Summary:

HAM2 moved by about -10 to -8 urad in YAW (in SUS coordinates) and some unknown angle in PIT. This was apparently triggered by the maintenance work for HEPI. Even though Hugh had to back off all the changes due to some other problem they have found, and made sure that SEI sensors are brought back to the original readings, ISI never went back to its original angle.

This is not the first time HEPI or ISI apparently moved though SEI sensors told otherwise.

Details:

In the attached, all plots start before the maintenance and end right when HAM2 was brought back to the old SEI sensor readings. Also, at the end of the plot, MC WFS was engaged.

In CH3 and CH4, you can see that the HAM2 ISI OPLEV saw some big change both in PIT and YAW. The numbers, especially YAW, cannot be trusted too much as the beam is almost all in the right half of the quad diode and nobody took time to confirm the calibration/sign, you can still assert that the ISI angle is totally different from where it used to be.

According to PR3 oplev (CH1 and 2) the HAM2 ISI oplev data in that ISI moved -10 urad in YAW. The optic moved by +4 urad in PIT but this doesn't mean that the ISI moved by this amount.

Other optics on HAM2 are without oplev and therefore don't have an independent measure of the angle external to ISI, but you can see small changes in the OSEMs.

In addition, after the MC locked and the WFS brought the alignment to wherever it thought was good, all MC mirrors settled to different OSEM readings than the original. This means that MC mirrors are sitting at different angles relative to the ISI.

Anyway, the AS beam was at a totally wrong location and we were worried that our alignment was completely wrong, because there's apparently a centering servo for IM4 transmission acting on PZT mirror, but in the end twisting PR3 back by +8 urad in YAW and -2urad in PIT seemed to take care of most of the bad things.

I confirmed that these shifts in optics on HAM2 are NOT due to the bias slider or IFO ASC.