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Influence of compensation plates on LSC and ASC

Influence of compensation plates on LSC and ASC. M. Mantovani and G. Vajente AdVirgo (bi)-weekly meeting October 16 th 2008. Summary. Simulation of effects on longitudinal control system Simulation of effects on angular control system. Length Sensing and Control. LSC: simulation.

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Influence of compensation plates on LSC and ASC

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  1. Influence of compensation plates on LSC and ASC M. Mantovani and G. Vajente AdVirgo (bi)-weekly meetingOctober 16th 2008

  2. Summary • Simulation of effects on longitudinal control system • Simulation of effects on angular control system

  3. Length Sensing and Control

  4. LSC: simulation • Simulation of CP displacement noise coupling to longitudinal error signals and gravitational channel • A mirror with 100ppm reflection added behind IMY, inside PRC • No wedge on CP • Full 125 W input power • Transfer function from CP motion to all longitudinal signal simulated with Optickle

  5. LSC: results • Coupling to ASY_DC and longitudinal error signals Negligible coupling to auxiliary d.o.f.s

  6. LSC: estimate noise projection • Coupling to h computed from simulation • Motion of CP reconstructed in a very conservative way: • Assume in AdVirgo we actuate on input RM • Assume the AdVirgo longitudinal correction is the same as in Virgo • Assume RM and Mirror to have the same mass • Therefore CP motion is assumed to be the same we would have in Virgo

  7. LSC: noise projection • CP motion estimate projected linearly to h AdVirgo correction should be much lower Inserting wedges will largely reduce this coupling

  8. Angular Sensing and Control

  9. AA simulation configuration • Simulation done with Finesse • A mirror with 100ppm reflection added behind IMX • 1 deg wedge on CP • Longitudinal and Angular Lock active Simulations: • CP etalon effect on the Alignment optical gains • Effects of the CP misalignment with respect the IMX mirror • Introduction of thermal effects

  10. Etalon effects on the Alignment optical gains The CP etalon tuning produces an optical gain variation of the order of 1‰ on the AA error signals

  11. CP misalignment effects on the AA control loop The misalignment of the CP front face produces a big effect on the alignment error signals (1.5 nrad of correspective EMX misalignment for a CP misalignment of 10 urad) Angular and longitudinal locks active

  12. Thermal effects • No relevant changes from the CP plane configuration

  13. Conclusions • Longitudinal system • Noise introduced in h by CP should be negligible, even without any wedge • No significant effect on longitudinal control system • Angular system • The CP etalon effect results to be negligible • The CP front face misalignment produces strong effects on the AA error signals up to 0.1 mrad The CP have to be misaligned more than 0.1 mrad with respect to the IMX front face

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