During the current lock and after being at NOMINAL LOW NOISE on the order of 45 min, all of a sudden have begun to see a broadband bump on DARM (attached is a screenshot showing instance where the bump is seen on the DARM spectrum & you can also see how often it is occurring on the DARM BLRMS striptool). It is also seen on DMT Omega. The range has only taken a small hit of about 5Mpc (down to 112 Mpc from 117Mpc).
Only difference I accepted for this lock was the enabled filter for ASC PRC1_P FM1 (-20dB).
Will start taking a look at the H1 Summary Pages to see if I can glean anything from them.
Note:
- I increased the Y-axis on DARM BLRMS for the 500-1k & 1k-2k axis from 0.100 to 0.300 so this noisy period could be viewed on the StripTool.
- From 12:37 to now (~8min) it has not been noticeably observed.
The DCPD sum-to-null ratio calculated as a squeezing diagnostic jumps up in these bands at the time of the noise, then goes back down. Attached is a timeseries, with the excess noise period from 12:14 to 12:37. Also a spectrum of DCPD sum and null. This seems like it could be an error in squeezing angle. There was also a half-hour period yesterday at 1:30 UTC where the same kind of noise happened. Jake Slutsky suggests that this could be tested by shuttering the squeezer. If the noise comes back, you could try going out of observing and closing the shutter for a few minutes (if this wouldn't break anything).
Thank you for the quick response, Andy! (I tried looking at the Summary Pages, but many didn't have recent data posted (I did see this noise for IMC Freq Noise...see attachment #1).)
Attachment #2 is a plot showing how this period of noise has stopped *knock on wood*.
What To Do When It Returns
I've actually not had experience with closing a Squeezer shutter (guardian generally handles all things Squeezer for us). But after snooping around, I see that there is a "SQZT6 CLF" Shutter on our Shutter Summary medm window (see attachment#3 for a screenshot showing this shutter). I wonder if this is the shutter one would use to close a Squeezer Shutter when investigating this noise.
After checking many more things, I find that there's a lot of noise in the FSS. Attached is a spectrogram of FSS fast, and spectra of that and the FSS mixer channel. There's a much smaller increase in ISS noise. This seems more likely to be the cause that either the IMC or the squeezer, since it's upstream of both of them. So I would suggest checking the health of the FSS loops (and maybe nearby things like PMC) before trying anything else. That's assuming this noise returns.
Seems like something was going on out of the band in FSS (look at PC MON, yellow) though we cannot say if it was from FSS servo itself or laser.
Noise eater (H1:PSL-MIS_NPRO_RRO_OUTPUT) was within its nominal range of -5852+-50, ISS was OK, these two are exonerated.
Tidal was not railing anywhere.
Next time this happens, please run the dtt template here: /ligo/home/keita.kawabe/Templates/FSS_highfreq.xml
This looks at IOP channels, we can only see things up to ~30kHz so the chances of seeing something is not that high but it's better than nothing.
@DetChar & TJ Massinger -- can you plot the same spectrograms of PSL-FSS_MIXER_OUT_DQ and IMC-F as you did for LHO aLOG 51260? Leading question: are these two aLOGs (51260 and 51053) documenting a similar noise problem?