Michele Punturo WP3 meeting, Cascina 9-July-2004 Low frequency noises in GW ITF: R&D activities in VIRGO on Thermal noise reduction Michele Punturo WP3 meeting, Cascina 9-July-2004

Virgo Expected Sensitivity Curve

Virgo under commissioning C4 sensitivity (no PR) dominated by technical noises

Low frequency fundamental Noises Seismic Noise Newtonian Noise Thermal Noise Suspension Mirror Radiation pressure noise

Virgo SuperAttenuator Multi-pendulum (6) seismic filter + IP Cantilever blades for vertical seism attenuation Active controls to damp the resonant modes Seismic noise lower than expected thermal already @4Hz

Thermal noise in Virgo In Virgo the suspension thermal noise is expected to be dominant in the 4-40Hz range The mirror thermal noise “could be” dominant in the 40-300Hz In an advanced version of the detector, with at least 100W power laser, the thermal noise will be the largest enemy up to 500Hz

Current design Currently the Virgo mirrors are suspended by a system of two steel wires: C85 Steel selected to minimize the loss angle ant the creep effect Special clamps to reduce the clamping losses Lateral spacers to reduce the pendulum and mirror Q degradation

Silicate Bonding In each mirror are attached camera targets, frontal and lateral magnets and lateral spacers Silicate bonding technique has bee adopted to reduce the mirror Q degradation

Current performances A pendulum Q of ~106 is expected for Virgo We cannot measure it directly Pendulum thermal noise limit is still far from our sensitivity Read-Out mirror Q between 3×105 and 1.6×106 Effective loss angle computed through FEM of the dissipations in the mirror Perfect coincidence with the expected sensitivity curve

Mirror vibration in C4 data Input Mirrors Mirror vibration in C4 data End mirrors

R&D on Thermal noises “Historical” R&D activity on fused silica suspension Scientific targets reached few years ago Production of SiO2 fibers through H2-O2 flames Silicate bonding process under control 21 kg mirror suspended Engineering procedures to be defined: Complex SA: safety of the suspension Heavy mirror Transport Cleanliness issues R&D financed by EGO to Glasgow on fiber production with a CO2 laser

Intermediate term R&D Suspension fibers in mono-crystalline material Silicon is a good candidate both for a room temperature ITF and for a cryogenic 3rd generation detector Low intrinsic loss angle (10-8 – 10-10) High thermal conductivity at low temperature Zero thermal expansion coefficient at some “magic” temperatures Contribution at room temperature Thermo-elastic

Si thermal properties vs Temperature a(T): C.A. Swenson, J. Phys. Chem. Ref. Data, vo. 12(2), k(T) Thermophysical Properties of Matter, v1, Y.S. Touloukian, R.W. Powell, C.Y. Ho & P.G. Klemens, 1970, IFI/Plenum, NY

Production of Mono-Crystalline fibers A small furnace is available in the Pisa Labs (M.Tonelli) A larger one soon available (mPull down technology)

Expected sensitivity

Local Cooling Pcool(l)= Pabs(l)(l-lF)/lF We can used a traditional cold finger or a more advanced (and difficult) anti-stokes fluorescence mechanism It needs the doping of the crystalline fiber with rare earth impurities Possibility to cool down a localized region (flexural point in suspension fibers) R. I. Epstein et al. NATURE 377 (1995) Pcool(l)= Pabs(l)(l-lF)/lF

Optical cooling Low efficiency energy extraction TIR Possibility to increase the efficiency through a multi-pass technique using Total Internal Reflection in a fiber YAG:Er fiber f  800 mm

Cryogenic ITF Cryogenic Facility at the VIRGO-EGO site financed by EGO Cryostat (pulsed tubes) R&D financed by INFN at Rome Cryogenic payload R&D supported by INFN, STREGA and EGO

Cryogenic Payload Executive design of the prototype ready The request of offer to the company will be submitted next week To be mounted in the cryogenic facility in Cascina to test thermal and control issues

Radiation Pressure R&D In the 3rd generation ITF a power of 1-10MW could be stored in the FP cavities to reduce the shot noise Thermal noise could be reduced through a cryogenic approach Radiation pressure becomes a dominant noise at low frequency

Radiation pressure noise

New Idea Courty et al., [Phys. Rev. Lett. 90, 083601 (2003)] It is possible to reduce the radiation pressure noise in the frequency range of interest coupling the ITF cavity with an auxiliary control cavity

Coupling of the cavities Experimental and theoretical studies in progress: Effect of the others noise sources on the quantum locking Locking schemes and total number of cavities Experimental tests supported by INFN (Perugia) and EGO (LKB) Optical read-out noise cavity 1 free Optical read-out noise Cavity # 2 Optical read-out noise caviity 1 with feedback

Possible reduction of R.P.