tcs update
DESCRIPTION
TCS update. INFN Roma Tor Vergata. Thermal Lensing Effects in Advanced Virgo. The cavity becomes less concentric, and the spot sizes at the mirrors will shrink (increase of thermal noise and reduction of arm cavity coupling to the input beam) - PowerPoint PPT PresentationTRANSCRIPT
TCS update
INFN Roma Tor Vergata
Advanced Virgo Meeting - 16.07.08 2
Thermal Lensing Effects in Advanced Virgo• Thermal compensation for Advanced Virgo, must take into
account the much greater circulating laser power (~800kW) • In Advanced Virgo, thermal effects will create distortions both
in the recycling and in the Fabry-Perot cavity:– Wavefront distortion in the PRC– HR surface elastic deformation
•The cavity becomes less concentric, and the spot sizes at the mirrors will shrink (increase of thermal noise and reduction of arm cavity coupling to the input beam)•Necessity to control the radii of curvature of all test masses, TCS will have to act on both ITM and ETM.
From S.Chelkowski presentation at 1.7.08 beweekly meeting
Advanced Virgo Meeting - 16.07.08 3
Advanced LIGO and Advanced Virgo share the same thermal issues. A possible TC System has already been proposed in the LIGO Collaboration
Red dots: shielded heating ringGreen rays: CO2 heating beamsBlue rays: sensing beams
Compensation plates will correct thermal effects in the PRCShielded heating rings will compensate HR surface deformationsHartmann sensors will be used to monitor TM and CP phase profile
Advanced LIGO TCS scheme
In the case of Advanced Virgo,The positioning of CPs in the PRC is a delicate issue due to its strong impact with the suspension systems
Advanced Virgo Meeting - 16.07.08 4
Simulation of thermal effects in Advanced Virgo Test Masses
In the simulation we used the following parameters:• 125W of input ITF power, beam radius on TM = 6 cm• FP cavity Finesse=885• gain of the SRC=23.5• absorptions of the coating and substrate respectively 0.5ppm
and 2ppm/cm• Total absorbed YAG power ~0.5W• Test Mass diameter: 350 mm• Test Mass thickness: 200 mm• Test Mass ROC (cold): 1530 m
Advanced Virgo Meeting - 16.07.08 5
Simulation of thermal effects in Advanced Virgo Test Masses
Effect of the Yag on ITM
Advanced Virgo Meeting - 16.07.08 6
Simulation of thermal effects in Advanced Virgo Test Masses
Effect of the Yag on ITM- Thermoelastic deformation
Thermo-elastic deformation of the HR surface
Change in the ROC
Advanced Virgo Meeting - 16.07.08 7
Simulation of thermal effects in Advanced Virgo Test Masses
Effect of the Yag on ITM- Lensing effect (thermooptic 95% + thermoelastic 5%)
Optical path length increase in the substrate.The focal length of the equivalent lens is 4.5 km
Advanced Virgo Meeting - 16.07.08 8
Simulation of thermal effects in Advanced Virgo Test Masses
Optical path length for different CO2 powers
Is it possible to correct both effects acting with a CO2 beam on the HR face of the ITM?
- heating profile due to AXICON- internal radius = 6 cm- external radius = 16 cm } Not optimized
Advanced Virgo Meeting - 16.07.08 9
Simulation of thermal effects in Advanced Virgo Test Masses
Temperature map for 9.7W of CO2
Is it possible to correct both effect acting with a CO2 beam on the HR face of the ITM?
- heating profile due to AXICON- internal radius = 6 cm- external radius = 16 cm } Not optimized
HR face displacement for 9.7W of CO2
Advanced Virgo Meeting - 16.07.08 10
Simulation of thermal effects in Advanced Virgo Test Masses
ROC for different CO2 powers
ROC=1530 m
ROC=1538 m
ROC=1556 m
ROC=1567 m
Is it possible to correct both effect acting with a CO2 beam on the HR face of the ITM?
- heating profile due to AXICON- internal radius = 6 cm- external radius = 16 cm } Not optimized
Advanced Virgo Meeting - 16.07.08 11
Since the ROC increases when heating the HR face, we tried acting with a CO2 beam on the AR face of the ITM. Same profile as HR heating.
Simulation of thermal effects in Advanced Virgo Test Masses
ROC=1530 m
ROC=1538 m
ROC=1518 m
The lensing effect is corrected at (almost) the same level as when acting on the HR face.What about the radius of curvature?
ROC for different CO2 powers
Advanced Virgo Meeting - 16.07.08 12
From the simulations it follows:
Simulation of thermal effects in Advanced Virgo Test Masses
•Front heating increases ROC (~3.1 m·W)
•Back heating decreases ROC (~2 m·W)
Need to find the correct balance between front and back heating
Advanced Virgo Meeting - 16.07.08 13
Starting from these evaluations we heated the TM on both faces, with the same profile, but different powers: 2.5 W on the HR face, 7.5 W on the AR face.
Simulation of thermal effects in Advanced Virgo Test Masses
Effect on the ROC
CO2 heating on both faces
Advanced Virgo Meeting - 16.07.08 14
Simulation of thermal effects in Advanced Virgo Test Masses
Effect on the OPL
CO2 heating on both faces
Temperature map
OPL
Advanced Virgo Meeting - 16.07.08 15LIGO Laboratory 15
TCS Noise Coupling Mechanisms• Thermoelastic (TE)- fluctuations in locally
deposited heat cause fluctuations in local thermal expansion
• Thermorefractive (TR)- fluctuations in locally deposited heat cause fluctuations in local refractive index
• Flexure (F)- fluctuations in locally deposited heat cause fluctuations in global shape of optic
Advanced Virgo Meeting - 16.07.08 1616
Flexure Noise- A Simple Model
probe beam
heating
heating
slat mirror
CM lineA very skinny mirror with ‘annular’ heating
The probe beam sees the mirror move at the center due to wiggling far from center
Advanced Virgo Meeting - 16.07.08 17
Ad Virgo TCS noise
17
Heating profile from Zemax fitted with:
W/m2
w1=0.099 and w2=0.0048
Zemax profileFit
This profile has been fed to a structural simulation in COMSOL to calculate thedisplacement of the HR face wrt the CM
Evaluation of the flexural noise
H(r) 64 10 5 r2
w12w2
4w2
2 r2 2e
2r 2
w12
0 0.05 0.1 0.15 0.20
5
10
15
20
Advanced Virgo Meeting - 16.07.08 18
Ad Virgo TCS noise
18
In case the CO2 is applied on the HR face,to have TCS noise 10 times smaller than AdVirgo sensitivity @ 50 Hz RIN must be 5·10-9 1/Hz
Flat RIN over the entire frequency band
No relevant change with TM 30 cm thick
In case of heating on both sides of the TM, the noise model must be reviewed to take into account possible cancellation mechanisms.
A cross check between the model with experimental data (Edwige from TCS commissioning) and analytical calculations (S. Ballmer) is in progress
10 100 1 103 1 10
41 10
26
1 1025
1 1024
1 1023
1 1022
1 1021
TCS noise totalFL noiseTR + TE noiseRad pressure noiseAdVirgo sensitivity
Advanced Virgo Meeting - 16.07.08 19
We started to investigate the behavior of heating ring, from a question done by Andreas:An interesting idea could be to optimize the ROC for a normal TEM00 modes then at a later stage use the TCS to change the ROC in order to adapt the cavities for higher order modes. Do you have any idea of how much static change we could get, say, from a ring heater without creating other problems? I am thinking of changing a ROC of maybe 1530m to 1600m or 1630m or so.
Simulation of thermal effects in Advanced Virgo Test Masses
Heating ring actuation
Geometry description: axisymmetric model
Model components: mirror with a cold ROC = 1530 m + ring heater placed in front of the HR face of the mirror at a distance of 5.5 cm.
Advanced Virgo Meeting - 16.07.08 20
Temperature distribution in the mirror (cold mirror at T= 295 K)
Simulation of thermal effects in Advanced Virgo Test Masses
Heating ring actuation
Displacement of the HR face
160 W delivered by the Heating ring. Temperature of the HR = 530 K
Advanced Virgo Meeting - 16.07.08 21
Simulation of thermal effects in Advanced Virgo Test Masses
Heating ring actuation
160 W delivered by the Heating ring. Temperature of the HR = 530 KDetailed calculations not yet performed (need to model the LG33 effect).Thermal lensing is probably overcorrected! This is possible only on ETM
Effect on the ROC
Advanced Virgo Meeting - 16.07.08 22
Next steps in simulations• Check of the noise model• Investigate the possibility to relax the RIN requirements with
both faces heating• Possibility to replace the CO2 beam on the back with a heating
ring• Evaluate the noise introduced by the heating ring• Study the case of HOLM:
– possibility to change statically the ROC to optimize it for the HOLM– determine the TCS requirements
• Determine the requirements of a possible CP• Study interaction of the TCS with nearby optics and hardware