Vicky and I have been looking into how the 80 kHz PI29 dampens or leads to a locklosses recently (alog 70161) .
I looked between 05/24/23 to 06/06/23 and recorded the few dates that this channel witnessed instability and either dampened or did not dampen the issue.
DAMPENED, 600 NLN, May 27 2023 02:41:18, PI managed to keep the detector from losing lock, this lasted about 6 minutes 19s
DAMPENED, 600 NLN, May 28 2023 04:02:31, PI managed to keep the detector from losing lock, this lasted about 5 min 45s
LOCKLOSS, 600 NLN, May 29 2023 07:42:54, PI did not manage to dampen the mode and the IFO lost lock, this lasted about 2 min 30s (power was changed from 76 W to 75 W after this date)
LOCKLOSS, 600 NLN, June 02 2023 20:13:27, PI did not manage to dampen the mode and the IFO lost lock, this lasted about 3 min 48s
DAMPENED, 600 NLN, June 02 2023 23:55:58, PI managed to keep the detector from losing lock, this lasted about 6 min 8s
Images for reference.
edit:
comparing the two cases that were near eachother on 06/02/23, it seems the first one at 20:13:27 which lost lock the IFO was at NLN and observing for about 2 hours and the second case at 06/02/23 23:55:58 which kept lock the IFO was at NLN and observing for just a bit over an hour only, both had similar power ranges. (image 3).
Great analysis -- is it possible that these PI's are different modes, either different ETMX modes outside of our signal bandpass of PI29, or else modes on different test masses (maybe ITMX) ? Maybe PI 29 DAMPING works for the higher frequency peak (>14760) that is in-band of our PI damping on ETMX, but the lower frequency peak (<14,760) is out of our PLL signal band pass or a different mass, so we don't effectively damp it?
But the 6/2 pink lockloss vs. blue damped peaks are interesting; the time traces suggest we lost lock from it the first time, then damped it the second time. I wonder if it depends on the time in lock, or the arm power at which it shows up? This would also suggest the lower PI is still on ETMX? I think these cases are interesting to look at and undersatnd.
If we continue to have issues, I think it might be interesting to install new PI damping channels/modes for this lower frequency peak (new ones, so we don't lose the maybe-working PI29 channel).