During the work, we temporarily activated the resonant gain (resG) filter in FM9 of K1:OMC-LSC_FB_FLT, which was previously unused, to mitigate the 9 Hz peak in the OMC LSC error signal caused by nearby construction activities. While this action effectively suppressed the 9 Hz peak, it introduced a gain peaking around 10 Hz, indicating a lack of phase margin at this frequency. Consequently, we deactivated the filter.

Additionally, we temporarily added a 3 dB gain in FM5 of K1:ASC-PRC2_P, which was also previously unused, to address PR3 fluctuations. During offset tuning, the DARM spectrum got worse, and PR3 fluctuations appeared slightly larger than usual. Although increasing the ASC gain successfully suppressed the fluctuations, the DARM spectrum remained unchanged. Therefore, we have deactivated the gain filter.