Hirata, Akutsu; following 29723.

Summary

We found that the main light beam location at the aperture of PR2 HR mid baffle was almost centered when centering the beam spot on PR2 (to precisely put, PR2 HR target). This means PR2 HR mid baffle is dislocated with respect to the main (forward) beam, unfortunately. My conlusion is that this baffle needs to move about 5 mm in the minus Y direction next week.

Details

As discussed in the morning, we were worried if the current light beam was not be clipped at the aperture of PR2 HR mid baffle. So we started with checking the aperture edge with the Miyakawa-san's IR camera, and no shining in IR found. However, at the same time, we found that the beam passed through the very center (or even shifted in the minus Y direction slightly) of the aperture (Fig. 1).

Nominally, the input beam to PR2 should pass through 6.3 mm shifted in the plus Y direction with respect to the center the aperture of PR2 HR mid baffle (JGW-T1910200-v4). Otherwise the light beam reflected at PR2 toward PR3 would be clipped at this aperture. Because we have not yet determined the "nice" alignment of PR2, we could not make this light beam so far, unfortunately. So we could not check if this reflected beam would be clipped here or not. At any rate, if the input beam would be centered, or in other words, off-centered about 6.3 mm in the minus Y direction with respect to PR2 HR mid baffle, this document says that the reflected beam would be clipped, as the 2.8-sigma edge of this reflected beam is only 4.6mm away from the aperture edge.

So, we need to move PR2 HR mid baffle 6.3 mm (or let's say ~ 5mm) in the minus Y direction.

The drawback of this move is: the invac POP-POM is on the same suspended breadboard as that for PR2 HR mid baffle. When this baffle moves, the balance of the breadboard might be affected, and the alignment of invac POP-POM may also vary slightly. The invac POP-POM is steering (1) POP_FORWARD and (2) GRX to PR3, so both of them should be affected. In short, we have to repeat Day 1 work for GRX, and Day 2 work for POP_FORWARD later. Our hope is that the suspended breadboard does not have vertical springs, so the balance variation might be very small, altough this means no vertical vibration isolation for the stuffs on this breadboard.

Anyway, moving PR2 HR mid baffle will be done in the next week. Hirata-san found several tools used in the past to move this. For reference, see 19291.

Note

• By the way, it would be kind of of-course, no shining maybe due to clipping was found at the aperture edge of PR2 HR mid baffle with the Miyakawa-san's IR camera.
• During this work, we were disturbed by a strange ghost beam, and finally found that this was due to a window attached to a gate valve between PRM and PR3; this GV had been closed. So we opened it.