A recent suggestion is that we see if the BS coil drivers are a limit to our sensitivity now. The way we'd check is to put the BS back to it's acquisition state, and see if we see noise in DARM. Any excess noise can then be projected down with the ratio of the coil driver filters.
I took an old version of a coil state switching script (from userapps/isc/guardian/bs_m2_switch_fast.py), and added to it turning off the output gain (upon recommendation of LLO who suspects that as contributing to their lockloss). We don't have time to try it out today, but the script (attached here, as well as checked in to userapps) should be ready to try next week. We can consider running it on Tuesday morning just to check that there are no issues with it, but then actually try it Wednesday afternoon.
To turn the BS to it's actuation state, line 12 setting the 'actuatorState' variable should be set to 2, then run the script. Then, to go back to the lownoise setting, change that variable back to 3 and re-run the script.
Note that the BS suspension guardian can take us from the acquisition state to the low noise state gracefully, but it doesn't look like it's got built-in a graceful way to go back to the high noise state.
We were not locked (due to an earthquake) at the beginning of maintenance, so we have not yet tried this with the IFO locked.
However, I ran it a few times during maintenance and it seems to work. I did need to update the script to convince it to work with python3 (the version I started with was quite old). I attach the updated script here, but it's also still in userapps/isc/h1/guardian/bs_m2_switch_fast.py
I see some small motion in the BS optical lever siganls when I do the switching, particularly from the low noise state to the high range state (3->1->2), but I'm still working on convincing ndscope to lookback at data from the last time we went through ISC_LOCK state 552 (lownoise_coil_drivers) to see what scale of oplev motion we normally survive in that state.
I might try running this once or twice as we acquire lock after maintenance today, but otherwise this is probably as ready to go as possible in preparation for trying it during a commissioning time.