R&D (FilterCavity)
YuhangZhao - 15:57, Monday 18 October 2021 (2712)
Filter cavity BS mirror is found to have some problems

After the earthquake on 7th this month, we confirmed the normal operation of vacuum system, mirror suspension system. Especially, the filter cavity alignment was recovered and mirror's oplev shows usual spectra.

However, we found already that the driving of BS has problem. The problem is when we try to move yaw or pitch, the beam reflected by BS moves diagonally.

To confirm if there is any issue for magnets, I took a photo of BS magnets. Attached photo shows this check. Two red boxes indicate the location of four coil-magnet actuators. An arrow points to the magnet which seems to be broken. This magnet may be knocked during earthquake and get tilted. So the coil cannot drive it properly.

Images attached to this report
2712_20211018085711_57.png
Comments related to this report
YuhangZhao - 11:54, Wednesday 20 October 2021 (2719)

We have done some more check before opening the BS vacuum chamber.

1. Check BS P and Y transfer functions. They are similar with reference as shows in the fig1 and fig2.

2. Check coupling between P and Y. A substantial coupling increase is found as shows in the fig3.

3. We tried to close BS local control loop. But failed.

The results of test 2 and 3 make us really need to open BS chamber to check. The opening work is scheduled to be in this afternoon.

YuhangZhao - 16:29, Wednesday 20 October 2021 (2720)

Marc, Matteo, Takahashi-san, Yuhang

We opened BS chamber today to check if there is any issue for the magnet.

We found one magnet falls down as shows in the attached figure.

Takahashi-san will help us prepare a replacement magnet. The replacement work will be done in the next next week.

RyutaroTakahashi - 17:06, Thursday 21 October 2021 (2722)

We started evacuation of the BS chamber yesterday. I opened the gate valve between BS and NM2 today.