J. Kissel, P. Covas

Part of the focus of Pep's current LSC fellowship was to continue work mitigating sharp features in DARM to help out the CW group's search sensitivity. Recently, he's suspected that features in the ~15-50 Hz region of DARM (and confirmed in PRCL and SRCL as well -- see LHO aLOG 48947) are corner station triple suspensions, predicted to have their highest frequency vertical (a.k.a "bounce") and roll modes (V3 and R3) in this region. As such, we've remeasured all of these suspensions' V3 and R3 mode frequencies, using this morning's maintenance period to complete the inventory -- see LHO aLOG 49643.

Armed with this inventory, we then perused all triple suspension notches for these mode frequencies. Below are the list of changes we've made based on our findings, and the expected features that the changes are expected to improve -- ranked by the hopeful amount of improvement.

SR3
    - [Attachment 1]Changed/fixed the frequencies of FM9 "SB27.7" and FM10 "SB45.3" elliptic bandstop filters in the M1 DAMP banks for every top mass DOF (L, T, V, R, P, Y).
     >> We expect this will reduce the 27.71 Hz feature in DARM.

PRM
    - Turned ON FM8 "SB27.5" and FM9 "SB40.9" elliptic band stop filters that were already there in the M1 DAMP banks for every top mass DOF (L, T, V, R, P, Y).
     >> We expect this will reduce 27.59 Hz and 40.87 Hz features in DARM.

BS
    - [Attachment 3] Added previously non-existent FM8 "SB17.79" and FM9 "SB26.06" elliptic band-stop filters in the M1 DAMP banks for every top mass DOF (L, T, V, R, P, Y).
    - [Attachment 2] Updated the frequencies of the FM5 "NotBR_BS" elliptic band-stop filter collection in the optical lever OLDAMP banks for P and Y.
     >> We expect these actions will help reduce the 17.79 and 26.06 Hz features in DARM.
    - [Attachment 4] Turned OFF FM2 "not19.1" and FM3 "not23.1" elliptic bandstop filters in the M3 ISCINF P and Y banks. These, we believe, are unneccessary -- intended to be temporary -- notch filters single-line oscillator excitations for exploratory ASC loop tuning. These were accpeted inthe SDF by Jeff Kissel back in Oct 2018 (see LHO aLOG 44277) during the height of commissioning, and were likely just accidentally left ON after a night of loop tuning.
    >> We expect this will claw back a bit of phase for the MICH ASC loops, but otherwise have little to no effect (other than cleaning up an unneeded mess.)
    - Changed the names of FM5 "NotBR_BS" and FM7 "NotBR_Quad" from their original ambiguous names "BounceRoll" and "EvanBR"
    >> We expect no change  in DARM from this change, just cleaning up the filter banks.

PR3
    - Moved FM2 "SB46.09" elliptic band stop filter in to FM10 (overwriting the unused, incorrect frequency filter that was there before) in M1 DAMP bank, in order to 
     >> We expect no change in DARM from this change, just making PR3's filter location consistent with every other SUS.

For all of the above changes, the new settings have been saved into both the safe.snap and OBSERVE.snap such that they stick.

MC2
    - [Attachment 5] We *looked* at the various implementations of notch filters for the highest bounce and roll modes (V3 and R3) for MC2 (and comparing against MC1 and MC3), but decided that the notches were well centered enough, and because we don't see any of MC2's resonances in DARM, we elected not to make any changes.

All other corner station suspensions have been confirmed to have correct notches for their newly re-measured highest bounce and roll (V3 and R3) modes.