Figure 1 shows coherence between the IMC DC WFS and DARM, with photos of the optic mounts that are producing the jitter peaks, based on this log: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=42551 . The Qs are fairly high so damping should help. One tool that would be useful, is a small tuned mass damper, variable across the 200-800 Hz band, that can easily attach to a U200-A mount with a little clamp or epoxy. A possible clamping scheme is visible in the picture on the bottom left of Figure 1: I have used two commercial spring clamps near the adjustment screws to broad-band damp (via the mass and the red rubber grips) the U200-A mount. The spectrum shows that this and other damping has reduced the Q relative to the other two mounts, but a tuned mass damper on a clamp like this might be useful on the other mounts and possibly on this one. The jitter spectrum also has some fairly high-Q U100-A mounts (see above log entry).

Figure-2 compares DARM, IMC DC WFSs, coherence and table motion for Monday night and for O2. This is a bit premature since DARM and the WFSs are not yet well calibrated, and so I can’t make a definitive comparison of jitter coupling. But in this preliminary look, the change seems consistent with the table motion reduction being the biggest factor. The ~344 Hz peak seems to be a lot lower, and the table motion has decreased by 5 or more in that band. But the 483 Hz peak is in a band where the table motion has not really decreased (it was already low in O2 in this band, compared to nearby bands) and the 483 Hz peak does not seem to have improved by much in DARM. But, again, this is a first look; calibrations to come.

The second page of Figure 2 includes accelerometer signals when the water was off, showing that we could still improve by a factor of a few in the band around 500 Hz. We are planning to improve some water circuits during the vent. It might also be possible to reduce some flow rates.