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Entry  Fri Nov 18 15:45:11 2011, Mirko, Update, IOO, Mode cleaner noise projection WholeMCNoiseProjection.pngWholeMCNoiseProjection.fig
    Reply  Fri Nov 18 19:57:19 2011, Mirko, Update, IOO, Mode cleaner noise projection MC_ELP.pngWithAndWithoutHPs.pdfSeismCoh.pdf
       Reply  Fri Nov 18 23:44:33 2011, rana, Update, IOO, Mode cleaner noise projection 
          Reply  Sat Nov 19 01:26:16 2011, Den, Update, IOO, Mode cleaner noise projection 
          Reply  Sat Nov 19 12:57:55 2011, Mirko, Update, IOO, Mode cleaner noise projection CouplingMClengthsToMCF.pdfNpModeCleaner.pdf
Message ID: 5953     Entry time: Fri Nov 18 23:44:33 2011     In reply to: 5952     Reply to this: 5957   5960
Author: rana 
Type: Update 
Category: IOO 
Subject: Mode cleaner noise projection 

Could use some more detail on how this measurement was done. It looks like you used the SUSPOS signal with the mirror moving, however, this is not what we want. Of course, the SUSPOS with the mirror moving will always show the mirror motion because the OSEMs are motion sensors.

Instead, what we want is to project how the actual OSEM noise in the presence of no signal shows up as MC length. For that we should use the old traces of the OSEM noise with no magnets and then inject that spectrum of noise into the SUSPOS filter bank with all the loops running. We can then use this TF to estimate the projection of OSEM noise into the MC length.

As far as improving the damping filter, the 2.5 LP is not so hot since it doesn't help at low frequencies. Instead, one can compute the optimal filter for the SUSPOS feedback given the correct cost function. To first order this turns out to be the usual velocity damping filter but with a resonant gain at the pendulum resonance. This allows us to maintain the same gain at the pendulum mode but ~3x lower gain at other frequencies.

In the past, we had some issues with this due to finite cross-coupling with the angular loops. It would be interesting to see if we can use the optimal damping feedback now that the SUS DOFs have been diagonalized with the new procedure.

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