As mentioned earlier in my shift transition alog, noticed increased noise on H1 through various computers on the wall in the Control Room. For the most part I do not recall any odd activity for the DARM bands in question (10-20 & 20-34Hz), so when they are noisy, it's pretty obvious & so then an investigation begins.
Overall there was a noticeably noisy period, then it died down (but lingered), and then went quiet...but still getting glitches. Unfortunately I only snapped screenshots of the BLRMS striptool. (I was too slow to grab screenshots of the DARM spectra as well as the MICH/PRCL/SRCL spectra.
Since this is a much different feature from the high-freq noise I observed last night, I did not run Keita's measurement.
Here is an updated summary:
- 7:06utc: Noisiness starting on H1
- DARM spectra above reference mainly below ~13Hz
- DARM blrms' 10-20 band is noticeably noisy (as well as 20-34Hz to a lesser extent).
- Attachement 1: How DARM blrms looked with vertical axis not touched.
- Attachement 2: Here vertical axis zoomed out to see how big the noise was! (i.e. for 10-20Hz band (light blue) axis increased from 2500 up to 200,000 counts! And for 20-34Hz band (yellow) axis increased from 20 up to 200counts.)
- I have restored this striptool to its original state.
- LSC strip tools show a noisier than normal PR_GAIN
- MICH, PRCL, & SRCL spectra on nuc4 show a broadband bump from about 8-30Hz
- Surprisingly, BNS range is not too low (it's hovering around 115Mpc)
- 7:23utc: Noise sort of subsiding (but it's smaller glitches have still popped up until 7:48utc!)
- After 7:48 there is a glitch and now the bands in question look much quieter. *knock on wood*
Just to give an update, we have not had the really noisy stretch like we did at the beginning of this current lock, BUT this 8-30Hz noise has not gone away either. Attached is a look at the last 7+hrs & you can see the noise has been fairly regular for the entire lock.
Scanning through Summary Pages tonight's lock as seen with DMT OMEGA looks somewhat similar over the last few days (i.e. since 8/2), and 2nd attachment is looking at 8/5 where we have a long lock which also has this low-freq noise.
Corey -- There's a brief comment in LHO aLOG 51034, and it's come up verbally in commissioning meetings, but not clearly stated in any aLOGs -- sorry for not catching you up! #OwlsAreTough Here's the story: This excess glitchiness below ~15 Hz is a result of the new alignment position of the beam going in to the OMC. We think this alignment position is making the OMC (and thus DC readout, DARM, and DETLAL EXTERNAL) more sensitive to scattered light in and around the OMC. We made this alignment change at the tail end of Aug 1 2019, as a result of the new global alignment position after losing our reference on July 30 -- which is why it's been seen since Aug 2. We're not super happy with it, but it did recover some optical gain that we lost else where. The tentative plan is to reduce the gain of the OMC ASC loops to see if this glitchiness goes away, if that doesn't work, we may consider a new alignment in to the OMC. We'll try to find a way to keep owl shifters better posted!
No worries! I figured this was proably related to recent alignment work (due to the camera bump). I didn't know a whole lot about this recovery because of being away on vacation and then did not have time to catch up on alogs last night due rough 1st half of the graveyard trying to relock H1. THANKS for explaning this though! (OK, time to sleep for tonight's shift.)