Naoki, Sheila, Camilla

After the output alignment shift reported in 77427, we tried to revert SQZ to the last successful SQZ-OMC scan in 77515 but when we increased throughput, AS_C alignment was bad. Today we translated the beam to get good throughput on AS_A/B and AS_C and a centered beam on AS_C with OMC DC centering loop running. This was a move of ZM4 -1000urad, ZM5 -650urad in yaw as reported by DAMP_Y_INMON channels

• We reverted all alignment sliders (ZM4,5,6 OM1,2,3 SRM) and PSAMS to April 16th (leaving PSAMS at 7.5V/0.55V pre-77268).
• Naoki injected the same amount of SQZ SEED power as previous OMC-SQZ scan
• We translated in YAW by yawing ZM5 negative 50urad to increase AS_A power and then yawing ZM4 negative to bring the beam back centered to AS_C. Tried the positive ZM5 direction beforehand and it got worse.
• At 19:49UTC we turned on the OMC DC centering loops.
• We had god throughput at 19:59UTC and  moved until we made things worse at ~20:00UTC and then backed off.
• Total ZM4,5 changes attached, sdf's attached.
  • Before 1st t-cursor is moving from optimum in-lock sqz to April 16th OMC-SQZ alignment.
  • Between t-cursors is our translation. We moved ZM4 -1000urad, ZM5 -650urad. ZM4 is at 24,000 counts out of available 32,000.

Attached shows previous April 16th OMC-SQZ scan compared to during today's translation and how we left the ZMs:

• AS_C power is similar (new 373 vs old 385). Around ~3% percent lower, it almost seemed correlated with oscillations in YAW which isn't good as could suggest some yaw clipping remains.
• AS_A/B power is similar/increased,  AS_A (new 74 vs old 75) and AS_B  (new 80 vs old 75). They were not the same as each other similar but this can be explained by the AS_C being  0.2 to 0.4 off in PIT and YAW in the April 16th scan.
• Centered on all AS_A/B/C PDs.

We're not sure how this change will effect in-lock SQZ as Vicky had to make big changed in 77400  and we may have seen that good OMC scan alignment isn't good SQZ alignment?