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MIF (General)
hirotaka.yuzurihara - 16:22 Monday 02 June 2025 (34025) Print this report
lockloss investigation: 2025/05/29~06/01

I performed the lockloss investigation for the recent lockloss from the OBSERVATION state of the LSC_LOCK guardian, between 2025-05-29 05:25:11.812500 UTC and 2025-06-01 23:51:51.187500 UTC. The previous lockloss investigation was posted in klog33953. During this period, there were 31 lockloss. Note that I included the lockloss from the 'WORKING_WITH_OBSERVATION_WITHOUT_LINES', so some of the lockloss might be related to the commissioning work.

1~10Hz 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 caused the IMC lockloss. The plots are listed in DAC wiki.

One lockloss (2025-05-29 05:25:11.812500 UTC) is clearly overlapped with the planned blasting time, as shown in Figure 1. For others, I'm not sure these locklosses were triggered by the blasting, because I don't know the actual blasting time.

Oscillation of ETMY MN oplev sum

I saw the oscillation of ETMY MN oplev sum three times, as shown in Figures 2~4. In the recent lockloss study, I checked the ETMY MN oplev sum every time. But, I recognized this for the first time....
Note that the ETMY MN oplev glitch issue was reported in klog27465, but the appearance of the glitch seems to be different.
I'm not confident whether these phenomena caused the lockloss or not. As I chatted with Ushiba-san, his comment was negative regarding the relationship between this oscillation and the lockloss.

Drift of the alignment?

For 6 lockloss, the DHARD_P feedback signal shows a large value and a sudden excess of OMMT2 TRANS. This occurred at approximately -10 to -5 seconds before the lock loss. Figures 5~6 show the example. The BPC control, which was reported in klog34016 might introduce the drift of the alignment? I will check the locked data after the modification of the BPC for ETMY pitch (Fig).

Oscillation of AS17

Although this might be the commissioning work, the AS17 started to oscillate at -1 min before the lockloss, as shown in Figure 7.

Oscillation of IMC length control with 4.25 Hz

There was no excess on the seismic motion. But, the IMC length control started to oscillate with 4.25 Hz. Figure 8 shows the timeseries.

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