I posted the following message in the Detchar-LHO mattermost channel:
Hey detchar! We could use a hand with some analysis on the presence and character of the glitches we have been seeing since our power outage Wednesday. They were first reported here: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=86848 We think these glitches are related to some change in the input mode cleaner since the power outage, and we are doing various tests like changing alignment and power, engaging or disengaging various controls loops, etc. We would like to know if the glitches change from these tests.
We were in observing from roughly GPS time 1441604501 to 1441641835 after the power outage, with these glitches and broadband excess noise from jitter present. The previous observing period from roughly GPS 1441529876 to 1441566016 was before the power outage and these glitches and broadband noise were not present, so it should provide a good reference time if needed.
After the power outage, we turned off the intensity stabilization loop (ISS) to see if that was contributing to the glitches. From 1441642051 to 1441644851, the ISS was ON. Then, from 1441645025 to 1441647602 the ISS was OFF.
Starting from 1441658688, we decided to leave the input mode cleaner (IMC) locked with 2 W input power and no ISS loop engaged. Then, starting at 1441735428, we increased the power to the IMC from 2 W to 60 W, and engaged the ISS. This is where we are sitting now. Since the interferometer is has been unlocked since yesterday, I think the best witness channels out of lock will be the IMC channels themselves, like the IMC wavefront sensors (WFS), which Derek reports are a witness for the glitches in the alog I linked above.
To add to this investigation:
We attenuated the power on IMC refl, as reported in alog 86884. We have not gone back to 60 W since, but it would be interesting to know if a) there was glitches in the IMC channels at 2W before the attenuation, and b) if there were glitches at 2 W after the attenuation. We can also take the input power to 60 W without locking to check if the glitches are still present.