1. 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

2. 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

3. Virgo noise budget Noise budget well understood
Actuation
Eddy currents
Magnetic
Scattered light
Suspension thermal
SHOT
Mirror thermal
Noise budget well understood
Sensitivity close to fundamental noises
Large improvements need large hardware modifications: Advanced Virgo
Marcel Grossman 12, Paris, July 13th 2009

4. 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
Need to improve the sensitivity
Upgrade Virgo to a 2nd generation detector
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
108 ly
Enhanced LIGO/Virgo+
Virgo/LIGO
Credit: R.Powell, B.Berger
Adv. Virgo/Adv. LIGO
Marcel Grossman 12, Paris, July 13th 2009

5. Advanced Virgo Science Case
1 day of AdVirgo data ~ 3 years of Virgo data
Coalescing binaries detection rates
BNS ~ 10/yr
BBH ~ /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

6. Advanced Virgo design
Marcel Grossman 12, Paris, July 13th 2009

7. 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

8. 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

9. Laser Main driver Increase laser power 10x Drawbacks Mitigation
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

10. Input optics Main drivers Input mode cleaner Electro-optics modulators
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

11. Thermal compensation Main driver Main effects Thermal compensation
Avoid degradation of interferometer performance due to thermal lensing
Main effects
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
Shielded heating rings will compensate HR surface deformations
Compensation plates shined with CO2 laser will correct thermal effects in the PRC
Marcel Grossman 12, Paris, July 13th 2009

12. Mirrors Main drivers Use state of the art coating in 2011 Larger mass
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

13. 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

14. 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

15. Vacuum envelope Main driver
Reduction of index of refraction fluctuation noise
Reduce residual pressure in the Virgo tubes
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

16. 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

17. Advanced Virgo performance
Marcel Grossman 12, Paris, July 13th 2009

18. 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

19. BNS INSPIRAL RANGE (Mpc)
Timeline
150
AdV goal
AdV Science Run 1
Advanced Virgo
Advanced Virgo commissioning
BNS INSPIRAL RANGE (Mpc) 08 09 10 11 12 13 14 15 16
Advanced Virgo installation
Virgo Science Run 2 8
Virgo+
Installation of new mirrors and monolithic suspensions
6.5
Virgo+ commissioning
Marcel Grossman 12, Paris, July 13th 2009
Virgo+ installation

20. 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
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