E. Capote, J. Kissel, S.Dwyer

The ~1 Hz ring-up that had been marginally stable and transient is now fully unstable during the lock acquisition sequence as we recover from maintenance. The suspicion is that the change in ITM M0/R0 satamps might have changed the top mass damping loop OLGTF enough to augment the damped plant that's the plant for the never-really-well-designed L2DAMP that takes the L2 (or PUM) OSEMs and feeds back their sensor signal to the reaction chain top mass OSEMs actuators. But also, we've never measured these loops in any substantial form, so we wanted to just see what they were doing.

Attached are the results. Here're the templates:
    /ligo/svncommon/SusSVN/sus/trunk/QUAD/H1/ITMY/SAGR0/Data/
        2025-07-08_2240UTC_H1SUSITMY_R0_WhiteNoise_0p02to50Hz_L2DAMP_OLGTF_P.xml
        2025-07-08_2240UTC_H1SUSITMY_R0_WhiteNoise_0p02to50Hz_L2DAMP_OLGTF_R.xml

Very little loop gain and only at 3.3 Hz. The loop stability is questionable at that frequency -- for a few averages the suppression (i.e. the gain peaking) looks really sharp around 3.3 Hz. 
T'was really tough to get good coherence; the excitation is pretty well tailored, but it's tough to fight the 1/f^6 suppression of the physical suspension and dirt coupling.
I had to turn OFF the R0 alignment offsets to get this data for pitch. (They were ON for the Roll measurement).

So -- perhaps not the source of the ~1 Hz IFO instability, but boy could this loop use some TLC in order to more effectively achieve its goals...