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TCS update

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)

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TCS update

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  1. TCS update INFN Roma Tor Vergata

  2. 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) • 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 • 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

  3. Advanced LIGO and Advanced Virgo share the same thermal issues. A possible TC System has already been proposed in the LIGO Collaboration Advanced LIGO TCS scheme Compensation plates will correct thermal effects in the PRC Shielded heating rings will compensate HR surface deformations Hartmann sensors will be used to monitor TM and CP phase profile 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 Red dots: shielded heating ring Green rays: CO2 heating beams Blue rays: sensing beams 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. } Not optimized Simulation of thermal effects in Advanced Virgo Test Masses • 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 Optical path length for different CO2 powers Advanced Virgo Meeting - 16.07.08

  9. } Not optimized Simulation of thermal effects in Advanced Virgo Test Masses • 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 Temperature map for 9.7W of CO2 HR face displacement for 9.7W of CO2 Advanced Virgo Meeting - 16.07.08

  10. } Not optimized ROC=1567 m ROC=1556 m ROC=1538 m ROC=1530 m Simulation of thermal effects in Advanced Virgo Test Masses • 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 ROC for different CO2 powers Advanced Virgo Meeting - 16.07.08

  11. ROC=1518 m ROC=1538 m ROC=1530 m Simulation of thermal effects in Advanced Virgo Test Masses 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. 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. Simulation of thermal effects in Advanced Virgo Test Masses From the simulations it follows: • 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. Simulation of thermal effects in Advanced Virgo Test Masses CO2 heating on both faces 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. Effect on the ROC Advanced Virgo Meeting - 16.07.08

  14. Simulation of thermal effects in Advanced Virgo Test Masses CO2 heating on both faces Effect on the OPL Temperature map OPL Advanced Virgo Meeting - 16.07.08

  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 LIGO Laboratory 15

  16. Flexure Noise- A Simple Model CM line heating slat mirror probe beam heating A 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 16

  17. Ad Virgo TCS noise Zemax profile Fit Evaluation of the flexural noise Heating profile from Zemax fitted with: W/m2 w1=0.099 and w2=0.0048 This profile has been fed to a structural simulation in COMSOL to calculate the displacement of the HR face wrt the CM Advanced Virgo Meeting - 16.07.08 17

  18. Ad Virgo TCS noise 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 A cross check between the model with experimental data (Edwige from TCS commissioning) and analytical calculations (S. Ballmer) is in progress In case of heating on both sides of the TM, the noise model must be reviewed to take into account possible cancellation mechanisms. Advanced Virgo Meeting - 16.07.08 18

  19. Simulation of thermal effects in Advanced Virgo Test Masses Heating ring actuation 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. 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. Preliminary Advanced Virgo Meeting - 16.07.08

  20. Simulation of thermal effects in Advanced Virgo Test Masses Heating ring actuation Temperature distribution in the mirror (cold mirror at T= 295 K) Displacement of the HR face Preliminary 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 Preliminary Effect on the ROC 160 W delivered by the Heating ring. Temperature of the HR = 530 K Detailed calculations not yet performed (need to model the LG33 effect). Thermal lensing is probably overcorrected! This is possible only on ETM 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 Advanced Virgo Meeting - 16.07.08

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