Sheila, TJ, Camilla
We've had 3 locklosses since 9th Dec from PI24 ringing up (10.4kHz on ETMY): last night 81883, Tuesday AM 81862 and the 9th Dec, plot of all.
We had locklosses like this in September after the vent, Oli has a timeline in 80299. We increased the ETMY RH on September 26th 80320 and didn't have any PI locklosses since.
We normally damp this PI during the start of thermalization and successfully damped this after a 13 hours locked on 10th Dec, plot.
We can see a 25Hz wiggle in DARM just before the lockloss, e.g. 81862. The lockloss tool isn't tagging these as DCPD Saturation so we should implement LLO's PI code: Locklost Issue #198
Plotted is the location of the arm higher order modes around 10kHz. They have moved so that the central frequency is the same as the spikes around 10.4kHz, this excites the PI's more.
- In the first plot we see that since November and the start of December, the center of the lower HOM peak has drifted down in frequency to be underneath the 10.kHz PI modes: compare black (now) to red and brown.
- I tried to check more times to see exactly when this change happened in the 4th attached plot but this is tricky as the location and shape of the HOM depends on how warm the IFO is (i.e. was it DOWN a logn time before locking as in ref 7: Cold IFO). It sees like the change started 6th/7th Dec and was done by 10th Dec.
- In the second plot we see what happened in September when we increased the ETMY Ring Heater (as we repeated today 81891), both HOM peaks moved up in frequency, which is the direction we want.
Maybe an unrelated point is that since the start of October, the circulating arm power has drifted down ~4kW (~1%) from 389 to 285kW when thermalized, plot attached. It's hard to know what's caused this, the IM4 TRANS drifted ~2% but was misaligned so would see alignment shifts 81735, the POP also drifted ~1% before it was recentered 81329. Input power measured by IMC_PWR_IN remained constant.
You cannot just use L1's lockloss code for the tagging universally [should work for the 10kHz PI though].
Because of the way LHO changed their readouts for the OMC, digging into the simulink model will reveal the PI is reading in only the first 32kHz band, for the RMS calculations
You simply have no aliasing down of the full band to utilise it in the way we do; and it will never see 80kHz PI.
Also your scaling is using calibrated DARM units by the look of things; while we use a counts scale; so the numbers in the RMS readouts are different many orders of magnitude.
Very quick shot of the 10.4k homs 2 hours into the first lock with the EY ring heater bumped up to 1.2W from 1.1W. This will need to be checked again later, but it's promising so far.
