Starting right around 21:00 local, the 25.4 hz (well, DTT says something like 25.37) peak showed back up, creating a nasty looking comb in the DARM spectra (first image). Unsure of what else to do, I turned the power down to 16 watts, the peak has now kind of subsided(second image). I'll wait to see if the peak settles down any more, then maybe turn the power back up.
Dan called in and helped me look for a PI with a template he had ready. There were 2 peaks rung up at 15516 and 15540, see attached plot. The main culprit causes the big bump in the RMS, the little peak next to it was also rung up more than Dan's quiet reference. We were trouble shooting when the IFO lost lock. Guardian is bringing everything back up.
Thanks, Jim!
The channel H1:IOP-LSC0_MADC0_TP_CH12 is the 64kHz-sampled IOP input for OMC DCPD A.
Recall that the frequency of this mode matches what Elli measured for our parametric instability.
The other approach would be to change your ring heater power. I guess you in the same situation as us from the fact that the previous step up in ring heater power was effective. So you need to increase your ring heater up from 0.5W per segment, which is what I think it was set to after your first observation of parametric instability. At Livingston if we increase the ring heater too much we then ring up a 15004Hz mode. There is a new wiki here for operators as we had an apparent change in the parametric gain after last vent and we are still in the process of finding a new operating point for the ring heater.
The two acoustic modes appear to ring up with a similar time constant see image, there is also a peak in DARM a bit further down ldvw link any idea if this is related? It's a bit big for an acoustic mode that is not ringing up.
I would guess that these two modes are ETMY and ETMX ringing up with the vertically oriented mode, as that is what we mostly see at Livingston. You could look at the transmission QPD channels for more information if you are interested.
At Livingston these channels are L1:IOP-ISC_EY_MADC1_TP_CH0-7 for X and Y end, pitch and yaw orientations can be derived.
