J. Kissel, H. Yu

Having seen a good amount of success with the recently installed H1 SUS ETMY ISI ST2 L to M0 P feed forward filtering (see LHO aLOG 42875), I was curious if we would gain any benefit from installing a similar L to Y feed-forward path, since only L2P paths were installed (LHO aLOG 42851). 

    As such, I've measured the ISI ST2 Longitudinal motion (as measured by the calibrated, projected GS13s) to Test Mass (L3) Yaw motion (as measured by the calibrated optical lever), both with and without a drive of ISI ST2 in the Y direction (not Yaw, Y, as in X, Y ,Z, or aligned with the Y arm).

    The message: if the ISI ST2 L to L3 Pitch coupling (improved by the ISI ST2 to Mo P feed-forward) is good enough, the as-is L3 Yaw is comparable to it. So -- we don't need to implement a feed-forward path.

The first attachment (2141) shows the comparison between (driven) ST2 Long to L3 Pit with the feed-forward ON vs. OFF against the ST2 Long to L3 Yaw, shoing the the improved L to P transfer function is comparable to the existing L to Y coupling. As a side benefit to this confirmation, we also confirm that the ISI ST2 to M0 P feed forward is stable over the ~1 day time scale, with similar improvements in the driven transfer function as was seen yesterday.

The second attachment (2205) shows the comparison between the quiescent ST2 Long to L3 Yaw against driven ST2 Long to L3 Yaw. This shows there's little coherence in the quiescent state.

The driven template can be found here:
    /ligo/svncommon/SusSVN/sus/trunk/QUAD/H1/ETMY/Common/Data/
        2018-07-13_2141_H1SUSETMY_M0_ISIFF_FilterDesign_ISIST2L_2_L3PY.xml