[JeffK, Jenne]
After Jeff noted that last night's lock had a somewhat low optical gain (kappa_C value of ~0.93), we moved the offsets in the OMC ASC QPDs to try to maximize optical gain. The attachment shows the moving that we did. It's possible that we could get a bit more if we were able to move in the direction that saturates the OMC SUS, but I'm not 100% sure about that, and to get it we'd have to pico the AS WFS so that we can move OM1 and OM2 to offload some of the alignment move.
We were able to convice the optical gain to come back to a value of 0.96ish, which is closer to what we've been having at 37W injected power for the last several weeks of O3. The offsets aren't very different from what they had been - for the most part the optical gain was happier where the alignment had been.
@DetChar -- This change in OMC alignment position appears to coincide with the drastic increase in glitches (below ~15 Hz, as reported by DMT Omega and Omicron) since Aug 1 2019.
You can confirm this by looking at trends of offsets in the OMC ASC system, under
H1:OMC-ASC_QPD_A_PIT_OFFSET
H1:OMC-ASC_QPD_A_YAW_OFFSET
H1:OMC-ASC_QPD_B_PIT_OFFSET
H1:OMC-ASC_QPD_B_YAW_OFFSET
We had changed these offsets to increase the DARM optical gain, but at the time we'd not considered that this position may be worse for things like coupling of seismic / acoustic noise, alignment jitter, scattered light, etc.
We'll bring this up at today's commissioning meeting and see if we can address it *and* improve the optical gain.