1. ALSX is not healthy yet
Slow servo to ETMX (tidal) doesn't work yet. The feedback signal actually pushes the ETMX. I can see that the oplev moves by as large as 1urad or so when tidal into L1 is active but I don't know if that's the reason why ALSX loses lock as soon as slow is enabled. Ryan confirmed that the L2A gains/filters didn't seem to have changed recently.
I tried turning on green WFS (but not camera) without slow servo by going to ENABLE_WFS and turning off camera servo manually. That resulted in a slow 1.6Hz oscillation. I gave up after failing twice.
2. It seems that POP beam needs to be moved in +Y direction on HAM1/HAM2 septum
Not everything makes sense but it seems that POP beam needs to be steered in +Y direction on HAM1HAM2 septum (-X direction in ISCT1).
I looked at the single bounce beam from ITMX at 60W in ISCT1 and the beam seemed to be shifted too much in +X direction on ICST1 top periscope mirror compared with how I set the path up when ISCT1 was open. See POP_beam_too_much_to_the_left.jpg.
I quickly moved the POP beam in HAM1 using just PR3 angle as a quick and dirty method. I used POP_X_SUM as the power monitor for the single bounce beam in HAM1. I used PM1 to center POP_X. Without centering, when the beam is close to the center, a change in the beam position will result in a meaningful increase of power due to the center gap between the PD elements. If the beam is entirely in one quadrant this isn't an issue but it's difficult to know if that's the case when you're intentionally moving the beam.
I moved PR3 YAW from -236.7 to -245.7urad (PIT wasn't moved) and used PM1 to compensate. As the beam moved, at first the power didn't seem to change much if at all, but eventually it increased from 42 counts to 48 counts. This was pretty repeatable. I couldn't move PR3 further as PM1 railed. See POP_X_SUM_increase.png and POP_beam_after_PR3_move.jpg.
After moving PR3 I lost the beam on POP_A completely but that wasn't surprising. Even before moving PR3, by scanning PM1 I saw that the beam was not centered on POP_A when POP_X was centered. (The POP_X and POP_A see the same beam coming through the 334mm lens, but the distances from the lens to POP_X and POP_A are about 390mm and 310mm according to my eyeballing D1000313. That's large enough of a difference. If for example the beam position on PM1 changes by 5mm and you use PM1 to center the beam on POP_X, the beam position shifts by ~1mm on POP_A, that's already the radius of POP_A PD.)
After this excercise I moved PR3 and PM1 back to where they were before I started.
Not sure if we're ready to use pico in HAM3 yet as not everything seems to make sense. For example Masayuki and Sheila moved spot position on PR2 and saw no change in POP power.
3. Realigned COMM and DIFF
In the COMM path the beams were too low on the common BS and was heavily clipped. I fixed that and the COMM beat note changed from ~ -1.3 to 5.9 dBm. I changed the DIFF path too but it didn't change much.
