1. Advanced LIGO Suspension Status Caroline A. Cantley Advanced LIGO Suspension Team / University of Glasgow for the GEO600 Group LSC Meeting, LLO March 2004 LIGO-G040054-01-K

2. 2 Overview Triple/quad development update Eddy current damping update OSEM development Optic ear development CO 2 laser pulling & welding of fibres Violin and pendulum Q measurements update Future work

3. LIGO-G040054-01-K 3 Advanced LIGO suspension team LIGO Lab : CIT: H. Armandula, M. Barton, D. Coyne, J. Heefner, J. Romie, C. Torrie, P. Willems. MIT: P. Fritschel, R. Mittleman, D.Shoemaker LHO: B. Bland, D. Cook LLO: J. Hanson, H. Overmier, G. Traylor GEO600: Glasgow: G. Cagnoli, C. Cantley, D. Crooks, E. Elliffe, A. Grant, A. Heptonstall, J. Hough, R. Jones, M. Perreur-Lloyd, M. Plissi, D. Robertson, S. Rowan, K. Strain, P. Sneddon, H. Ward Universitat Hannover: S. Gossler, H. Lueck Stanford University : N. Robertson (also GEO/Glasgow) Rutherford Appleton Laboratory (CLRC): J. Greenhalgh, I. Wilmut University of Birmingham: S. Aston, D. Hoyland, C. Speake, A. Vecchio, M. Cruise Strathclyde University: N. Lockerbie

4. LIGO-G040054-01-K 4 Triple/quad development update MC controls prototype install LASTI Jun ’04 Quad controls prototype CIT Nov ’04; LASTI Feb ‘05 Focused on quad design since Jan ’04 pendulum modelling FEA of structure (150Hz requirement) mass budget for structure 140kg + 25%; currently 170kg Other CIT prototypes single stage 40 kg with 4 x 4 ECD array double stage 40 kg + 40 kg blade ECD tested on upper MC blade 2 x 2 ECD array tested on MC triple and single suspension (talks by N. Robertson, J. Romie & C. Torrie) RAL blade test facility (talks by J. Greenhalgh & I. Wilmut) Quad structure 1st mode 120 Hz GEO mass catcher RAL blade test facility (CIT, Glasgow, Stanford, RAL)

5. LIGO-G040054-01-K 5 Eddy current damping update Developed as low noise alternative to active damping systems Triple pendulum tests (Glasgow/CIT) Damping at top mass (modes coupled) NdFeB magnet arrays & Cu blocks Damping constant measured to be b ~ 26 kg/s for 4 x 4 array (greater than initial experiments suggested) Alternative/supplement for triples and some d.o.f.’s quads (vertical and roll) (talk by M. Plissi) (Plissi, Robertson, Torrie, Barton, Grant, Cantley, Strain, Willems, Romie, Skeldon, Perreur-Lloyd, Jones, Hough) Lightweight ‘clover-leaf’ design MATLAB model for b~26 kg/s undamped GEO style triple – longitudinal TF experimental

6. LIGO-G040054-01-K 6 OSEM development Basic shadow sensor sensitivity ~ 1 x 10 -10 m/  Hz at 10 Hz; range 3 mm (ptp) Not good enough for all suspensions / d.o.f.’s Geometric sensors developed to 1.5 x 10 -11 m/  Hz (but only at null); range 2 mm (ptp) Interferometric OSEM sensitivity 5 x 10 -13 m/  Hz; range 3 mm (ptp) UK recommend interferometric OSEMs where high sensitivity required (e.g. MC long. local) + basic shadow sensors (talk by S. Aston) Document issued for formal LIGO review in April (Aston, Cantley, Greenhalgh, Hoyland, Lockerbie, Robertson, Speake, Strain, Vecchio, Ward) Schematic of interferometric OSEM Laser Diode and collimation optics Adjustable mirror Susp. Mirror Cat’s Eye Attenuator and aperture Polariser Quarter-wave plate Non-polarising beam-splitter 70mm Polarising beam-splitterHalf-wave plate mirror A BC D E FG Pd2Pd1Pd3 40mm

7. LIGO-G040054-01-K 7 Optic ear development – design criteria Develop GEO design to allow suspension of heavier Advanced LIGO masses 10 kg  40 kg Design drivers achieve required mechanical strength bond thermal noise suspension thermal noise Ear geometry/position ribbon/wire flexure point offsets minimise peeling effect Try to maintain stress level in bond bond area scaled up with mass GEO 3 cm 2  Adv.LIGO 12 cm 2 per ear (cont’d) (Cagnoli, Cantley, Crooks, Elliffe, Hough, Rowan) Advanced LIGO ‘Mark I’ ear design wire breakoffs ribbon breakoff Stress contours in GEO ear under load

8. LIGO-G040054-01-K 8 Optic ear development – thermal noise Ear bond thermal noise should be less than 10% of target strain sensitivity at 100 Hz h(f ) ~ 3 x 10 -24 /  Hz 12 cm 2 per ear gives 17% This could set limit on ear area scaling GEO 3 cm 2  Adv.LIGO 4.2 cm 2 per ear design against peeling effect FE analysis of loaded ear (max. stress) ear strength testing (talk by E. Elliffe) Needs further discussion (Cagnoli, Cantley, Crooks, Elliffe, Hough, Rowan) But need to consider the inhomogeneous thermal noise associated with ear attachment Quantify by FE modelling of bond geometry FE model for inhomogeneous thermal noise prediction

9. LIGO-G040054-01-K 9 Non-uniformities in ribbon profile increased noise couplings degraded suspension performance Contamination premature breakage Advanced detectors require higher specification fibres Laser heating high precision heat delivery improved shape control reduced contaminants & defects spatially selective annealing  reduced stress  increased strength/reliability Develop machine to interface with mass catcher/assembly jig R&D funded in part from EGO CO 2 laser pulling & welding of fibres (Cagnoli, Cantley, Crooks, Jones, Hough, Bogenstahl, Perreur-Lloyd) Welding of 3mm silica rod using 9W CO2 laser Preliminary ribbon welding concepts GEO type ear H-piece ribbon Ear ‘I’ ribbon mirror galvo

10. LIGO-G040054-01-K 10 Violin and pendulum Q Investigations of relationship between fundamental material Q, violin mode Q and pendulum Q Violin Q experiment 2.4 kg mass single ribbon 420 x 1.12 x 0.12mm fundamental violin mode 324 Hz measured Q = 1.4 x 10 8 theoretical Q = 7 x 10 8 investigate difference High Q pendulum experiment 43.5 g mass single ribbon 405 x 1.2 x 0.11mm measured Q = 1.4 x 10 8 theoretical Q = 2.2 x 10 8 (mostly material loss & thermoelastic loss) 445 g pendulum (x 10 higher mass) limited by recoil loss Ongoing work on mitigation of test mass charging (talk by E. Elliffe) (Heptonstall, Cagnoli, Strain, Hough, Rowan, Elliffe) Violin mode Q experiment

11. LIGO-G040054-01-K 11 Future work Continue development of quad controls prototypes for LASTI & CIT Demonstrate assembly and eddy current damping on quad prototype at CIT LIGO formal OSEM review April 2004 Prototype optic ear to be designed and tested Development of CO 2 laser pulling & welding machine Continue investigations on relationship between fundamental material Q, violin mode Q and pendulum Q Start development of active damping system for violin modes Continue investigations on mitigation of charging effects