thomas.shaffer@LIGO.ORG - posted 00:13, Sunday 07 July 2024 - last comment - 09:05, Monday 08 July 2024(78913)
Lock loss 0642
Lock loss 1404369750
Again, not seeing much of anything on any of the plots. Another 4-5 hour lock.
Hey so I had a quick squiz whether your locklosses might be PI related. The regularity of your lock lengths is very suspicious.
You had at least one lockloss from a ~80296 PI on July 5th just after 6am UTC.
Since then you have been passing through it, exciting it, but surviving the PI-Fly-By.
On those plots you will notice broader a feature that moves slowly up in frequency and excites modes as it passes (kinda vertical-diagonalish on those plots) that smells like the interacting optical mode to me.
Last couple of days you have lost lock when that feature reaches ~80306, where there's a couple of modes which grow a little in amplitude as the broad feature approaches.
It is hard for me to say which mechanical mode had the super high gain that would make you lose lock on the scale of seconds [because these modes would move wildly in frequency at LHO as I discuss in the link at the end of this line], but its in that ballpark,and I quote myself: avoid at all costs.
Please investigate if this is PI and whether you need to tweak up your TCS.
EDIT: Longer lock on the 8th makes me think 80kHz PIs are probably fine. Worth double checking carefully in the 20-25 kHz region since your mode spacing looks pretty high. It might be subtle to see in the PI plot on the lock pages since that aliases a lot of noise all over the place.
Thanks for pointing us to these PI locklosses out Vlad, Ryan also caught one of them in 78867, 78874.
The lockloss website for the July 5th 637UTC lockloss 1404196646 tags OMC_DCPD and can see elevated noise on the "PI Monitor" dropdown on the website too, maybe peaks at 15 and 30kHz.
Edit2: There are some elevated peaks at many frequencies before a lockloss I chose to look at, but nothing alarming enough. The largest peak change is something at 3619 Hz, which could be a red herring or aliased from a much higher frequency, but I don't know what that peak is.