Yano, Hirata, Aso

We adjusted the beam path in the IFI chamber after the reinstallation of the IFI.

Beam centering of the STMs

The MC was unlocked and the MCe was put in the misaligned state to prevent the MC from flashing.

Then the beam spots by the single path transmitted beam were inspected.

The ideal beam spot positions on the STMs are shown in here and here.

The beam spot on the STM1 was already at the desired position.

We then steered the STM1 to put the beam at the desired position on STM2.

Sending the beam to IMMT1

We then adjusted the tilt of the STM2 to send the beam to IMMT1 through the IFI.

We first adjusted the beam spot on the IMMT1 to be centered. [image]

However, we realized that the more important point is the transmission through the viewport behind IMMT1.

We then checked the beam position at the viewport. The transmitted beam from the IMMT1 is supposed to transmit the viewport at exactly the center. However, it was slightly off to the right viewed from the outside of the chamber. Therefore, we tweaked the angle of STM2 to put the beam at the desired position. This means the beam spot on IMMT1 is slightly mis-centered at this moment. We may need to move the IMMT1 suspension a bit laterally. 

At this point the beam reflected from IMMT1 does not reach IMMT2 (hitting the suspension pillar on the right of the mirror). A large Yaw rotation of IMMT1 is necessary, which should be performed by pushing the suspension cage.

Checking the beam positions in the IFI

With this state, we checked the beam positions in the IFI. For most components, the beam is nearly centered in the aperture within, say, 1mm. However, the last CWP is slightly mis-centered, say, by 3mm. However, still the beam is well within the aperture of the CWP. Additionally, we found that the SiC aperture before the last CWP is a bit too high. We should lower this aperture.

While the beam centering is not perfect, we think it is within the acceptable range.

Ghost beams

We briefly checked the ghost beams around the IFI and found it was a mess. We will investigate this further tomorrow.