Plans for Advanced Virgo

1. Plans for Advanced Virgo Raffaele Flaminio LMA/CNRS on behalf of the Virgo Collaboration SUMMARY - Motivations - Detector design - Expected sensitivity - Status and timeline

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)

3. Virgo noise budget Actuation Eddy currents Magnetic Scattered light • Noise budget well understood • Sensitivity close to fundamental noises • Large improvements need large hardware modifications: Advanced Virgo Suspension thermal SHOT Mirror thermal

4. Enhanced LIGO/Virgo+ Virgo/LIGO 108 ly Adv. Virgo/Adv. LIGO Credit: R.Powell, B.Berger 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 generationdetector • 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

5. 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

6. Advanced Virgo design

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

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

9. 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

10. 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

11. Thermal compensation Shielded heating rings will compensate HR surface deformations • Main driver • 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 Compensation plates shined with CO2 laser will correct thermal effects in the PRC

12. 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

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

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

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

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

17. Advanced Virgo performance

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

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