Miyo, Fabian, Hirata, Ushiba, Akutsu Cont'd from 17170.

Abstract

The green beam reached the IXA chamber. Before going further more, off-loading in the PR3 components was required (see 17187).

Before and after PR3

Just looking at the green beam spot (masked by the slit pattern on the PR2 target plate) on PR3, I assumed steering mirrors somewhere drifted in this weekend, or suspected that the picomotor-driver disconnection (I did it for safety in the last Friday, see 17170) might shock electrically the POP-POM picomotors to cause the "mis-alignment". But it seems this is not the case. Actually, I had forgot to look at the spot on PR3 when PR2 was masked on the last Friday. The "displace" of the masked spot would be due to "parallax" of the beam with respect to the slit pattern on the PR2 target, maybe. To confirm this, we somehow checked what would happen when the picomotor driver was turned on to see if the beam spot on PR2 might move or not, but that did not happen. We moved the picomotor actuators on POP-POM remotely (with MEDM) to check the alignment on the PR3 with and without the PR2 target plate, and I confirmed the repeatability of the "displaced" masked pattern (w/ the PR2 target plate) and the "centered" unmasked beam profile (w/o the PR2 target plate). See Fig. 1. So I let this as is today. Let's see.

Confirming the beam spot would illuminate the PR3 center, I looked for the reflected beam from PR3. I surveyed around the PR3 chamber and the vacuum tube between PR2 and PR3, but I could not find... and I found the beam spot on the whity cover at the BS chamber (Fig. 2; can you see the green spot in the left of PR2?); This should be it! (but be calm not to jump to the conclusion; be careful). Considering the angluar overlapping othe beam before and after PR3, the green beam would not hit to the inner wall of the vacuum tube between PR3 and PR2... hopefully.

Through BS to IXA

Firstly the green beam transmitting through BS was clipped (Figs. 3 (from -X ) and 4 (from +X)). Miyo-kun adjusted in pitch and yaw carefully (looking at some signals...), and so the beam could pass through BS. Next, looking at the viewport window on the gate valve of IXC (in-between IXC and BS), we somehow centered the beam to the viewport. Then Ushiba-kun found the beam reached IXC and IXA.

Overall

• Now we learn the rough numbers close to the proper alignment of PR3, while some actuators of PR3 components had a large number. So VIS determined to do the off-loading (see 17187).
• By the way, Fig. 5 was taken at +X of the BS chamber after the beam passed to IXA