Oli, Elenna

This is incredibly baffling, but we are still seeing locklosses from lownoise ASC due to a 1 Hz ring up. We have stepped through this state multiple times by hand, and we seem to survive when we do the steps very slowly, with 2-5 minute breaks between each step.

The culprit at times has appeared to be either CHARD P or DHARD P (and maybe also the soft loops?). I have looked at the loop design and measurements of both DHARD P and CHARD P but they show stable loop designs with no gain peaking at 1 Hz. DHARD P has a very large 1 Hz peak in it's error signal spectrum, but I don't know where it comes from.

Tonight, I rewrote the lownoise ASC state to step very slowly through each change and wait 60 seconds after each change, but that did not help. After we left the state and moved into the next, the ring up occurred again and Oli and I tried to save the lock by reverting changes. We're not sure if it was the ring up or our change reversion that broke the lock.

I think this may be an ongoing problem that we didn't realize was a "problem" because the ring up likely occurs during the transition from ETMX state, so we might have classified those locklosses as a problem with the transition, and not a problem with an ASC instability.