Jeff, Sheila, Elenna
Executive summary: Our input alignment has changed. We know this because the alignment onto IM4 trans has changed. This corresponds to the IMs 1-3 OSEMs showing a change, which corresponds with HAM2 being taken offline to change the power supply.
Today, an H1SEI23 power supply was replaced, and preceding this activity HAM2 and HAM3 were taken offline, 85475.
When HAM2 came back online, the OSEM readbacks on IMs 1-3 showed a change in both pitch and yaw. The table below summarizes how much each suspension's alignment has changed.
| IM | Pit change (urad) | Yaw change (urad) |
| 1 | 2 | 0 |
| 2 | 66.8 | 2.7 |
| 3 | 14.8 | 4.3 |
This shift in alignment is also apparent on IM4 trans, which shows the pitch offset has increased by 0.3 and yaw offset by 0.03 (uncalibrated).
We first noticed something had changed when we ran input alignment- I had to move PR2 by 5 microradians in both pitch and yaw just to get the lock to catch, and then the alignment offload further changed the PR2 sliders.
This change is further backed up by the fact that the POP A offsets have changed, and the PRG at 2 W seems to have decreased slightly.
We're not sure how bad of a problem this is. We have been able to lock and power up with no issues. We had a random unrelated lockloss, so I cannot yet see if the buildups at full power once thermalized have changed significantly.
The locking process is now much slower again, since the alignment offsets for the PRM have changed, and the convergence of the PRM ADS tends to set the rate at which we can engage ASC in full lock.
The first two attachments are screenshots show the shift in the IM alignment and IM4 trans alignment. I included the HAM2 ISI guardian state to show this change corresponds with HAM2 going offline.
The third attachment shows how the POP A offset has changed at full IFO 2 W. We can use this scope to adjust the POP A QPD offset and speed up locking, if we want to keep this input alignment.
The fourth attachment shows the ITMX green camera offset screen in full IFO at 2 W. I was watching this screen to confirm the new ITMX green camera offsets I set earlier today were ok. I think the set value differs from the live value here because of the new input alignment.
We sat at full power for 1 hour and had thermalized to a PRG of 49. Trending back to our last lock before maintenance it looks like we achieve about the same PRG in this amount of time, so there is minimal impact on the buildups. There might be a small reduction in the jitter coupling. We should check again when fully thermalized to be sure.
Since we are going to stay this way for at least tonight, I updated the POP A offsets to help shorten ENGAGE ASC FOR FULL IFO. SDF attached.
