thermal compensation nsf david ottaway ligo laboratory mit

Thermal Compensation NSF

David Ottaway

LIGO Laboratory

MIT

Advanced LIGO Technical Review G020467-00-R

2

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


3

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


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


5

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)


6

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


7

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)


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


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


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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


12

Heater Ring Thermal Compensation


13

Thermal Compensation of Point Absorbers in Sapphire


14

Sub Scale Scanning Laser Test


15

Scanning Laser Test Result

Uncorrected Optic (6712 ppm scatter from TEM00) Corrected Optic (789 ppm scattered from TEM00)


16

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


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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


19

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


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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

thermal compensation nsf david ottaway ligo laboratory mit

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