Figure 1 shows that yesterday the two jitter peaks in DARM were successfully damped and the peak amplitude reduced by a factor of 3 or more.

Recently I had identified the mounts that were responsible for the jitter peaks in DARM that remained after the reduction in table motion from the water cooling system (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=44460), suggesting a broad-band tuned mass damping system. Rick S. pointed out some leftover dampers that had been made for the PMC, based on OMC bench damping investigations (https://dcc.ligo.org/LIGO-T1600494). I recycled some of these parts and mounted them on the U200-A mounts that were creating peaks in DARM.

Figure 2 shows the system, the damper is bolted to the hole on the side of the U200-A that is used for mounting in the other orientation. The manufacturers hole is counterbored so the bolt head does not extend beyond the mount. The extra weight did not deflect the bottom periscope mirror enough to prevent OMC locking.

It took only a couple of minutes to install each, so I think this might be a useful system for all critical mounts in the future. We might make a smaller version for U100-As.

Cheryl also replaced one of the optics because she thought it might be damaged.

Robert, Cheryl