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hirotaka.yuzurihara - 15:51 Wednesday 19 March 2025 (33036) Print this report
lockloss investigation: 2025/03/19 UTC

[Obayashi (Aogaku), Yuzurihara]
We started the lockloss investigation on 2025/03/18 4:34 UTC ~ 3/19 5:08 UTC, with powerful supporters from Aogaku. Previous lockloss investigation was posted in klog32903.
During this period, there were 7 lockloss. The phenomena before the lockloss are almost same as the previous (3/5).

1Hz seismic motion made the IMC lockloss

The excess of the seismic motion with 1~10 Hz made the oscillation of the IMC length control and made the IMC lockloss.

  • 2025-03-18 12:56:57.562500 UTC (3921 s) [Fig]
  • 2025-03-19 00:28:32.187500 UTC (9048 s) [Fig] [Fig]

OMC PD saturation with 35~40 Hz

This phenoemnon is same as previous. The frequency of the oscillation are not aways 40 Hz, sometimes 35 Hz.

  • 2025-03-18 04:43:04.312500 UTC (174 s)
  • 2025-03-19 01:28:45.937500 UTC (1930 s) [Fig]
  • 2025-03-19 02:12:34.937500 UTC (737 s) [Fig]
    • Just memo: the IRX and IRY were oscillated with 0.88 Hz. The coincident oscillation can be seen in DHARD-Y, DSOFT-Y, ITMX-Y, and ETMX-Y. [Fig]
  • 2025-03-19 05:08:52.062500 UTC (32 s)

OMC PD oscillation and increasing amplitude with 53 Hz (New !!)

This is a new phenomena. We observed the amplitude of OMC PD was increasing with 53 Hz. We tried to investigate the coincident signals. But, there was no clue.

  • 2025-03-18 13:45:33.187500 UTC (1919 s) [Fig]
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Comments to this report:
hirotaka.yuzurihara - 16:18 Wednesday 19 March 2025 (33038) Print this report

[Kenta, Komori, Obayashi, Yuzurihara]
Related to OMC PD saturation, we found that interesting phenomena.
Although there was the oscillation of K1:OMC-TRANS_DC_A_IN1_DQ with 40 Hz, the lockloss was not occurred. [Fig] [Fig]
Initially we thought that this 40 Hz oscillation was caused by the resonance kick of the Type-A suspension. If so, the decay time of the oscillation should be longer more. So, the OMC PD oscillation seems not to be related to the resonance kick.

Note that

  • IR power reduction occurred with the coincidence of the OMC PD oscillation. The magnitude of AS17 seens to be not bad, in both cases.
  • The lockloss occured at 30 s or 5 s after this oscillation happened.
  • A possible hypothesis of this lockloss is that the optical gain changes with time, the unity gain frequency drops to ~40 Hz, and DARM control failed. Is there any way to monitor the optical gain? pcal line?
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