Jennie, Matt Todd, Craig
TL;DR We restored the alignment from O4a onto the ISS QPD array and IM4 Trans by moving IM1 and IM3
This has recovered the full-lock input-on-the-PRM power from 54.5 W to 57.5 W.
We are probably in a spot where we can trust Keita's IM4 TRANS calibration from alog 62213 again,
meaning we can trust our PRG of 50 W/W.
History
I tried doing this yesterday (alog 76291), but we were worried about changing the input alignment while not in lock.
Later, Sheila tried picoing onto the ISS Array (alog 76303), but undid her changes when they were causing us to fall off the array.
Alignment
Loosely, we wanted to restore the alignment we had at the end of O4a.
Centering on the ISS QPD is not necessarily the best for the alignment onto the actual ISS Array.
Additionally, the ISS QPD dofs are flipped (PIT is YAW, YAW is PIT).
I started moving IM3 and IM4 in conjunction to center the QPDs, but this didn't work because we were moving too much on the ISS QPD and not really moving on IM4 TRANS, to the point where we were falling off the diodes in the array.
So after that, I started moving IM1 and IM3 with much better results, pitching up with IM1 onto IM4 TRANS, then recovering the ISS QPD with pitching down IM3.
We ended up at the below alignments:
Epoch GPStime Sensor Pitch Yaw
---------------------------------------------------------
O4a 1389013541 ISS QPD -0.62 0.72
IM4 TRANS -0.44 -0.34
Pre-O4b 1394409800 ISS QPD -0.54 0.75
IM4 TRANS -0.02 -0.20
This afternoon, our high frequency DARM, above 4kHz, improved. Plot attached. This was during these IM moves, also had we swapped to the NEW_DARM configuration (so low frequency calibration is incorrect) and had moved the OMC 76335 this AM.
This high frequency DARM then again increased with seemingly no IFO changes. Using the aligoNB ISS_excitation_LF.xml template with no excitation, we could show that there is high coherence between DARM and the 2nd loop ISS: plot.
It looks like the alignment on LSC_POP changed or started clipping during this IM move. This morning TJ is reverting the IMs, (and PR3), before starting an initial alignment.
Here are some extra trends during the in-lock input beam walking yesterday.
- Top two rows are IM1 and IM3 PIT and YAW
- 3rd and 4th rows are IM4 and PRM driftmons as they follow the changes to IM1 and IM3
- Below that is IM4_TRANS, the ISS QPD, ASC-POP_A, ASC-POP_B, LSC-POP, LSC-REFL and AS_C.
The cursors are where the beams were during the last lock of O4a.
There is a lot of plots so the second and third attachments are just the same plots but zoomed in to the SUS alignments, and the PD signals.
- If the driftmons are calibrated into microradians, PRM was pitched 230 urad.
- While stepping the alignment we ended up at the O4a spot position in PIT according to the ISS QPD, but
- Both IM4_TRANS_PIT and ASC-POP_B_PIT started low and ended above their O4a positions
- ASC-POP_A_PIT started close to its O4a position and ended well above
- While stepping the alignment we wended up at the O4a spot position in YAW according to the ISS QPD, but
- IM4_TRANS_YAW started high and got higher (the cursor for O4a reference is off the screen at -0.35), ASC-POP_A_YAW started low and ended lower, ASC-POP_B_YAW started low and ended lower.
- As for the LSC diodes: LSC-POP ended up pretty close but a little lower than where we started, and LSC-REFL also ended lower. AS_C went up very slightly
