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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