Jennie W, Jenne, Keita, Sheila

Summary: The input alignment was changed due to the PMC (pre-mode cleaner) swap last week. Sheila et. al. tried to recover this with IM3 moves but the IM4 TRANS QPD, our main alignment reference into the main IFO, is still off in yaw and so we will need to walk mirror or mirrors in the IMC (input mode cleaner) tomorrow to recover this.

The other option is to move something upstream in the PSL but this is harder to do as it involves moving in air steering mirrors and so is harder to reverse. This is plan B for another maintenance Tuesday.

Attached you can see how the MC mirrors changed before (first cursor) and after (second cursor) the PMC swap and Jenne tweaking the periscope mirror (first two plots in bottom row show positioning into IMC via the pitch and yaw of the upper PSL periscope mirror).

Plan: Move MC3 in yaw in order to change the output spot position in the IMC. We will do this with the ASC for the IMC running so the alignment loops for the angle of MC2 and the differential yaw between MC1 and MC3 will still run, but I will increase the gain value of these loops to its old value from December 2014 (0.25).

For future reference, the triangular cavity DOFs are discussed here: DCC LIGO-P1000135

And the MC in particular here: DCC LIGO-G1301131