Thermal Compensation NSF David Ottaway LIGO Laboratory MIT

Advanced LIGO Technical Review G020467-00-R Overview Labs and people Adaptive thermal compensation overview and current conceptual design Thermal loading effects on Advanced LIGO Road map for design choices (Set by other systems) Summary of current results from subscale tests and modeling Current issues Plans and Resources Required Advanced LIGO Technical Review G020467-00-R

Advanced LIGO Technical Review G020467-00-R People and Labs LIGO MIT Dave Ottaway, Ken Mason, Mike Zucker and Ryan Lawrence LIGO Caltech Bill Kells, Erika de Ambrosia and Phil Willems Stanford Ray Beausoleil (Melody development) UWA* David Blair, Bram Slagmolen and Jerome Degallaix ANU* David McClelland UA* Peter Veitch, Jesper Munch and Aiden Brooks * Gin Gin Facility contributors and members of the Australian ACIGA collaboration Advanced LIGO Technical Review G020467-00-R

Adaptive Thermal Compensation Due to high circulation power, significant power will be absorbed in the test masses => Significant thermal distortions Absorption characteristics unlikely to be sufficiently accurately known to allow an Initial LIGO 1 Style Point design NEED Active Compensation of the mirrors This sub-system provides such a means of compensation Advanced LIGO Technical Review G020467-00-R

Advanced LIGO Technical Review G020467-00-R Conceptual Design Design utilizes a fused silica suspended compensation plate Actuation by a scanned CO2 laser (Small scale asymmetric correction) and nichrome heater ring (Large scale symmetric correction) No direct actuation on ITMs for improved noise reduction, simplicity and lower power (Sapphire) PRM SRM ITM Compensation Plates Advanced LIGO Technical Review G020467-00-R

Advanced LIGO Technical Review G020467-00-R Thermal Distortion Absorption in coatings and substrates => Temperature Gradients Temperature Gradients => Optical path distortions 3 Types of distortions, relative strengths of which are shown below: Sapphire Fused Silica Thermo-optic 1 26 Thermal Expansion 0.8 1.6 Elasto-optic Effect 0.2 - 0.3 Advanced LIGO Technical Review G020467-00-R

Thermal Comparison of Advanced LIGO to LIGO 1 Parameter LIGO I LIGO II Sapphire LIGO II Silica Units Input Power 6 125 80 W PRC Power 0.4 2.1 1.3 kW Arm Cavity Power 26 850 530 Substrate Absorption 5 10-40 (30) 0.5-1 (0.5) ppm/cm Coating Absorption 0.5 0.1-0.5(0.5) 0.1-0.5 (0.5) ppm Advanced LIGO Technical Review G020467-00-R

Effect on Advanced LIGO Interferometers (Melody Prediction) Advanced LIGO Technical Review G020467-00-R

Requirements that flow from other systems Core Optics (Down select) Sapphire -Significant possible inhomogeneous absorption -> Small spatial scale correction (scanning laser) -Large thermal conductivity -> Small amount of coarse compensation (ring heater) on compensation plates Fused Silica -Poor thermal conductivity and homogenous absorption (ring heater) DC or RF read out scheme (Down select) -Reduces dependence on sidebands, might affect design requirements Wavefront Sensing (LIGO 1 experience, not fully understood) -High spatial quality sidebands are probably necessary for accurate alignment control, may negate the effect of read out scheme Advanced LIGO Technical Review G020467-00-R

Summary of Subscale Experiments and Modeling Accurate measurements of fused silica and sapphire material properties Experimental demonstration of shielded heater ring coarse spatial correction Experimental demonstration of scanning CO2 laser fine spatial scale correction Accurate models of Advanced LIGO Interferometers style interferometer using Melody and finite element analysis (Femlab), (Thermal modeling without SRM) Scaling from subscale to full scale understood Work done by Ryan Lawrence Advanced LIGO Technical Review G020467-00-R

Thermophysical Parameters Measurement (295-320 K) Sapphire (C and A axes) Parameter Value Error Units dn/dT 7.2 0.5 ppm/K aa 5.1 0.2 ac 5.6 ka 36.0 W/m/K kc 39.0 Fused Silica (Corning 7940) Parameter Value Error Units dn/dT 8.7 0.3 ppm/K a 0.55 0.02 kth 1.44 W/m/K Advanced LIGO Technical Review G020467-00-R

Heater Ring Thermal Compensation Advanced LIGO Technical Review G020467-00-R

Thermal Compensation of Point Absorbers in Sapphire Advanced LIGO Technical Review G020467-00-R

Sub Scale Scanning Laser Test Advanced LIGO Technical Review G020467-00-R

Scanning Laser Test Result Uncorrected Optic (6712 ppm scatter from TEM00) Corrected Optic (789 ppm scattered from TEM00) Advanced LIGO Technical Review G020467-00-R

Predicted Effected of Thermal Compensation on Advanced LIGO Advanced LIGO Technical Review G020467-00-R

Advanced LIGO Technical Review G020467-00-R Current Issues Gravitational wave sideband distortion and its effect on sensitivity. Generated within the cavity no distortion nulling due to prompt reflection. Greater understanding through incorporation in through new improvements in Melody Experimental test to confirm Melody Fabry-Perot mode size change due to input test mass surface deformation => Spot size change (actuate on arm cavity faces) Accurate 2D absorption maps of Sapphire to aid in actuator selection (negative or positive dN/dT actuator plates) Development of full scale prototype Advanced LIGO Technical Review G020467-00-R

Research and Engineering Plans Set design requirements utilizing Melody Already started with the work of Ryan Lawrence Develop and test full scale prototype Performance measured using Shack-Hartmann sensor (LIGO) Diffraction limits do not allow full spatial test on bench-top Concurrently experimentally validate Melody Subscale high power tests in the Gin Gin Facility (ACIGA) Measurements from initial LIGO (LIGO) Develop alternative instrumentation strategies Alternative instrumentation strategy (Hartmann Sensor) (ACIGA) Multi-Pixel sensor (Phase Camera) preliminary experience gained at LIGO MIT (LIGO) Confirm final design Advanced LIGO Technical Review G020467-00-R

Advanced LIGO Technical Review G020467-00-R Schedule Oct 2002 Pre-Conceptual Design Review Oct 2003 Gin Gin commissioning begins 10 Feb 2004 Conceptual Design Review 01 Jun 2004 Gin Gin delivers first result 01 Dec 2004 Preliminary Design Review 05 Dec 2005 Gin Gin delivers final results 03 Jul 2006 Final Design Review Mid 2006 -2007 Fabrication and procurement Advanced LIGO Technical Review G020467-00-R

Advanced LIGO Technical Review G020467-00-R Summary of Costs Labor for development Scientist 5.8 FTE Years Engineer 4.2 FTE Years Grad Student 0.7 FTE Years Technician 2.7 FTE Years $669,789 Contract labor for manufacture Technician $336,510 Equipment for Lab Tests $145,000 Equipment for Installation $440,691 Total (Inc Overhead & Contingency) $3,054,886 Advanced LIGO Technical Review G020467-00-R