[Sheila, Camilla, Jenne]
We've got a PI ringing up at 10.4276 kHz. Sheila reduced the DARM offset to help keep us from saturating the DCPDs, but we can't go much lower, so this lock might be doomed. I've increased the ETMY ring heater to 1.2 W per segment, since increasing it a bit seemed to help last April (alogs 62636 and 62650). But, the ring heaters are of course slow, so we may not survive this lock, but at least the ring heater will have started heating things up.
We've got a long list of things we wanted to during our next acquisition, so we can work on those while the ring heater thermalizes.
In the attached figure, blue is 24 hours ago (so, about 15 hours into our lock), and green is now, 40.5 hours into our lock.
As a result of this, it seems that our calibration has gone bonkers, so the spectrum and range look much better than the truth. One can check this (roughly) by noting that our live DARM trace at the Pcal lines is much lower than the Pcal lines themselves, so our current "CAL-DELTAL_EXTERNAL" channel is not at all well calibrated right now.
[Louis, Jenne]
I should have thought of this sooner, but Louis and I were on our way out to use the OMC DCPD temporary dongle to measure the DCPDs in analog, to see if this 10.4kHz mode is actually something that is aliased down from some other frequency. However, the IFO lost lock while we were on the way.
We've looked at the DCPD 64kHz channel for a few times over the long lock, and we start to really be able to see the mode in the spectrum at about 13:00 UTC today, which is about 36 hours after we reached NomLowNoise (and about 4.5 hours before we lost lock). So, next time we have a nice long lock, we should consider going to the floor to measure the DCPDs. Since we're interested in this, I've asked Louis and Jeff to leave the temporary dongle in place - we can remove it next week some time.