Advanced LIGO Suspension Status Caroline A Cantley Advanced

Advanced LIGO Suspension Status Caroline A. Cantley Advanced LIGO Suspension Team / University of Glasgow for the GEO 600 Group LSC Meeting, LLO March 2004 LIGO-G 040054 -01 -K

Overview n n n n LIGO-G 040054 -01 -K 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 2

Advanced LIGO suspension team n 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 n GEO 600: 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 n Stanford University: N. Robertson (also GEO/Glasgow) n Rutherford Appleton Laboratory (CLRC): J. Greenhalgh, I. Wilmut n University of Birmingham: S. Aston, D. Hoyland, C. Speake, A. Vecchio, M. Cruise n Strathclyde University: N. Lockerbie LIGO-G 040054 -01 -K 3

Triple/quad development update n n n MC controls prototype install LASTI Jun ’ 04 Quad controls prototype CIT Nov ’ 04; LASTI Feb ‘ 05 Focused on quad design since Jan ’ 04 n n pendulum modelling FEA of structure (150 Hz requirement) mass budget for structure 140 kg + 25%; currently 170 kg Other CIT prototypes n n 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 Quad structure 1 st mode 120 Hz (talks by N. Robertson, J. Romie & C. Torrie) n RAL blade test facility (talks by J. Greenhalgh & I. Wilmut) (CIT, Glasgow, Stanford, RAL) LIGO-G 040054 -01 -K GEO mass catcher RAL blade test facility 4

Eddy current damping update n n n Developed as low noise alternative to active damping systems Triple pendulum tests (Glasgow/CIT) Damping at top mass (modes coupled) Nd. Fe. B magnet arrays & Cu blocks Damping constant measured to be b ~ 26 kg/s for 4 x 4 array (greater than initial experiments suggested) n Alternative/supplement for triples and some d. o. f. ’s quads (vertical and roll) GEO style triple – longitudinal TF experimental MATLAB model for b~26 kg/s undamped Lightweight ‘clover-leaf’ design (talk by M. Plissi) (Plissi, Robertson, Torrie, Barton, Grant, Cantley, Strain, Willems, Romie, Skeldon, Perreur-Lloyd, Jones, Hough) LIGO-G 040054 -01 -K 5

OSEM development n n n 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) n Document issued formal LIGO review in April 70 mm Adjustable mirror Attenuator and aperture D Laser Diode and collimation optics A 40 mm Pd 3 B G F Pd 1 Pd 2 C Cat’s Eye Polariser Quarter-wave plate Polarising beam-splitter Susp. Mirror E Non-polarising beam-splitter Half-wave plate mirror Schematic of interferometric OSEM (Aston, Cantley, Greenhalgh, Hoyland, Lockerbie, Robertson, Speake, Strain, Vecchio, Ward) LIGO-G 040054 -01 -K 6

Optic ear development – design criteria n n Develop GEO design to allow suspension of heavier Advanced LIGO masses 10 kg 40 kg Design drivers n n Ear geometry/position n achieve required mechanical strength bond thermal noise suspension thermal noise ribbon/wire flexure point offsets minimise peeling effect wire breakoffs ribbon breakoff Advanced LIGO ‘Mark I’ ear design Try to maintain stress level in bond area scaled up with mass GEO 3 cm 2 Adv. LIGO 12 cm 2 per ear (cont’d) n (Cagnoli, Cantley, Crooks, Elliffe, Hough, Rowan) LIGO-G 040054 -01 -K Stress contours in GEO ear under load 7

Optic ear development – thermal noise n n n But need to consider the inhomogeneous thermal noise associated with ear attachment Quantify by FE modelling of bond geometry 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 n FE analysis of loaded ear (max. stress) n ear strength testing (talk by E. Elliffe) n n Needs further discussion FE model for inhomogeneous thermal noise prediction (Cagnoli, Cantley, Crooks, Elliffe, Hough, Rowan) LIGO-G 040054 -01 -K 8

CO 2 laser pulling & welding of fibres n n n n n Ear ‘I’ premature breakage Advanced detectors require higher specification fibres Laser heating n n increased noise couplings degraded suspension performance Contamination n n GEO type ear Non-uniformities in ribbon profile 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 mirror galvo ribbon H-piece Preliminary ribbon welding concepts ribbon Welding of 3 mm silica rod using 9 W CO 2 laser (Cagnoli, Cantley, Crooks, Jones, Hough, Bogenstahl, Perreur-Lloyd) LIGO-G 040054 -01 -K 9

Violin and pendulum Q n n Investigations of relationship between fundamental material Q, violin mode Q and pendulum Q Violin Q experiment n n n 2. 4 kg mass single ribbon 420 x 1. 12 x 0. 12 mm fundamental violin mode 324 Hz measured Q = 1. 4 x 108 theoretical Q = 7 x 108 investigate difference n High Q pendulum experiment n 43. 5 g mass n single ribbon 405 x 1. 2 x 0. 11 mm n measured Q = 1. 4 x 108 Violin mode Q experiment n theoretical Q = 2. 2 x 108 (mostly material loss & thermoelastic loss) n 445 g pendulum (x 10 higher mass) limited by recoil loss Ongoing work on mitigation of test mass charging (talk by E. Elliffe) n (Heptonstall, Cagnoli, Strain, Hough, Rowan, Elliffe) LIGO-G 040054 -01 -K 10

Future work n n n n 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 LIGO-G 040054 -01 -K 11