Sheila D, Elenna C, TJ S

Yesterday we ran the a2l_min_multi.py script and then Elenna adjusted the ITM yaw gains by hand to see if the script was actually helping our coupling in a way we would like (alog79904). Today, we did a similar exercise but made some adjustments to the script to see if we could tune it a bit better and get it work properly. The short answer is that the script stills seems to want the ITMY Y gain to be ~0.2 different compared to where Elenna found the best CHARD Y coherence. Other quads and dofs seemed to be ok in this instance though.

This morning we were curious if the script agreed with the changes made yesterday, so we quickly ran it at the start of commissioning. Sheila and Elenna noticed that the script didn't actually have a zero crossing for a few of the dofs, ITMY was particularly far off (seen in <a href="https://alog.ligo-wa.caltech.edu/aLOG/uploads/79921_20240905113858_a2l_demod_3_tries.png">attachment 2</a>). When the script doesn't find a zero crossing within its scan range, it would just return the initial gain and stop. So, Sheila and I made some changes by hand using a pen to screen linear fit, then ran the script again. This was better but ITMY Y didn't change because the magnitude of the gain change was greater than the gain change threshold coded in. We bumped this up from 0.2 to 0.5 and tried one more time. This try had only ITMY Y gain appreciably change, and all other dofs looked much better from a perspective of all of their demod signals had zero crossings in the center of their scan range.

At this point, the script wants ITMY Y at -2.46. Elenna then moved ITM Y gains by hand and found that the previous value (from the second running of the script) of -2.2 for ITMY Y looked best. See attachment 1. The -2.46 gain looked worse <20Hz, see the top right plot in the attached. Elenna also checked DHARD and agreed that it looks good.

We aren't really sure why the script disagrees so much with this one dof right now. This script is based on one that LLO uses, and it seems to work for them. More thought needed.

Initial a2l gains before starting this morning:

            'P2L':{'ITMX':-0.98,
                   'ITMY':-0.36,
                   'ETMX':3.08,
                   'ETMY':4.48},
            'Y2L':{'ITMX':2.90,
                   'ITMY':-1.7,
                   'ETMX':4.85,
                   'ETMY':1.13 },

Final a2l gains:
            'P2L':{'ITMX':-1.0,
                   'ITMY':-0.39,
                   'ETMX':2.98,
                   'ETMY':4.72},
            'Y2L':{'ITMX':2.87,
                   'ITMY':-2.25,
                   'ETMX':4.88,
                   'ETMY':1.49 },