20-22 july 2006 maddalena mantovani automatic alignment noise improvement m. mantovani, h....

20-22 July 2006 Maddalena Mantovani

Automatic AlignmentNoise Improvement

M. Mantovani, H. Heitmann, J. Marque, P. Ruggi


Automatic Alignment Status

tx PR BS NI NE WI WE

ty PR BS NI NE WI WE

Present Configuration6 loops under Drift Control (low bandwidth) and 4 under AA (full bandwidth)

DC AA LC (DC signals)

~10h of stable lock


Control noiseThe 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


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;



Optimization criterionOptimized filterComparison filter



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).

100 100


Noise Propagation during C7Estimated centering of 10mm.

The electronic noise dominate the dark fringe

signal up to ~90Hz


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


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.


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

20-22 july 2006 maddalena mantovani automatic alignment noise improvement m. mantovani, h....

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