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Thermal Compensation NSF
David Ottaway
LIGO Laboratory
MIT
Advanced LIGO Technical Review G020467-00-R
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Overview1. Labs and people
2. Adaptive thermal compensation overview and current conceptual design
3. Thermal loading effects on Advanced LIGO
4. Road map for design choices (Set by other systems)
5. Summary of current results from subscale tests and modeling
6. Current issues
7. Plans and Resources Required
Advanced LIGO Technical Review G020467-00-R
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People and Labs
LIGO MIT Dave Ottaway, Ken Mason, Mike Zucker and Ryan Lawrence
LIGO Caltech Bill Kells, Erika de Ambrosia and Phil WillemsStanford Ray Beausoleil (Melody development)
UWA* David Blair, Bram Slagmolen and Jerome Degallaix
ANU* David McClellandUA* 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
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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
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Conceptual Design
PRM
SRM
ITM
ITM
Compensation Plates
•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)
Advanced LIGO Technical Review G020467-00-R
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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
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Thermal Comparison of Advanced LIGO to LIGO 1
Parameter LIGO ILIGO II
SapphireLIGO IISilica
Units
Input Power 6 125 80 W
PRC
Power0.4 2.1 1.3 kW
Arm Cavity Power
26 850 530 kW
Substrate Absorption
5 10-40 (30) 0.5-1 (0.5) ppm/cm
Coating
Absorption0.5
0.1-0.5(0.5)
0.1-0.5 (0.5)
ppm
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Effect on Advanced LIGO Interferometers (Melody Prediction)
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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
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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
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Thermophysical Parameters Measurement (295-320 K)
Sapphire (C and A axes)
Parameter Value Error Units
dn/dT 7.2 0.5 ppm/K
a 5.1 0.2 ppm/K
c 5.6 0.2 ppm/K
ka 36.0 0.5 W/m/K
kc 39.0 0.5 W/m/K
Fused Silica (Corning 7940)
Parameter Value Error Units
dn/dT 8.7 0.3 ppm/K
0.55 0.02 ppm/K
kth 1.44 0.02 W/m/K
Advanced LIGO Technical Review G020467-00-R
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Heater Ring Thermal Compensation
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Thermal Compensation of Point Absorbers in Sapphire
Advanced LIGO Technical Review G020467-00-R
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Sub Scale Scanning Laser Test
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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
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Predicted Effected of Thermal Compensation on Advanced LIGO
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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
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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
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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
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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