Last night we had some alignment issues after a lock loss (alog72854) and Jenne noticed that our jitter noise is higher (alog72853). Comparing two DARM spectra from the summary pages in the first attachment from two days ago to now, the ~120Hz noise is worse, though our higher freqency noise seems better now.
In terms of alignment, Ryan C's Misaligned GUI shows ITMY P being further off compared to near the end of the Sept 11 lock before maintenance, but I'm not seeing that in top mass OSEM values as seen in the 3rd attachment. Interestingly, L1 P seems to be slightly shifted from the reference time, but this isn't seen in M0 or the oplevs.
This GUI also points to SR2 being slightly off in P and Y, which it does seem to be compared to the reference time, but overall doesn't seem that far off from where it normally moves (6th attachment). PRM is another contender with larger alignment moves, but nothing out of the normal between locks (7th attachment).
The ETMs see similar movement as well (ETMX ETMY). Perhaps obvious, the most movement we see is during our move spots [508] and max power [520] states.
FC2 has been moving much more in the last 5 days. Not sure if this is a symtom or a cause, but perhaps this might point to some of our SQZ issues. FC1 shows a similar story, though doens't seem to be as drastic.
All of this to say that I don't notice any major alignment differences, aside from FCs, from before maintenance to now, but there are a few interesting bits to spend some more time looking at.
Since we're into commissioning for the afternoon, I've retrained the Jitter cleaning (and left the laser noise cleaning with the same training it's had for a few weeks), and it seems to very effectively remove this new larger version of the jitter peak. (Blue in the attachment is unlceaned, red is the cleaned data).
From TJ's plots, it looks like the FC1/2 alignments were drifting, but not necessarily that they are more noisy. Some record of recent FC/SQZ alignment and adjustments, in descending order of most to least suspicious:
- After earthquakes on Friday 9/8 (~5 days ago), FC alignment needed manual alignment in pitch to recover 72771; FC2 slider diffs showed up as SDF diffs that were accepted. If this alignment brought the system to a clippy-position, I could imagine issues from scattered light to sub-optimal FC control introducing issues. We are likely within a factor of 10 for sqz/fc backscatter, but this was never tested down to frequencies below 100 Hz, and likely worth doing a backscatter test again in this realistic low-freq regime. Could be worth it to keep investigating this backscatter issue, from tests later in the day 72870 it looks closer than I thought orginally.
- At some point in the last 2-3 weeks, fiber polarizations were aligned but I am not sure if they were optimized for the fiber delivering FC control signals;
this is worth checking.checked this (72870), and it is probably not an issue. - On 8/30, FC related alignments were tested 72579, on the same day that Rahul/Fil/Dave had earlier fixed the bad ADC to resolve the FC1 T3 osem issue 72740.
- ~8/30 we had also adjusted alignments for homodyne, but this *should* all be set back. I haven't seen clear evidence of oustanding issues after homodyne alignments.
- On 9/6, Naoki re-measured the SQZ ASC sensing matrix (ie, ZM5-6) 72725, and we basically set it back to the previous thermalized values we had been using ; b/c this is downstream of FC, I wouldn't think this affects FC at all.
Re: long night of SQZ issues -- I still have no clear idea of what happened then, there is not a consistent nor clear story of the many glitches in the trends looking back. But, there are visible glitches corresponding to the spontaneous unlocks that night as up-stream as SHG (which is 1-2 layers upstream of FC), even the squeezer was DOWN and FC was unlocked and doing nothing. So, I believe the problem was very likely upstream of FC. That's to say, while FC issues might've resulted from the more low-level issues, or resulted from the same root cause as those glitches, I don't think FC itself was causing the glitches that kept the squeezer down that night.