Matteo, Takahashi-san, Yuhang

Takahashi-san removed the jig and released BS earthquake stop this morning. Before closing vacuum chamber, we checked transfer function of BS and pitch/yaw coupling.

The transfer funtion shows in the first attached figure. We can see that the red line is close to reference below about 10 Hz. The deviation at low frequency is probably due to the air flow, while the deviation at high frequency is presumably due to acoustic coupling.

The pit/yaw coupling shows in the second attached figure. The green shows the coupling when we have magnet drop. The red curve is after we put new BS magnet, which got close to reference (blue curve). This figure shows that the BS mirror magnet replacement work is successful.

After confirming TF and coupling, we closed both PR and BS chamber and evacuated them. Now, we are using turbo pump to evacuate. Until the vacuum level reaches about 1e-8 mbar, we will open the gate valve between PR/BS and Input.