Craig, Georgia, Jeff B, Patrick

Lock reacquisition

We accidentally lost the 24 hour lock during an excitation (1237609866). Patrick did an initial alignment, and we reacquired lock with the ring heater settings as Jenne had left them (0.1 W on ITMX and 1 W on ITMY). I thought that the AS_AIR camera looked a bit funky, but maybe it's always like that? See first attachment for a screenshot taken at the LOWNOISE_COIL_DRIVERS state. We made it to NLN and hung out for 3 mins before losing lock to a fast-ring-up 0.48Hz oscillation in ASC pitch loops (1237616294) see second attachment for ASC control signals. Based on the oplevs it seems that CSOFT was the issue.

Given the link between ASC and TCS, Craig lowered the ring heaters back to their nominal values (0.4 W on ITMX and 1.3 W on ITMY). Note that there seems to be a 0.1 W offset between the inverse_filter_in and the final power the ring heater actually gets set to, (edit: there's nothing wrong with the filter, I was just too impatient with the ring heaters) so we've requested powers 0.1 W above what is written above. We reached NLN again and lost lock after 5 mins again due to the ASC pitch ring up (1237618224), possibly because the thermal state of the IFO was still settling.

In the next lock we chilled out at POWER_30W, and found the 0.48 Hz oscillation ringing threateningly. I increased the CSOFT_P gain and this seemed to help. It turned out this gain was going to be turned up in LOWNOISE_ASC anyway. We went to NLN and have been locked fine, and observing, since then.

Noise budget

I re-ran the noise budget injections for CHARD_P, CHARD_Y, and added templates for DC2_P DC2_Y, after Jenne noted excess coherence between DC2_Y and DARM last week. The third attachment is the ASC noise budget as of today. The DC2 centering loop did not show elevated coherence with darm even with an excitation a couple of orders of magnitude above ambient, but there is still ~0.2 coherence around 23 Hz without an excitaiton, I'm not sure what is going on there. Meanwhile, CHARD_P is limiting us between 10 and 20 Hz, not too surprising as its cutoff was relaxed last week. Final attachment is the full noise budget.