20-22 July 2006 Maddalena Mantovani Automatic Alignment Noise Improvement M. Mantovani, H. Heitmann, J. Marque, P. Ruggi

20-22 July 2006 Maddalena Mantovani Automatic Alignment Status txPRBSNINEWIWE tyPRBSNINEWIWE Present Configuration 6 loops under Drift Control (low bandwidth) and 4 under AA (full bandwidth) DC AA LC (DC signals) ~10h of stable lock

20-22 July 2006 Maddalena Mantovani Control noise The AA control noise dominates the sensitivity up to ~100 Hz. To reduce the noise: improve the decoupling of the AA control loop (improve the Matrix) improve the electronic noise reduce the re-injection of the control noise by improving the roll-off Automatic Alignment Status C7 During C7 10 loops of AA system (full bandwidth) were engaged

20-22 July 2006 Maddalena Mantovani AA Filter Optimization Developed a Matlab script to optimize the AA control filters the script optimizes the total open loop transfer function of the AA control loop (mechanical filter and control filter) by acting on the AA filter with an N- dimensional scan (on the zero/pole frequencies and on the quality factors) with a scan rate of ~2.3 msec/config. Input: gain margin and maximum overshoot required for the new filter mechanical TF and the AA filter TF to optimize vectors of poles/zeros with Q factors to add optimization criterion % POLES: F = [logspace(log10(6),log10(10),10)]; Q = [logspace(log10(0.5),log10(4),3)] ; pz(line,1:length(F)) = F; line=line+1; pz(line,1:length(Q)) = Q; line=line+1;

20-22 July 2006 Maddalena Mantovani AA Filter Optimization Optimization criterion Optimized filter Comparison filter

20-22 July 2006 Maddalena Mantovani AA Filter Optimization Tx Ty These filters have a better cut-off above the u.g.f. in order to reduce the noise re-injection, moreover there are simpler and lighter with respect to the old ones (due to a series of historical features removed and optimized). 100

20-22 July 2006 Maddalena Mantovani Noise Propagation during C7 Estimated centering of 10mm. The electronic noise dominate the dark fringe signal up to ~90Hz

20-22 July 2006 Maddalena Mantovani Noise Propagation (Opt configuration C7 filters) Estimated centering of 1mm. We have optimized the power impinging on the quadrant diodes in order to be shot-noise limited. The electronic noise dominates the sensitivity up to 30Hz

20-22 July 2006 Maddalena Mantovani Noise Propagation (Opt configuration Opt filters) Estimated centering of 1mm. We have optimized the power impinging on the quadrant diodes in order to be shot- noise limited. The electronic noise does not dominate the dark fringe.

20-22 July 2006 Maddalena Mantovani Conclusions The sensitivity at low frequencies is completely dominated by the alignment control noise. It has to be reduce by: improving the signal decoupling improving the control filters improving the electronic noise Developed a matlab script to optimize the control filters The alignment electronic noise can be reduced below the Virgo design sensitivity