Compatible with vacuum
infrastructure
 Mature technique


Increase cavity finesse (~900)
Enlarged spot size on test
masses
 From 2/5 cm to 5/6 cm

Use DC detection
 New higher finesse output mode
cleaner
 Under vacuum photodiodes
Marcel Grossman 12, Paris, July 13th 2009
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Non degenerate cavities/
Multiple payloads

Main drivers
 Reduce signal loss due to scattering into higher modes
 Improve interferometer control signals
 Relax spec on thermal compensation system

Use non degenerate recycling cavities
 Cavity length ~ 28 m
 Telescope in the recycling cavity
 Reduce beam size on input/output bench (~ from cm’s
to mm’s)

Need for multiple payloads
 Impact on couplings and mirror position control
Marcel Grossman 12, Paris, July 13th 2009
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Laser

Main driver
 Reduce shot noise
 Improve high frequency sensitivity

Increase laser power 10x
 Reference solution: solid state amplifier
developed at LZH for Advanced LIGO (can
provide 180 W)
 Alternative: fiber laser

Drawbacks
 Radiation pressure noise
 Mirror thermal lensing

Mitigation
 Heavier mirrors
 Improved thermal compensation
Marcel Grossman 12, Paris, July 13th 2009
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Input optics

Main drivers
 Manage higher power, Meet AdV noise requirements

Input mode cleaner
 Keep 144 m suspended triangular cavity: more noise filtering, easier modulation frequency choice,
existing infrastructure
 Mirrors: heavier for radiation pressure mitigation, improved polishing for smaller low angle scattering

Electro-optics modulators
 Low thermal lensing KTP crystals

Faraday isolator
 Realized at IAP (Russia), meets AdV specs
Marcel Grossman 12, Paris, July 13th 2009
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Thermal compensation

Main driver
 Avoid degradation of interferometer performance
due to thermal lensing

Main effects
Shielded heating rings will
compensate HR surface
deformations
 Wavefront distortion in PR/SR cavities
 Test masses surface deformation

Thermal compensation
 Combined action of a CO2 laser and heating
rings
 CO2 laser cannot act directly on test masses
» Requirements on power stabilization too demanding
 Project CO2 laser on silica compensation plates

Drawback
 Additional transmissive optics on the main beam

Mitigation
 CP seismically isolated
 Wedge on CP
 Tilted to suppress impact on alignment signals
Marcel Grossman 12, Paris, July 13th 2009
Compensation plates shined with
CO2 laser will correct thermal
effects in the PRC
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Mirrors

Main drivers
 Thermal noise reduction
 Radiation pressure noise mitigation
 Scattering losses reduction

Use state of the art coating in 2011
 Ti:Ta2O5 reference solution
 On going R&D

Larger mass
 35 cm diameter, 20 cm thick
 42 kg


Low absorption fused silica
Scattering loss reduction
 Specs: flatness < 1 nm, Roughness < 1 Ǻ
 Reference solution: corrective coating
 Alternative: improved polishing
Marcel Grossman 12, Paris, July 13th 2009
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Seismic isolation

Main drivers
 Isolate test mass form seismic noise
 Control mirror positions

Use present Virgo super-attenuators (SA)
 Compliant with AdVirgo requirements


A new SA to be built for the signal recycling mirror
More isolation required for input and output optics
 Due to use of non-degenerate recycling cavities

Upgrade of top stage control
 Full 6 dof control; add tilt control
 Help control in windy days
 Foreseen since the beginning
Marcel Grossman 12, Paris, July 13th 2009
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Monolithic suspensions

Main driver
 Reduction of suspensions thermal noise


Use of fused silica fibers to suspend the test masses
Relevant progress during the last months
 Fiber production
» Geometry under control
» Excellent reproducibility
 Clamp design
 Welding technique
» Can be done far from the mirror
 Assembly procedure thoroughly tested
 Dummy monolithic suspension tested
Marcel Grossman 12, Paris, July 13th 2009
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Vacuum envelope

Main driver
 Reduction of index of refraction fluctuation noise

Reduce residual pressure in the Virgo tubes
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Current pressure ~ 10-7 mbar (dominated by water)
Reduction 100x required
Tubes bakeout needed
Need to separate tubes from towers
Design solution
 Cryotraps at the tubes extremes
Marcel Grossman 12, Paris, July 13th 2009
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Infrastructure: ‘culture’ noise reduction

Main driver
 Reduce machine noise

Virgo commissioning experience showed that infrastructure improvements
allows reducing environmental noise
 Replacement of old air conditioning machines and relocation out of experimental halls
 Insulated rooms for noisy racks, power supplies, scroll pumps
 Improvement of laser/detection acoustic isolation
Marcel Grossman 12, Paris, July 13th 2009
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Advanced Virgo performance
Marcel Grossman 12, Paris, July 13th 2009
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Risk reduction: Virgo+

The Virgo+ program is helping reducing the AdV risk by
tackling in advance some relevant issues:
 Higher power laser
 Use of TCS
 Monolithic suspensions
 Higher arm cavity finesse

The use of monolithic suspensions in Virgo+ is crucial to
reduce the risks connected to the fused silica fibers
Marcel Grossman 12, Paris, July 13th 2009
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Timeline
150
AdV goal
AdV Science Run 1
Advanced Virgo commissioning
Advanced Virgo installation
8
Installation of new mirrors and monolithic suspensions
6.5
Virgo Science Run 2
Virgo+ commissioning
Virgo+ installation
Marcel Grossman 12, Paris, July 13th 2009
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Status of the project and conclusions


Advanced Virgo baseline design and cost evaluation is completed
Project reviewed by an External Review Committee (ERC, chair B. Barish)
 Review started in Nov 08 and concluded in May 09
 Final report submitted to the EGO council (funding agencies)
 The ERC supports Advanced Virgo as a worthwhile investment for funding

INFN set up a scientific committee (chair N. Cabibbo) to set priorities
among the new proposed experiments
 Advanced Virgo was top ranked

EGO council meeting on July the 2nd

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Virgo/EGO are allowed to place the first preparatory orders
Project leader is appointed
Final INFN decision expected at the end of July
Extraordinary EGO council meeting called on October the 6th for final decision
Advanced Virgo is ready to go and join the 2nd generation GW detector
network in 2015
Marcel Grossman 12, Paris, July 13th 2009
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