I have engaged the new damping loops for SRM, SR2, PRM and PR2 and we have acquired DRMI lock with no issues. See alog 65310 for a reminder of the work done by Jeff K and me regarding installing these loops.

There was a ~3.3 Hz oscillation in the ASC loops (CHARD and CSOFT P) when we engaged the ASC for full IFO. I spent some time reducing the gain of PRC2 P and measuring the loop. Even though the oscillations were visible in the arm loops, we have had 3 Hz instabilities in PRC2 P in the past, so I was immediately suspicious given the HSTS damping change. When I made a quick OLTF measurement of PRC2 P, there was gain peaking present in the loop at 3.3 Hz, but the gain reduction didn't make a difference. I then spent some time reminding myself of PRC2 P ASC loop changes I had made in the past (alog 64523) that attempted to reduce the gain peaking at this frequency. I ended up reverting to the older PR2 plant inversion in FM7. Then I was able to bring the gain back up to nominal.

It may be that best practice is to use FM8 in PRC2 P for DRMI acquisition, and then FM7 for full lock. I will update the guardian with this configuration for now, and then we can watch and see if this scheme needs further adjustment. The switch from FM7 to FM8 was prompted by 3 Hz ringing during DRMI acquisition back in August. I will keep an eye on this.