[Keita, Sheila, Daniel, Jenne]
Keita pointed out to me that the ITM a2l gains have been moving monotonically in yaw for the last month or two. I ran the script to figure out what this means for spot positions, and it looks like the spots on the ITMs have moved about 3mm in yaw since the 20th of November.
We may investigate trying to move the spots back toward their Nov/Dec values, in hopes that that will alleviate the noise that we've been seeing the last few days.
Jenne, Sheila
We have tried the three things described in alog 33230:
We saw that the MICH to DARM coupling hasn't changed since measurements made in November, the SRCL to DARM noise coupling is worse by about 5dB, so our feedforward was slightly mistuned, but this the projection of this noise is still about a factor of 5 below the DARM noise, and the PRCL coupling has gotten a few dB better (but this noise is not important).
We moved PRM yaw by about 45 urad, which brings our spot position on the POP A QPD close to centered, and brings us much closer to centered on the ITMs. We first thought that this helped, but it wasn't repeatable, so we have reverted. We also tried opening the SRM loop and moving SRM, but this made no repeatable difference.