Jenne, Varun

We wanted to see if the OMC-ASC loop could be closed using the OMC dithers.

• We observed that the OMC dither error signals did not have zero crossings. Therefore, we decided to walk the error signals by tweaking the QPD offsets.
• We walked the OMC-ASC QPD offsets for PIT and YAW on QPDs A and B. We were monitoring the Optical gain and the error signals during this walk. In the end, we restored the QPD offsets where the optical gain was maximum.
• After the walk we switched from QPD error signal to Dither as follows:
  • We first ramped the MASTER-GAIN down from 0.02 to 0.
  • Next, we flipped the H1:OMC-ASC_QDSLIDER to switch to the dither error signal.
  • Lastly we ramped up the MASTER-GAIN to 0.03 at 1304969935.
• However, as the OMC dither ramped up we lost some of the optical gain we gained by walking the QPD offsets. The H1:CAL-CS_TDEP_KAPPA_C_OUTPUT went from ~1.025 to ~1.005.

In summary, we were trying to move the QPDs to zero the dither error signals, so that we could try transitioning to the dither. But, we saw that the place that had zero crossings for the dither error signals wasn't the best optical gain. We tried anyway to go to the dithers, just in case our walk wasn't the right combination of offsets to get zero crossings and good optical gain. However engaing the dither error signals resulted in the optical gain went down. Therefore, we decided to move the back to the QPDs for the higher optical gain, which is more important.