We'd like to retune LSC feedforward after yesterday's big alignment shift, but before doing that we want to phase POP45 and retune the LSC input matrix element that cancels PRCL in the SRCL signal.

Injecting a PRCL signal and trying to minimize the signal in POP 45 Q suggests that we need to change our phase from 8 degrees to 12 (similar to last week's conclusion that we needed to move to 11 deg). The decoupling of PRCL from Q is not as effective as it was last Friday  The second attachment shows that I checked the OLGs of MICH and SRCL before and after, and as expected they don't change much.\

After this phasing, the transfer function from POP45I/ POP 9I measured with a PRCL excitation is -0.03192.  This means that POP 9I to SRCL input matrix element should be 0.1185 = (-3.712*-0.003192)  The third screenshot shows the PRCL to SRCL transfer function before this change in blue, and after in red, so this reduced the PRCL signal in the SRCL error signal by more than a factor of 10.

After this I looked at some coherences during no SQZ time, we do still have LSC coherence at a similar level as last night, but not worse than in Jennie W's plot from last night.  Camilla is now running measurements that can be used to fit LSC feedforward.  We will leave these settings in place for tonight since it's not making things worse, and hopefully try new feedforward filters in the morning.  I've added the new POP9I to SRCl elemement in lscparams, and accepted the phase change in OBSERVE.snap and safe.snap