In relation to Sheila's investigation on the increased noise in the aux length loops, I ran BruCO on the loop error signals LSC-PRCL_IN1, LSC-SRCL_IN1, LSC-MICH_IN1.

PRCL

The BruCo report can be found here:

https://ldas-jobs.ligo.caltech.edu/~gabriele.vajente/bruco_prcl_1159781057/

Beside some expected coherences, there are quite some ASC signals that are coherent in the 10 to 100 Hz region. Of course, it might as well be that the angular signals are polluted by the LSC control.

• ASC-PRC1_P (fig 1) below 70 Hz
• ASC-AS_B_RF45_Q_YAW (fig 2) mostly between 20 and 40 Hz
• ASC-REFL_A_RF9_I_PIT (fig 3) is similar to the previous one, but it also shows some more coherence at the jitter peaks
• ASC-REFL_A_RF45_I_YAW (fig 4) mostly above 30 Hz and up to 100 Hz
• In addition there is some interesting coherence with input beam pointing loops and IMC WFS (fig 5, 6 and 7). In particular the IMC WFS signal shows a lot of coherence everywhere between 10 and 1000 Hz, including the jitter peaks
• Finally, there is good coherence with ASC-POP_X_RF_I_SUM (fig 8), but I'm not sure what this signal is