[Takahashi, Matteo, Eleonora, Yuhang, Enomoto]

With the help of Takahashi-san, we have opened the vacuum chamber in the end room (only the top part).

[Note that even if the venting was started last Friday the vacuum level was still not low enough so we had to inject some air before opening the chamber.]

The goal was to recover the alignment of the end mirror and solve the issue with the yaw picomotor reported in the entry #954.

By visual ispection, we could confirmed that the picomotor was stuck, as it reached the end of its range, and the intermediate mass was touching the damping magnets.

We have manually put back the yaw picomotor at half range and moved the suspension with the help of a traslation stage (pic1) and also by hand, to make the reflected beam superpose on the incoiming one. The superposition was checked by letting the incoming beam pass through the hole of the second target and check the reflection from the end mirror on the rear side of the second target.

The chamber has been closed and the punping down has been restarted. The gate valve between the chamber and the pipe is still close. According to Takahashi-san, the vacuum level to be reached before opening it is 2e-7 Torr.

Even if the alignment has been recovered we were not able to see any flashes, probably beacuse the beam distortion induced by the gate valve window is too large.

Some comments:

1) The good direction for recovering the alignment was not the one in which the picomotors reach the end of the range, meaning that the suspension position and the overall alignment hadn't moved too much. In any case we prefered to move the picomotor to exactly mid range (and have an optimally centerd intermediate mass), and then move the whole suspension to recover the alignement

2) We confirm that the yaw picomotor is quite critical as by moving it it's easy to make the intermidiate mass touch the magnets. For this reason also in KAGRA during the in-air alignment procedure, the whole suspension is usually moved with the help of some pusher (see Fig. 2)

3) We checked that the beam was well centered on the end mirror and slightly adjusted the camera in the end bench in order to have the beam also centered on it.

4) Some pictures of the current position of picomotors and intemidiate mass are shown in Figs 3, 4, 5.