Gabriele ran a recent bruco in CHARD Y, and noticed there was large coherence between CHARD Y and the IM damping loops between 4-10 Hz. The IM damping loops have been updated before to improve noise reinjection into CHARD and therefore DARM. Take a look at alogs 64007 and 64017 for more information. Over the summer, I updated the damping loop cutoff to a high Q elliptical low pass at 7 Hz. There is room for improvement, by reducing the Q of the elliptical filter and moving the cutoff to 5 Hz. There is quite a lot of phase margin in the loops to do this. The new cutoff loses about 11 degrees of phase, but all three damping dofs have 70 or more degrees of phase margin. This new cutoff allows 23 dB less gain at 8 Hz and no change in the Q. Comparison of the damping design is here.

I placed the new cutoff in all IMs and all dofs. I made measurements of IM1 in L, P and Y. The new measurements are saved in "/ligo/svncommon/SusSVN/sus/trunk/HAUX/H1/IM1/SAGM1/Data" as "2023-04-24_2206_H1SUSIM1_M1_WhiteNoise_{dof}_0p05to100Hz.xml".

The new cutoff filters are SDFed.