This is an update on my investigation into alignment of HAM2 SEI and the alignment of the IMs on HAM2, both when the chamber is vented and when under vacuum.

In May 2017, the IM optics were aligned and damped during the vent, and the ISI was in it's nominal state before the vent, and briefly when the chamber was vented, while the IMs were still aligned and damped. 

Using the numbers from that vent, I calculated the largest alignment change in IM optics, 160urad for pitch, 108urad for yaw, and the total change in the HAM2 optical table alignment, 15urad.

For vented alignment, with doors off, and a level and centered beam through the IO optics, I used the SEI and IM alignment data from the 2014 vent when Kiwamu aligned and recorded the IM alignments in the alog. 

For current alignment under vacuum I used the alignment in May 2017, when I did an IMC beam spot measurement.

Using the vented 2014 data and under-vacuum data from May 2017, the change in the SEI (HEPI + ISI) is 142urad.

I set the maximum expected change due to SEI equal to 300urad (~SEI change * 2).

In May 2017 the IMC beam centering was measured, and found to be off-center on MC3 by -5.7mm in yaw, and from this I calculated that the beam on IM1 was -6.6mm off-center in yaw.

I calculate the position and angle changes of the beam on CW1 of the IO Faraday, and the position results from my Matlab code are shown in the table below:

The measured off-center beam on MC3 is consistent with the loss of the IMC Trans beam. My diagram showing this, is in my alog 36408.

Some changes to IM1 and IM2 alignment have been made since May, however those changes are small compared to what would be required to recover a centered beam on the IO Faraday.  From the May alignment values for IM1 and IM2, a single change of IM1 yaw of 4050urad, or a single change on IM2 yaw of 22500urad would bring the CW1 beam back to within 1mm of center.  Both changes are significantly larger than the changes measured in SEI or IMs.