[Sheila, Craig, Georgia]
Summary
We had some clipping, probably in the PRC. We adjusted IM4 and now have 25% improvement in PRC buildup as measured on POPAIR_B_RF18, and 10% as measured on POPAIR_B_RF90 (compared to last night). This is still lower than we expect, but it is a step in the right direction.
Details
We checked the PRMI build-up again, locking PRX, MICH, then PRMI, and found it similar to yesterday (alog 42570).
We checked the beam on the POPAIR_B diode and found that the beam is overfilling the diode, we should install a shorter focal length lens in front of this but it is not urgent.
We then tried to check for clipping: we set the IFO for single bounce off ITMY, and made a feedback loop between AS_C and ITMY. We moved IM4 in yaw and found that we lost power straight away. We checked the AS_A and AS_B centering loops and found that we were clipping on the OFI, which we then fixed with SR2. We then tried to check for clipping again but this time using AS_A, we moved IM4 in pitch and found that the sum output of AS_A increased, which suggested clipping. To maximise the AS_A sum we had to move IM4 roughly -2000 counts in pitch (from original alignment of -400 to -2400).
Meanwhile Craig checked the spot positions on the PRC mirrors and found we were off in pitch, he'll attach his results in a comment.
We went back to aligning PRX, MICH and PRMI walking IM4, PRM, and PR2, screenshot of alignment sliders attached. We found a 25% improvement in build-up according to POPAIR_B_RF18. We re-ran Craig's spot position measurement and found we were closer to the centres of PR2 and PR3 in yaw. This is a good start. Stay tuned!
PRC mirror spot estimates after PRC A2L minimization using Hang's decoupling script and Kiwamu's HSTS and HLTS alpha to mm:
All numbers are in mm from the LL coil.
PRM P PR2 P PR3 P PRM Y PR2 Y PR3 Y
-2.4890 0.3589 -3.1097 -1.6346 17.1775 -15.8104
-2.5006 -0.2489 -2.8373 -1.5536 16.5192 -13.5315
Jenne's coil signals
Koji's alpha definition
More Kiwamu
Koji's original calculation had a small error, which Kiwamu inherited, and that overestimates the centering offset by a small amount (less than 10%).
Read Koji's log that you linked which was updated last year, update Kiwamu's calculation, attach comments to Kiwamu's entries so we don't keep repeating the same error repeatedly.
I calculated the corrections to Kiwamu's alpha to mm values, according to Koji's 2017 correction to elog 2863 Corrected HSTS and HLTS alpha to mm factors: ============================================ HSTS alpha to mm: 39.28 HLTS vertical alpha to mm: 50.93 HLTS horizontal alpha to mm: 87.43 Also attached alogs 42600 and 42601 to Kiwamu's original alogs to avoid future confusion.
New miscentering in PRC after alpha to mm factor corrections (plus additional alignment happening right now)
All numbers are in mm from the optic center using LL as the fiducial coil.
PRM P PR2 P PR3 P PRM Y PR2 Y PR3 Y
-2.7622 1.1651 -0.7635 -1.2032 15.3530 -12.3856