HAM6 rest of the laser-related work part 1: OMC shroud problems (Naoki, Rahul, Keita)

Preparations:

ASC-AS_C was centered using SRM. It was moving more than I'd have liked but it was OK.

Confirmed that Irises on HAM6 were centered.

The laser beam was on both of OMC QPDs but sadly they were pretty off-centered. Things were swinging more than I'd have liked but anyway I roughly centered the beam on both QPDs using OM1/2/3.

	P slider (now/before)	Y slider (now/before)	DAC max now
OM1	120/90	510/610	7.3k
OM2	730/-80	760/760	10k
OM3	-1100/-550	-184/-74	14k

This means that, due to the cable rerouting/retouching we've done when we put the shroud panel on last week (alog 75651), OMC is hanging at a different angle. That's OK as far as DAC of OM1/2/3 won't saturate once we pump down.

This also means that both WFSs are not centered at all. That's OK, we can pico.

OMCR was good:

We visually checked the centering on the OMCR diode using a viewer card. It was OK in that it's not close to the edge, so we left it as is. The distance from the edge of the V-damp to the OMCR is pretty mush the same as Julian's photo from Jan/31 (alog 75653).

OMC trans video beam doesn't come out of the shroud:

I scanned the OMC PZT2 and was able to see that the DCPDs are flashing, but no beam was visible on the steering mirror of the OMC trans video beam.

We removed the +X+Y-side short shroud panel, and immediately I saw the beam, it was faint but obvious using the IR card and the viewer combined. It was already hitting the steering mirror, and the beam was roughly going to the direction of the video viewport.

Using a ruler and the IR viewer card, we found that the beam height was, very roughly, 4" from the OMCS cage to the steering mirror. Maybe it was a tad low.

Rahul placed a ruler on the ISI table to mark the rough beam position close to the +X door, see his picture.

We put on the shroud panel and the beam is gone no matter what. We even did Betsy/TJ/Fil/RichM/Peter/Koji/Calum trick (alog 28944) they did back in 2016 to move the -X-Y-side short panel around more than designed, without success.

It's very hard to find where the beam is at the panel location. Since we know where the beam is at the edge of HAM6 close to video viewport, we can use a laser pointer to back trace the beam path and see if the baffle hole should move to +X or -X direction, but that won't change the fact that we couldn't bring the beam out with the shroud panel.

Fundamental problem is that the exit hole in the shroud panel is too small.

We cannot find OMC trans unused beam at all:

We also tried to see the unused OMC trans beam that comies out into -X-Y direction, but couldn't. Maybe the power of that beam is much smaller than the video beam.

Because of this, and because they did the aforementioned Bests/TJ/Fil/RichM/Peter/Koji/Calum trick for the old OMC, and because there's no position reproducibility whatsoever once that trick is used and the panel removed and reattached, there's no guarantee that the beam will come out once the panel is installed.

If the panel weren't there, it's unimaginable that the beam will miss the V-dump. Again, the problem is that the hole is too small. That was a problem in 2016, and that is the problem now.

How can we move forward:

Could we NOT reinstall the two problem shroud panels in -X-Y and +X+Y side?