KAGRA Logbook

DetChar (General)

hirotaka.yuzurihara - 14:21 Friday 06 June 2025 (34086)

Scattered light noise in MICH error and feedback channels

[Shih-Hong, Yuzurihara]

As a continuous analysis of klog34029, we checked the Gauch page and found the MICH channel shows the non-Gaussian behavior in 10~20 Hz. Figure 1 shows an example of the Gauch. This phenomenon began on 6/2 at 14:00 UTC (Gauch).

Figures 2~4 show today's sensitivity and noise projection from MICH. The spectral shape of the sensitivity around 15 Hz is similar to the MICH shape.

In the summary page, you can see the time variation of the MICH spectrum. (This shoulder-ish shape looks like the scattered light noise.)

Figure 5 shows the Q-spectrogram (by Pastavi) of the MICH error signal. This noise is a scattered light noise. By rough eye check, the frequency of the scattered object seems to be 0.2 Hz. (= ~12 period/60 s)

Yokozawa-san will report his continuous analysis.

Images attached to this report

34086_1749186542_K1-LSC-MICH_OUT_DQ_beg1432947618_time3600_int20_fft1_10_1500_pv_log.png

34086_1749186859_1433075418_1433075478_K1-LSC-MICH_IN1_DQ_Q-Transform.png

Comments to this report:

takaaki.yokozawa - 14:25 Friday 06 June 2025 (34087)

We checked several signals related with around MICH.
And I found when the oscillation of the SR2 TM Y became more than +/- 2urad, this scattered light happened as shown in Fig.1.,
The threshold(+/- 2urad) exceeded around 2nd June. and when the oscillation became relatively smaller, the scattered light noise at MICH also became smaller.
And actually, the oscillation of the SR2 yaw was about 0.2 Hz.

We don't know the noise path from SR2 to MICH scattered light, the reason of scattered light may come from the SR2 yaw oscillation.

Images attached to this comment

34087_1749187507_Screenshot from 2025-06-06 13-32-54.png

34087_1749187833_Screenshot from 2025-06-06 14-30-11.png

hirotaka.yuzurihara - 15:47 Tuesday 10 June 2025 (34136)

As I checked Gauch, thanks to the SR2 work (klog34117), the non-Gaussian feature of the frequency less than 30 Hz in the MICH channel disappeared after 6/9 18:00 JST. Figure 1 shows an example of Gauch plots.
Figures 2 and 3 show the spectrum of the MICH error signal in the 6/8 (before SR2 work) and 6/9 (after SR2 work) summary pages, respectively. The shoulder-ish structure around the 20 Hz disappeared.
Note that this noise caused trouble in the calibration line (klog32114).

In addition to this noise in the MICH, the occurrence rate of the transient noise in the PRCL feedback (reported in klog34029) seems to be reduced. Sometimes the transient noise remains. But the number is significantly reduced. I'm not sure whether the coincident transient disappeared from the strain channel or not. I will continue to monitor it.

Images attached to this comment