thermal compensation system for virgo+

Alessio RocchiINFN Roma Tor Vergata

Thermal Compensation System for Virgo+

A. Rocchi - 24.10.2007 LSC-Virgo Meeting

Thermal Lensing

• Observed in Virgo through reduction of the sidebands gain.


0 2000 4000 6000 8000 1 104 1.2 104 1.4 104 1.6 104 1.8 104 2 104 2.2 104 2.4 1040

0.005

0.01

0.015

0.02

0.0250.021

0

wi t1( )

ni t2( )

WI ta( )

NI ta( )

256000 t1 t2 ta

ITMs absorptions evaluated through coupled thermal-modal FEM with Ansys

Red and blue curves experimental frequency shifts

WI (7.8±1.1) ppm NI (2.3±0.3) ppm

ITMs effective absorptions

0 2000 4000 6000 8000 1 104 1.2 104 1.4 104 1.6 104 1.8 104 2 104 2.2 104 2.4 1040

0.005

0.01

0.015

0.02

0.0250.021

1.719 106

wi t1( )

ni t2( )

256000 t1 t2 ta

WI

NI

green and pink FEM results

Errors come from dependency of the model from uncertainty on elastic parameters dependency on temperature

Time span ~25000sec

f (

Hz)

New measurement by M. Punturo, NI absorption ~ 4.5

ppm

0.025

0


Thermal lensing evaluation

-350

-300

-250

-200

-150

-100

-50

0

50

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16

P=7W, Grec=40, F=50, Abs=7.7ppmP=7W, Grec=40, F=50, Abs=1.25ppmP=25W, Grec=19, F=150, Abs=1.25ppmP=25W, Grec=35, F=150, Abs=1.25ppmP=25W, Grec=40, F=50, Abs=1.25ppmP=25W, Grec=40, F=50, Abs=7.7ppm

OP

D (

nm)

Radial Distance (m)

Beausoleil analitycal solution


Thermal Compensation System

• TCS for Virgo+: annular heating of ITMs with dc CO2 laser• “Annular” profile

– from simulations: reasonable parameters to compensate inner radius~2.5 cm, outer radius~11÷14 cm

Desirable properties:• It is easily adaptable as new understanding of the ITF is realized• It does not require a significant vacuum incursion to install as this would

lead to significant down time to the instrument

Two phases installation:1. Feb 2008, system without power stabilization control loop2. May-June 2008, installation of the power stabilization control loop


TCS Power requirements

Virgo on WI mirror (absorption 7.7ppm) ~1.8 W

Virgo (nominal absorption) ~0.4 W

Virgo on WI mirror (absorption 7.7ppm, Plas=25W) ~6.2 W

Virgo (nominal absorption, Plas=25W) ~1.3 W

Virgo+, (F=150, Grec=19) (nominal absorption) ~1.5 W

Virgo+ (F=150, Grec=35) (nominal absorption) ~2.8 W


Optical layout


TCS optical bench

Oven

Optical benches positioning

Acoustic enclosure

WI tower

NI tower


Final design of the Optical Imaging System

P. La Penna & E. Genin

250

mm

100% efficiency

Single axicon to get the “annular” profile


Two large in-vacuumsteering mirrors (=190mm)

Positioning controlled manually in all DOFs

Remotely controlled via steppingmotors in angular DOFs and onetranslation

UHV ZnSe viewportDN100CFClear aperture 90mm


CO2 Laser AOM

Beam Dump

Schematic view

Beam Dump

Power Meter

L1 L2

L3

L4

L5

AXICON

/2waveplate Polarizer

Components in the blue box are used for laser power stabilization, will be installed by mid 2008

To in-vacumm steering mirror

Aiming LaserLX

Laser output power control


Tests in Tor Vergata Labs before installation on Virgo

• Measure the RIN of the laser– So we can have an estimate of the injected noise in

the first phase installation

• Check the efficiency of the Optical Imaging System


Preliminary designof the first in-vacuum mirror

Material: Aluminum

T. Zelenova

~80

0mm


Exploring different designs for the in-vacuum optics holders, with T. Zelenova

226Hz

252Hz

537Hz


f0=537Hz

Unloaded

Loaded with mirror (2kg)

f0=375Hz


Error signal generation• E. Calloni & M. Laval demonstrated that Phase camera 0 + DarkF tools to

“measure” TCS • Pine-hole photodiodes error signal generation• Phase camera 1 an upgraded tool to understand sidebands and TCS

B5

P1

P2

Pin-hole mirror

Photodiodes

Signal = P1-P2

This is only one error signal, but two are needed. Investigating the possibility to use the signal from B2


CO2 laser power stabilization

20W CO2 Laser

AOMPD

PD

Critical components

*DP

AreaRIN

inc

New LASY-20S from Access Laser Co, pre-stabilized, temperature tuned (no line hops)


Evaluation of TCS noise injected in Virgo+, if RIN is stabilized @ 3×10-7/√Hz, flat over the frequency range 10 Hz to 1000 Hz, TCS power=1.5W.

Noise budget

10 100 1 1031 10 24

1 10 23

1 10 22

1 10 21

1 1021

1024

ztot ( )

z1 ( )

z ( )

zrad ( )

Sh2 fv2( )

Sh fv( )

100010 fv2 fv

Virgo+ sensitivity (without monolithic suspensions)Virgo+ sensitivity (with monolithic suspensions)TotalFlexuralThermoelastic+ThermorefractiveRadiation pressure


Building and validating the FE model

Comparison with analytical solutionBeausoleil (LIGO-P020026-00-D)

0

0,1

0,2

0,3

0,4

0,5

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16

Analytical Solution (Beausoleil)Ansys - surf151

Tem

pera

ture

(K

)

Radial distance (m)

Max difference ~ 0.3%

Difference is 0.55Hzless than 0.01%

• DRUM MODE

• ANSYS FEM f= 5584.15 Hz

• Experimental value f= 5584.7 Hz

http://www.ligo.caltech.edu/docs/P/P020026-00.pdf


Possible optical layout

AXICON

thermal compensation system for virgo+

Documents