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hirotaka.yuzurihara - 16:48 Tuesday 21 January 2025 (32409) Print this report
lockloss investigation: 2024/12/21~12/30

[Yong-Xiang Yang, Chia-Hsuan Hsiung, Gui Chin Liu (from Tamkang university), Chia-Jui Chou, Yuzurihara]

We started the lockloss investigation during the end-year holiday, with powerful supporters from Taiwan. We checked the timeseries by using ndscope and time-frequency map by using the Pastavi.

Details

  • This is a continuous work of klog. So, we focused on the lockloss during 2024/12/21~12/30.
  • The generated plots were collected on wiki.

 

OMC saturation

We found the OMC saturation was happening only on 2024/12/29. (Fig) (Fig) Times are below:

  • 2024-12-29 21:19:16 UTC (lock duration=151 s, saturation duration=32s)
  • 2024-12-29 19:41:26 UTC (lock duration = 193 s, saturating duration = 58 s)
  • 2024-12-29 19:04:37 UTC (lock duration = 702 s, saturating duration = 600 s)
  • 2024-12-29 17:26:56 UTC (lock duration = 278 s, saturating duration = 100 s)

The frequency of the oscillation is ~5 Hz or ~5.2 Hz. (Fig) Even though the OMC saturation was happening, the interferometer kept the locking. Is that health?

 

Excess at f<=10 Hz in PRCL and MICH

Sometimes we observed the excess at ~10 Hz in error or feedback signals of PRCL and MICH, ~30 seconds before the lockloss. (Fig) For example. 2024-12-30 21:38:25 UTC.
Possible scenario is to feedback this excess to the PRM(?). We will check more data and discuss with the interferometer experts.
It's difficult to see this excess in the timeseries. We started to collect more statistics by checking the time-frequency map. We will collect more statistics abour this phenomena.

Related to this, I prepared the script to pass the lockloss time to Pastavi web page.

  • Usage
    • /users/yuzu/lockloss/open_Pastavi.sh 481

 

Drift by BPC feedback control

Sometimes we observed the sudden drift by the BPC feedback control. (Fig) In this case, after the sudden drift, the ETMX overflow happened.
We will collect more statistics abour this phenomena.

 

ETMY MN oplev glitch

We checked the coincident lockloss with the ETMY MN oplev glitch, since 2024-12-28 12:24:50 UTC. After 12/28 13:05, there is no coincident lockloss with the ETMY MN oplev glitch. Three coincident lockloss are:

  • 2024-12-28 13:05:36 UTC (Fig)
  • 2024-12-28 12:24:50 UTC (Fig)
  • 2024-12-28 10:59:28 UTC (Fig)
Images attached to this report
Comments to this report:
hirotaka.yuzurihara - 17:00 Thursday 23 January 2025 (32431) Print this report

This is a continuous work.

Excess at f<=10 Hz in PRCL and MICH

We checked the lockloss at the time we observed the excess power in PRCL and MICH channels at f<10Hz. After the investigation, this phenomena happened only three times. The situation of each losk is different each other.

  • 2024-12-30 21:38:25 UTC
    • ETMX yaw was oscillating with ~1.7Hz. (Fig) But this is not critical for locklos. At 21 s before the lockloss, the amplitude of the ETMX yaw started to increase. (Fig) At the same time, the ASC controls started to oscilation. This will be the cause of the lockloss. (Fig)
  • For other two times, we are still not sure the clear lockloss cause.
    • 2024-12-29 22:28:25 UTC (Fig)
    • 2024-12-19 00:30:11 UTC (Fig)
Images attached to this comment
hirotaka.yuzurihara - 17:49 Thursday 23 January 2025 (32439) Print this report

[Yong-Xiang Yang, Chia-Hsuan Hsiung, Gui Chin Liu (from Tamkang university), Chia-Jui Chou, Yuzurihara]

Transient behavior by BPC feedback control

Sometimes, we observed the transient behavior in the error and feedback signal of BPC for ITMX/ETMX/ITMY/ETMY at the same time.
The error signal is computed from the K1:LSC-DARM_IN1_DQ by demodulation of 865Hz for ITMX and ETMX, 845 Hz for ITMY and ETMY, and 870 Hz. If some additional noise was induced in K1:LSC-DARM_IN1_DQ, it’s possible to mimic the shift of the beam spot and the feedback signal will be sent to the suspension and makes the drift to somewhere, even though the actual beam spot was not moved. That's the scenario we are considering.

The timeseries of error and feedback signal for the BPC are attached. You can see the transient behabior before the lockloss.
The whitened spectrogram is also attached. Before the locklos, the noise level seems to be increased due to some reason.
Based on the chat with Ushiba-san, the amount of feedback signal to ITMX/ETMX/ITMY/ETMY looks small to move the mirror drastically and make the lockloss. On ther other hand, the feedback to PRM is in the unit of urad. It's pottential to move the mirror a lot and make the lockloss.

  • 2024-12-29 22:58:28 UTC (Fig): Whitened Spectrogram around the BPC frequency (Fig)
  • 2024-12-29 22:39:37 UTC (Fig): Whitened Spectrogram around the BPC frequency (Fig)
  • 2024-12-29 19:41:26 UTC (Fig): Whitened Spectrogram around the BPC frequency (Fig)
  • 2024-12-29 19:04:37 UTC (Fig)
  • 2024-12-29 17:26:56 UTC (Fig)
  • 2024-12-28 20:36:31 UTC (Fig)
  • 2024-12-28 18:29:54 UTC (Fig)

Next step

  • Check the behavior of POP90 before the lockloss and check if the POP90 decreased by PRM feedback or not.
  • Check the spectrum of all frequency range of K1:LSC-DARM_IN1_DQ by changing the time
  • Check more lockloss time about whether this phenomena was happening or not
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