[Anchal, Paco]

We opened BSC and Injection Chamber doors. We removed two stacked counterweights from near the center of the BS table, from behind TT2 and placed them in the Xend flow bench. Then we unscrewed TT2 and relocated it to the new BHR layout position. This provided us with the target for the alignment of MMT1 and MMT2 mirrors.

While aligning MMT1 and MMT2, we realized that the BHR layout underestimated the clearance of the beam from MMT2 to TT2, from the TT1 suspension unit. The TT1 suspension stage was clipping our beam going to TT2. To rectify this, we decided to move the MMT2 mirror mount about a cm South and retry. We were able to align the beam to the TT2 optic, but it is a bit off-center. The reflection of TT2 now is going in the general direction of the ITMX chamber. We stopped our work here as fatigue was setting in. Following are some thoughts and future directions:

• We realized that the output beam from the mode cleaner moves a lot (by more than a cm at MMT2) between different locks. Maybe that's just because of our presence. But we wonder how much clearance all beams must have from MC3 to TT2.
• Currently, we think the Faraday Isolator might be less than 2 cm away from the beam between MMT1 and MMT2 and the TT1 suspension is less than 2 cm away from MMT2 and TT2.
• Maybe we can fix these by simply changing the alignment on TT1 which was fixed for our purposes.
• We definitely need to discuss the robustness of our path a bit more before we proceed to the next part of the upgrade.

Thu Oct 28 17:00:52 2021 After Photos: https://photos.app.goo.gl/wNL4dxPyEgYTKQFG9