Nakano, Hirose, K. Tanaka

## Summary

In the previous survey, it was a little unclear whether the beam was hitting the center of the PRM so we checked where is the IR beam spot on PRM again. As a result, the beam spot on PRM is shifted 7 ~ 8 mm from the center of PRM. Consider that the beam spot at PR2 is at the center of PR2, the current optical axis is tilted from the ideal optical axis that passes through the center of PRM and the center of PR2. However, even taking this into account, the position of the beam spot on the IMMT2 is off from the center of the IMMT2, so It may be necessary to relocate IMMT2 in - Y direction.

## What we did

First we opened the flange on the +Y side of the PRM chamber and attached the beam target in front of the PRM AR side. Then we checked the position of the beam spot on the AR surface of PRM by holding a sensor card with a ruler(Fig 1 and Fig 2). From the ruler, it was confirmed that the position of the beam was shifted 7~8 mm from the center of the PRM to the -Y side.

In the previous survey, the beam spot position at PR2 was found to be at the center of PR2. This result indicates that the current optical axis is tilted from the ideal optical axis passing through the centers of PR2 and PRM. The estimated position of the beam spot on IMMT2 from the current optical axis is about 9 to 10 mm off the center of IMMT2 to the -Y side.

According to Yano-san's photo analysis(Fig 3), the actual position of the beam spot at IMMT2 is about 17 mm. It is larger than the estimation. Therefore, if the beam spot is at the center of PR2, the center of IMMT2 should be off by about 7 ~ 8 mm from the ideal optical axis to the +Y side.

Anyway, first we should make sure that the beam is hitting the center of PR2, and worst case, we may have to move IMMT2 to the -Y direction.