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MIF (General)

hirotaka.yuzurihara - 0:13 Tuesday 08 April 2025 (33288)

lockloss investigation: 2025/04/04~04/07

[Kenta, Yuzurihara]
We performed the lockloss investigation for the recent lockloss from the OBSERVATION state of the LSC_LOCK guardian, between 2025-04-05 03:54:16 UTC and 2025-04-07 05:54:54 UTC. The previous lockloss investigation was posted in klog33153.
During this period, there were 10 lockloss. The plots are summarized in wiki.

PMC HV Saturation

The 1 lockloss (2025-04-05 03:54:16 UTC) was occured because the PMC HV was saturated. Figure 1 shows the screenshot that K1:PSL-PMC_PZT_HV_MON_OUT_DQ touched the limit value (300).
During this period (4/4~4/7), the most of lockloss was occured under the the saturation of K1:PSL-PMC_HEATER_INMON (15000). Except for one lockloss, the direct lockloss cause was not related to the PMC saturation.

1Hz seismic motion made the IMC lockloss

For 2 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.

2025-04-06 06:02:46 UTC (Fig)
2025-04-07 00:53:24 UTC (Fig)

Oscillation of OMC DC PD

This phenomena was observed many times in the lockloss in March. In this period, this phenomena was observed in 1 lockloss. (2025-04-06 20:26:15 UTC), as seen in Fig 4. The cause of the oscillation was unclear.

Oscillation of OMC DCPD over 5~10 seconds

2025-04-06 02:53:10 UTC
2025-04-06 03:09:56 UTC

This new phenomena were observed in 2 lockloss. It took 5~10 secods for the OMC DCPD to oscillate and saturate, as seen Fig5 and Fig6. The oscillation frequency was 44 and 43 Hz, respectively.
As shown the figures, the OMMT2 TRANS was not increased just before the lockloss. It indicates that the laser power arriving the AS port was not increased. But, the laser power of OMC DCPD increased with 5 seconds... We need more samples....
When the OMC DCPD started to oscilalte, the power of IR trans dropped coincidently.
There was no strange behavior on AS17 (=DC OFFSET value).

Others

For 1 lockloss (2025-04-07 05:54:54 UTC), there was no hint, except for the saturation of K1:PSL-PMC_HEATER_INMON. The OMMT2 TRANS was stable.

For 3 lockloss, the excitation was underway. I will let these lockloss be.

Images attached to this report

Comments to this report:

hirotaka.yuzurihara - 11:31 Tuesday 08 April 2025 (33303)

I checked the additional 5 lockloss occurred at 4/7. The previous lockloss investigation was posted in klog33288. The plots are summarized in wiki.
One good news is that the lockloss due to the OMC saturation with 40 Hz has occurred much less frequently, thanks to the commissioners' parient work.

1Hz seismic motion made the IMC lockloss

For 2 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.

2025-04-07 10:21:44.437500 UTC (765 s) (Fig 1)
2025-04-07 15:40:13.562500 UTC (1790 s) (Fig 2)

PR2 and PRM oscillation at 0.6~0.8 Hz

For 1 lockloss (2025-04-07 19:58:49.562500 UTC), there was an oscillation in the PR2 pitch and PRM pitch with 0.6~0.8 Hz (Fig 3 and 4). It started at -30 s of the lockloss. The trigger seems to be the excess of the seismic motion. (Fig5)

Others

For 1 lockloss(2025-04-07 11:53:44.437500 UTC (4084 s)), there was less hint. The OMMT2 TRANS was stable (Fig6). I checked the BPC controls, because this lock was over one hour. The ITMX yaw and ETMX yaw seem to be drifting (Fig7) so that the error signal is away from zero. But, I'm not confident that this is the lockloss cause.
Just after this lockloss (<1s), the excess of the seismic motion was observed in 1~30Hz frequency bands. The lockloss occurred before this excess (Fig8).
At -18 min of the lockloss, there was the excess at 10~20 Hz (Fig9).

For 1 lockloss at WORKING_WITH_OBSERVATION_WITHOUT_LINES, the excitation was underway. I will let it be.

Images attached to this comment

hirotaka.yuzurihara - 11:32 Tuesday 08 April 2025 (33302)

Oscillation of OMC DCPD over 5~10 seconds

2025-04-06 02:53:10 UTC
2025-04-06 03:09:56 UTC

For these two lockloss, actually Yokozawa-san was changing the filter, as chatted with Yokozawa-san. As a result, the lockloss occurred. So, they are not new phenomena.
The LSC_LOCK guardian state was at WORKING_WITH_OBSERVATION_WITHOUT_LINES (this state was set properly). I missed this information.