Sheila, Alexa, Elli, Evan, Gabriele
Because the DHARD WFS plant for pitch changes significantly with the CARM offset reduction, which we think could be caused by miscentering on the optics combined with radiation pressure. We have attempted to center the green beams on the ETMs this morning. We used the PCAL cameras and the code that Elli had been using, but did not use the fitting function, instead just looking by eye at the corsshairs that mark the center of the optic relative to the position of our beams.
For the Y arm we moved the green QPD A yaw from 0.5 (photo 100) to -0.5 (photo 105). For the X arm we ended up not moving, there are no QPD offsets on the X arm.
We found that we were not well aligned after this work, which might have been unrelated to what we did. Now we have reverted the offsets, but it woul be worth trying to put them back in at some time.
We had some suspicious alignment issues today. To align the two arms, we ran the green wfs which feeds back to the ITMs, ETMs, and TMSs, as we have been doing for several weeks now. Then we followed our input pointing, PRM aligning, MICH aligning, and SRM aligning. We could then lock IR with ALS COMM and produce a good build up in the x-arm; however, when we locked ALS DIFF, we were about 5% below the nominal IR build up in the y-arm. We kept seeing an oscillation in AS 45Q before transitioning to RF DARM, and we consistently were losing lock. DRMI was also taking longer to lock (about 12min). We were frusturated and decided to start aligning from scratch. We cleared all the WFS history, used the nominal QPD offsets as described above, and then used the baffle PDs to align the TMS. We then adjusted ITMs and ETMs by hand to get the green build up high in both the arms. This restored the IR build up in the y-arm when locked on ALS DIFF, and allowed us to reach full lock with DRMI locking on the order of minutes. For sanity check, I looked at the PCAL image in green of the Y-arm and it looked the same as above with the corresponding QPD offset (image LHOX 106). I am not sure why the green wfs took us to a "bad" alignment today; these have been reliable in the past.