1. M. Mantovani ILIAS Cascina March 2008 Automatic Alignment system Improvements after the VSR1 M. Mantovani for the Alignment team

2. M. Mantovani ILIAS Cascina March 2008 2 Summary  Installation of the galvo system for the terminal bench quadrant diodes (actually we are using only for one WE bench quadrant)  Angular control system noise performances Optimization of the control filters Improving the sensor electronic noise  Input mirrors angular control Rearranged the end benches optical components and retuned the Gouy phase for the end bench quadrant diodes

3. M. Mantovani ILIAS Cascina March 2008 Why are the galvo useful? The miscentering of the beam on the diode spoils the error signal Translation stages: too noisy (centering rate ~4sec) ‏ Galvo: bandwidth of tens of Hz

4. M. Mantovani ILIAS Cascina March 2008 Q81 galvo installation

5. M. Mantovani ILIAS Cascina March 2008 Asymmetry fluctuations at step 12 Q81 Beam fluctuations on WE bench Q81 Galvo off Galvo on Loop unity gain frequency ~ 20Hz

6. M. Mantovani ILIAS Cascina March 2008 Control Filters optimization Sensitivity improvement improving the high frequency cut off

7. M. Mantovani ILIAS Cascina March 2008 Control Filters optimization improving the low frequency stability improving the low frequency gain of the differential mode improves the accuracy of the alignment, visible also on the dark fringe

8. M. Mantovani ILIAS Cascina March 2008 Sensor electronic noise reductionQ1pAC to control the differential end mode Q21DC to control the common end mode Q81AC to control the BS

9. M. Mantovani ILIAS Cascina March 2008 Sensor electronic noise reduction Starting fro 10 Hz most of the sensors are limited by electronic noise thanks to the new electronics the electronic noise can be reduced

10. M. Mantovani ILIAS Cascina March 2008 End bench optics rearrangement the quadrant diodes have been placed in the optimum Gouy phase to detect the input mirrors

11. M. Mantovani ILIAS Cascina March 2008 Input mirrors control The error signals are able to detect the input mirror angular displacement, but these are strongly affected by the air currents inside the acoustic enclosure. Thus:  the air currents have to be reduced by improving the insulation of the optical bench (not trivial)  the error signals have to be made insensible to the air flow and to the bench motions by retuning slightly the Gouy phases (not clear if it is feasible) Air flow Bench movements

12. M. Mantovani ILIAS Cascina March 2008 Conclusions and next steps The galvos have been installed on the terminal benches, for the moment we are actually using only one of them The angular control system noise can be reduced below the design sensitivity by acting on the control filter performances, on the electronics and on the mirror/beam centring. The input mirrors can be controlled by using the terminal quadrants if the low frequency noise on the sensors can be reduced Improve the beam/mirror centering by using a permanent frequency line excitation on the terminal mirrors