1. Thermal Noise performance of advanced gravitational wave detector suspensions Alan Cumming, on behalf of the University of Glasgow Suspension Team 5 th April 2011

2. 2 Overview Silica suspension design for aLIGO Prototype aLIGO suspension Thermal noise performance and loss modelling Current status Future work

3. 3 aLIGO Monolithic Silica Stage Steel wires Penultimate mass ‘Ear’ Silica fibres End/input test mass ‘Ear’ Requirement: 10 -19 m/  Hz @ 10Hz Upper metal masses (22kg masses) Blade springs Lower Monolithic silica stage (40kg masses)

4. Prototype Suspension, MIT Laser pulled silica fibres 4 A. Heptonstall et al., Rev. Sci. Inst. 82, 011301 (2011) Fibres laser welded to ears Complete suspension

5. 5 Ear Fibre Neck Stock Weld Finite Element Analysis Use FEA to predict energy stored in the suspension elements and the dissipation dilution, D A. Cumming et al., Class. Quant. Grav., 215012, 2009, A. Cumming et al., Class. Quant. Grav., in preparation, 2011. Ear Horn

6. Modelling the suspension loss 6 Internal friction described by the mechanical loss  of the system For a suspension this originates from various different mechanisms in the fibre ends: Modelling with FEA gives Surface loss,  surf Bulk loss,  bulk Weld loss,  weld Thermoelastic loss,  th

7. 7 Modelling comparison with measured A. Cumming et al., Class. Quant. Grav., in preparation, 2011 Measurement of horizontal noise difficult Modelling compared by predicting loss of violin modes of suspension fibres Measured on MIT prototype suspension Gives good confidence in modelling technique Violin modeFEA Frequency (Hz) Measured Frequency (Hz) Projected loss from FEA modelMeasured loss Fundamental511511,5201.50 x 10 -9 1.61 x 10 -9 1 st harmonic101710201.75 x 10 -9 2.16 x 10 -9

8. 8 aLIGO Final Stage Noise (Single Test Mass) 10 -19 m/  Hz @ 10Hz A. Cumming et al., Class. Quant. Grav., in preparation, 2011

9. 99 Current status and future work Suspension design for aLIGO now finalised Preparation for the start of manufacture of production suspensions for first installations into the LIGO instruments is currently ongoing First installations timetabled for summer 2011 Studies already ongoing on methods to further increase sensitivity for enhancements to aLIGO using the FEA modelling techniques Application of modelling to future third generation detectors using different materials and possibly cooled to cryogenic temperatures

10. 10

11. 11 Thermal Noise Model Use the following loss terms to model the welds, ear horns and fibres A.M. Gretarsson et al., Phys. Rev. A, 2000 G. Cagnoli and P.A. Willems, Phys. Rev. B, 2002 P.A. Willems, T020003-00 M.Barton et al., T080091-00-K A. Heptonstall et al., Phys. Lett. A, 354, 2006 A. Heptonstall et al., Class. Quant. Grav, 035013, 2010