I performed the lockloss investigation for the recent lockloss from the OBSERVATION state of the LSC_LOCK guardian, between 2025/03/18 04:43:0 UTC and 3/19 15:40:20 UTC. The previous lockloss investigation was posted in klog33036.
During this period, there were 47 lockloss. The plots are summarized in wiki.
1Hz seismic motion made the IMC lockloss
For 8 lockloss, we saw the excess of the seismic motion with 1~10 Hz, which made the oscillation of the IMC length control and made the IMC lockloss.
Oscillation of MICH and PRCL with 1.65 Hz
For 1 lockloss (2025-03-20 01:27:34.437500 UTC), there was an oscillation in the MICH and PRCL error signals with 1.65 Hz (Fig). I didn't find the coincident oscillation in the oplev signals.
Oscillation of ITMY and ETMY with 0.9 Hz (or 0.88Hz?)
For 3 lockloss, there was an oscillation in the ASC signal (especially CSOFT) with 0.9 Hz (Fig). For one lockloss, there are coincident oscillations in the PRM pitch, PR2 pitch, and ITMX pitch with 0.88 Hz (Fig).
- 2025-03-20 05:56:20.812500 UTC
- 2025-03-20 06:14:23.062500 UTC
- 2025-03-20 09:07:25.562500 UTC
Oscillation of OMC PD over minutes
The amplitie of OMC PD looks growing over several minutes (Fig).
Others
Sometimes, we saw the saturation of OMC DCPD signals just before the lockloss. Sometimes, there was no saturation. In addition, the time it takes to saturate depends on the case. The cause of the OMC saturation is still unclear.
Based on Ushiba-san's suggestion, I will try to characterize whether the OMC alignment is good or bad before the lock loss by using the other PD channel at OMMT.
Memo
Even though the lockloss occurred in the end, there was a recovery from the OMC oscillation twice.
