This is the additional report about the Transient behavior by BPC feedback control. These lockloss looks to be related to the 5 Hz oscillation of K1:LSC-OMC_DC_OUT_DQ and K1:ASC-DHARD_{P, Y}_IN1_DQ. But, I'm not sure the origin of the 5Hz oscillation.
The common features for these locklosses
I checked the data around the lockloss time listed in the previous post (klog).
- K1:LSC-OMC_DC_OUT_DQ was oscillating with the 5~5.25Hz during the LSC_LOCK guardian was in OBSERVATION_WITHOUT_LINES state. Its amplitude was growing. (Fig) (Fig)
- K1:ASC-DHARD_P_IN1_DQ and K1:ASC-DHARD_Y_IN1_DQ shows the same oscillation. The amplitude was not growing. (Fig) The timing of the peaks between these ASC channels looks different.
- I checked the oplev signals related to Xarm and Yarm. There was no channels with clear 5 Hz oscillation.
- At 10~20s before the lockloss, the BPC error and feedback signals shows the transient behavior. This phenomena was reported in the previous post (klog). As we checked the ~100 locklosses, this phenomena happened only just before the lockloss.
[homework]Check the behavior of POP90 before the lockloss
We checked the POP90 before the lockloss. But, we could not find the coincident behavior between POP90 and BPC feedback. (Fig)
[homework]Check the spectrum of all frequency range of K1:LSC-DARM_IN1_DQ
I compared the spectrum just before the lockloss (Fig) and the spectrum of 4 minutes before the lockloss (Fig). Due to the 5Hz oscillation, the spectrum shape looks different. But, this different shape continues for more than 1 minutes. I'm not sure why the BPC feedback was affected by the oscillation only just before the lockloss.
For other 6 lockloss, we observed similar behavior.
Discussion
I discussed the possible cause of 5 Hz oscillation with Kenta-san, Yokozawa-san, and Washimi-san.
- Although we doubted the water release from dam, the seismometer shows the different behavior.
- I found the 3~10Hz BLRMS of the seismometer was increased between 18:00 UTC~22:00 UTC. (12/28) (12/29) These time is 3:00~7:00 JST.
- Yokozawa-san commented the possibility that the snow-removing vehicle was working around the KAGRA site. I checked the snow condition at 12/28 and 12/29. The information at Takayama are available (12/28) (12/29). But, I couldn't find the information at KAGRA site. Based on these pages, the weather at Takayama was snow.
- Or I should ask the people at snow-removing center?
- Idea of contamination path
- [cause] snow-removing center --> [cause/phenomena] 5 Hz oscillation at OMC PD and ASC control --> [phenomena] BPC feedback --> lockloss
