1. Thermal Compensation NSF
David Ottaway
LIGO Laboratory
MIT

2. 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 G R

3. 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 G R

4. 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 G R

5. 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 G R

6. 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 G R

7. 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
(0.5)
(0.5)
ppm
Advanced LIGO Technical Review G R

8. Effect on Advanced LIGO Interferometers (Melody Prediction)
Advanced LIGO Technical Review G R

9. 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 G R

10. 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 G R

11. 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 G R

12. Heater Ring Thermal Compensation
Advanced LIGO Technical Review G R

13. Thermal Compensation of Point Absorbers in Sapphire
Advanced LIGO Technical Review G R

14. Sub Scale Scanning Laser Test
Advanced LIGO Technical Review G R

15. Scanning Laser Test Result
Uncorrected Optic (6712 ppm scatter from TEM00) Corrected Optic (789 ppm scattered from TEM00)
Advanced LIGO Technical Review G R

16. Predicted Effected of Thermal Compensation on Advanced LIGO
Advanced LIGO Technical Review G R

17. 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 G R

18. 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 G R

19. 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
Fabrication and procurement
Advanced LIGO Technical Review G R

20. 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 G R