sheila.dwyer@LIGO.ORG - posted 11:24, Monday 23 May 2022 - last comment - 10:27, Tuesday 31 May 2022(63274)
low noise locking today
Sheila, Elenna, Jenne, Georgia, Craig, Dhruva, Jeff K
- When I got here the violins were nice and low after the work that Jenne and Rahul did last night and early this morning.
- I asked Austin and Tony to request nominal low noise, we lost lock after about 2 minutes from a 4.45Hz oscillation, DARM looks like the most likely candidate, but the osciallation also shows up in DHARD, MICH ASC, SOFT, and SRC2 ASC loops. Nothing shows up in the optical levers. The ringing in DARM seemed to start in the guardian state LOWNOISE_LENGTH_CONTROL
- Switched OMC whitening chassis over to A side since the violins are nice and low. Attached screenshot shows OMC anti whitening filters now.
- I wondered if the ResG (DAMR1 FM3) filter which costs us 20 degrees of phase at 4.45Hz and is engaged in LOWNOISE_LENGTH control could be causing our 4.45 Hz instability, so we stopped at LOWNOISE_ESD_ETMX (before this filter is engaged) to try to make a DARM measurement. Before we could get a measurement we lost lock due to the 4.45Hz instability. This is probably some problem with the swtich over to the LOWNOISE ESD.
- Tried to transition to EY UIM + PUM +IX ESD manually doing the guardian steps, lost lock.
- The next lock we found that we were stable transitioning to ETMY UIM +PUM ITMX ESD, and we measured DARM OLG and PUM crossover. We transitioned half way back to ETMX, and checked that the DARM OLG looked the same at 200 Hz. We tried to transition all the way to ETMX and lost lock again.
- This all seems very similar to problems descirbed in 47982, Elenna and I looked through filters and saw that the PUM L2P decoupling filters for ETMY and ETMX are very different, I will add a comparison screenshot tomorow. ETMX L2P decoupling is routed through P2L, ETMY is not.
- We set the guardian flag back to use our O2 DARM actuator, ETMX ESD and ETMY PUM and UIM, this was stable and allowed us to complete all our usual guardian steps. We didn't investigate if we can use ETMY ESD.
- Gerardo opened the gate valve and we had 15 minutes of quiet time locked on POP AIR from 21:43 UTC to 22 UTC, and locked on in vacuum from 23:50 to 00:05 UTC.
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Tagging CAL for the OMC DPCDs whitening switch from temporarily modified OMC B path back to the well-characterized OMC A path. Change was in place by 2022-05-23 16:10 UTC (09:10 PDT) I've just now accepted the change into the SDF system in prep for maintenance -- see attached screenshot.
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Here is the comparison of the ETMY and ETMY PUM L2P decouplign filters that was promised above.
Images attached to this comment
For the record, the L2P decoupling (and L2Y) was off at ETMY during this time. I missed this when I first looked at it because the filters were on and had gain, but the matrix which sends the output either right to P or to the P input of drivealign had both elements 0, so the signal wasn't going anywhere.