Jordan, Sheila
In the summary pages, we can see that something non stationary appeared in DARM from about 80-250 Hz durring the long lock that spanned Oct 11th to 12th, and has stayed around. Links to the spectra from the 11th and the 12th.
HVETO also came up with a lot of glitches in this frequency span starting on the 12th, (here) which were not around before. These glitches are vetoed by things that seem like they could all be realted to corner statin ground motion: refl, IMC and AS WFS, all kinds of corner station seismic sensors, PEM accelerometers, MC suspensions.
Although this noise seems to have appeared durring a time when the microseism was high for us, I think it is not directly related. (high microseism started approximately on the 9th, 2 days before this noise appeared and things are quieting down now but we still have the non stationary noise sometimes up to 200 Hz.)
The blend switching could also seem like a culprit, but the blends were not switched at the begining of the lock in which this noise appeared, and we have been back on the normal (90mHz blends) today but we still have this noise. We've seen scattering from the OMC with velocities this high before (17264 and 19195).
Nutsinee and Robert have found that some of the glitches we are having today are due to RF45, but this doesn't seem to be the case on the 12th.
Robert, Sheila, Nutsinee
The first plot attached is a timeseries of DARM vs RF45 mod of the 10/11 - 10/12 lock stretch (~25 hours). The second plot is the same channels during the beginning of 10/13 lock stretch (30 minutes). You can see RF45 started to act up on 10/13. I've also attached the BLRMS plot of DARM using the bandpass filter Robert used to find the OMC scattering. The none stationary noise we see is likely caused by two different sources.
RF45 started to glitch Monday afternoon (16:04 PDT, 23:04 UTC). According to TJ's log no one was in the LVEA that day. The glitches stopped around 03:22 UTC (20:22 PDT)
Here is one example of one of these glitches rlated to ground motion in the corner that we had durring high microseim over the weekend (but not the entire time that we had high mircoseism). This is from Oct 12th at 14:26 UTC. Even though these have gone away, we are moitvated to look into them because as Jordan and Gabriele have both confirmed recently, the noise in the unexplained part of the spectrum (50-100 Hz) is non stationary even with the beam diverter closed. If the elevanted ground motion over the weekend madde this visible in DARM up to 250Hz, it is possible that with more normal ground motion this is lurking near our sensitivity from 50-100 Hz.
If you believe these are scattering shelves.
See josh's alogs about similar problems, especially 19195 and recently 22405
One more thing to notice is that at least in this example the upconversion is most visibe when the derivative of DARM (loop corrected) is large. This could just be because that is the time when the derivative of the ground motion is large.
Nairwita, Nutsinee
Nairwita pointed out to me that the non-stationary glitches we're looking at was vetoed nicely by HPI HAM2 L4C on October 12th, so I took a closer look. The first plot attached is an hour trend of DARM and HPI HAM2 L4C. But if I zoom into one of the glitches it seems to me that there's a delay in response between HPI and DARM up to ~10 seconds from just eye-balling it (second plot). I've also attached the spectrogram during that hour from the sumary page.