[Oli, Elenna]

Oli has taken some lovely BBSS OLG tfs of the damping loops, which show significant gain peaking for the LPY dofs. Oli and I took time to determine how much we should reduce the gain for each of these dofs to get enough phase back to reduce the gain peaking. For each dof we were able to reduce the gain peaking from roughly 15 dB to 6 dB.

For length and yaw, this is a reduction of gain of a factor of 2, for pitch we needed a factor of 2.5

Based on the loop suppression, each dof still shows 20 dB suppression around the modes, so I think should be good for locking.

I put the new gains into FM4, and SDFed this filter to be on. This ensures that the BBSS epics gain should still be -1 for all dofs.

The only tricky dof was yaw, since there is a sharp feature close to 2.5 Hz. However, the resulting OLGTF looks fine.

The attached plots show reference traces from Oli's measurements, and live traces showing the new damping with the reduced gains. Final image is SDF screenshot.