ETMX OpLev SUM is now about 100 cnts while it was ~10000 cnts before cooling, so I started to investigation.
Figure 1 shows the MN OpLev SUM when changing the MN Optic align values at PAY_FLOAT state.
When MN Optic align values are -1200 cnts from the aligned position, MN OpLev SUM is more than 9000, which implies that MN OpLev beam is clipped somewhere.
Since the cooling would change the relative angle between TM and MN, this phenomena can happen even if we kept the good alignment of ETMX.
What we can do depends on the situation:
1. If the clipping happens on the BS of the detection port, we can recover it by realigning the optics on the reciever side.
2. If the clipping happens inside the cryostat, we need to move injection beam to recover the clipping.
Anyway, ETMX MN OpLev damping performance getting worse and it is dificult to lock the interferometer stably in this condition, so we need to fix the probem.
