I have updated the SRC2 and MICH ASC controllers and cutoffs. The SRC2 P and Y controllers are the same that are applied to PRC2, with previous success (see 69108).

The MICH controllers are very different than before. I measured the MICH P olg recently and found it had a 2 Hz bandwidth, which seems high. The new controller reduces the bandwidth to 0.6 Hz. This allows us 24 dB less noise injection from 10-20 Hz. The MICH loops are now significant contributors to the ASC sub budget, so will be a significant improvement to ASC noise.

There is much more 0.5 Hz motion in the MICH P loop with this new controller engaged. The new loop has 16 dB of gain margin, so I increased the gain by 6 dB. There is still more 0.5 Hz motion than we are used to in MICH. It is not unstable. I will look into adjusting this loop design so we can improve the suppression at 0.5 Hz further but maintain some of the improved cutoff at 10 Hz. The MICH Y loop looks fine, although it also shows increased low frequency RMS.

All of these controllers are now guardianized. SRC2 is engaged in ENGAGE_ASC with the new controller and cutoff. The MICH loop is turned off briefly in OFFLOAD_DRMI to switch from AS 45 to AS 36, so I use that moment to switch over to the new controller and cutoff. I then increase the MICH P gain in PREP ASC to further suppress the 0.5 Hz motion.

In MICH P, FM7 now replaces FM8 and 10. In MICH Y, FM5 replaces FM7 and FM10. IN SRC2 P and Y, FM6 replaces FM7 and 9.

There is possibly small improvement in DARM between 10-20 Hz, but with all the other changes today, it is hard to tell.