Every lockloss after Tuesday maintenance last week has run up the violins.
Even though before this last lockloss the fundamental mode was very low (but harmonics were still elevated) the IFO has relocked with very high violins. Attached is the violins screen and DARM at the LOWNOISE ISC_STATES before we get to NLN.
They look much better now (after few hours of damping) - see screenshot attached (red trace is the current value, blue and green is old data). Not sure what is causing them to ring up after every lockloss. I will keep tracking them, especially after lockloss and new lock acquisition.
I just had a thought, although I'm not sure how much credibility it has. Our higher order violin modes have also been quite high the last week or so. I wonder if we had one as-yet-undetermined something that kicked up all the modes, and then now between locks there's energy transfer from those higher order modes (that we don't damp in lock, so they haven't really been getting smaller) to the fundamental modes. Then each lock we damp the fundamentals (and some of the 1kHz modes), but then the next lockloss puts a little more energy into the modes, and again there's energy transfer between the modes. Would we help this situation if we damped more of the higher order modes? Even if it doesn't directly help, getting those modes damped is probably a good idea (although generally a low priority, since they usually aren't a problem and we have many higher priority items).