[Komori, Ushiba]

Abstract:

We aligned the IMMT1 and PR2 angle with respect to the OpLev values when the best sensitivity was achieved (2025/4/29 21:30 UTC).
Then, we tweaked INP2 and PRC2 offsets and found that the current offset value seems still working well in terms of the peak height at 116 Hz.
Also, we found that BPC seems slowly drifting and degrade the alignment, which causes the lockloss, so BPC should be retuning not only for better sensitivity but also for the stability improvement.

Detail:

Since IMMT1 and PR2 OpLev value was far from those when the best sensitivity was achieved, we aligned these mirrors with respect to the old OpLev values.
Figure 1 shows the time-series data during the alignment.
There seems no significant effect on PRG and arm alignment.

Then, we once turned off INP2 and PRC2 ASC offsets to see what happens.
Figure 2 shows the comparison of the DARM spectrum when offsets were zeros (blue) and offsets were nominal values.
The peak at 116 Hz seems reduced, so the nominal offsets value seems better than at least zeros.

During the work, we found PRM is drifting in +yaw direction with several tens of minutes after reaching OBSERVATION state (fig3).
This drift seems degrades the IFO alignment and causes the lockloss, so the longest lock during commissioning today is about 30 minutes.
So, this issue should be fixed.