[Alvin, Yuzurihara]
We performed the lockloss investigation for the recent lockloss from the OBSERVATION state of the LSC_LOCK guardian, between 2025-05-23 06:53:34.812500 UTC and 2025-05-25 10:13:01.312500 UTC. The previous lockloss investigation was posted in klog33585. During this period, there were 26 lockloss.
1~10Hz seismic motion made the IMC lockloss
For 3 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.
The time and date are summarized below:
These excess of the seismic motion might be related to the blasting. I don't have the time information of the blasting. So, I'm not sure the relationship.
Oscillation of ASC
For 1 lockloss (2025-05-25 10:13:01.312500 UTC), we observed the oscillation of ASC, especially DHARD_P, DSOFT_P and CHARD_P, as shown in Figure 1 and 2.
The oscillation frequency was 0.077 Hz. As a result, the alignment to the OMC changed and the OMMT2 TRANS increased.
Oscillation and saturation of OMC DCPD
For the rest lockloss, the scillation of the OMC DCPD happened and saturated.
For some of them, we observed the increase of the arraival laser power on OMC DCPD, just before the lockloss.
For 2 lockloss, we can see the oscillation of the OMC DC PD signal with 44 Hz and 40 Hz, respectively.
Caution
Even though the LSC_LOCK guardian was in the OBSERVATION_WITHOUT_LINES state, the excitation was done in the early morining of May 25 (see Figure 3).
It's a good manner to perform the injection after switching the WORKING_WITH_OBSERVATION_WITHOUT_LINES.
