naoki.aritomi@LIGO.ORG - posted 20:39, Sunday 14 April 2024 - last comment - 06:32, Tuesday 16 April 2024(77164)
SQZ issue
Vicky, Naoki
In the last lock, the FC IR kept unlocking. We first thought the timer issue similar to 76280 so we removed the timer, but it did not help. We checked the FC IR OLG and it was fine. Then we found that the FC ASC input signal moved a lot. We turned off FC ASC and the stability was improved. We decided to go to observe without FC ASC tonight.
As a separate issue (I think) than FC not locking, the pump ISS control voltage was dropping below 2V and losing lock. I aligned the fiber polarization, but more importantly sent more power from the pump aom to the fiber, aka reduced the rejected power on H1:SQZ-SHG_REJECTED_DC_POWERMON, to keep pump ISS locked. On a Tuesday with extra time, might be worth checking if the pump path alignment (pump aom + fiber) is still good.
Once we got back to NLN, continued to have the issue with SQZ_FC unlocking. Naoki & Vicky continued to work on it.
Currently we have SQUEEZING.
To get to OBSERVING, I had to ACCEPT some Diffs (see attached).
If the SQZ_FC unlocks again, Operators should take steps to put H1 in NLN + NO SQUEEZING (I'm set up to follow the procedure to do this if it happens in the next 45min, otherwise, I sent a text to the OWL shift operator.)
See LHO:77188 - these FC locking issues seem correlated with >30-40 mph winds, likely moving FC2 SUS too much to hold lock. We had seen the FCGS trans beam (on SQZT8 in FCES) moving a lot on the camera, which suggested the FC cavity axis was moving a lot. This is why we disabled FC ASC this night. If that helped, it's b/c FC2 SUS, aka the FC cavity axis, was moving due to winds. We traced this down the following night 77188 when higher winds prevented even FC green VCO locking, and we saw the FCGS control signal was railing and correlated with FC2 SUS motion with no control signal.
Both nights (this and following one) - FC locked overnight once winds calmed down, see screenshot.