Sheila, Jeff, Evan
We had repeated locklosses handing off the DARM sensor from ALS DIFF to AS45Q. We changed the guardian so that the handoff happens at a slightly lower CARM offset, and with a different DARM loop gain (we had previously used these settings back in late February). This new CARM offset makes the AS port more unstable during the DARM handoff, but it makes the transition successful.
We were able to make it to resonance on rf darm, but with a mediocre recycling gain (30 W/W). We spent some time manually steering the ITMs in order to bring the recyling gain up to more than 40 W/W. Then we updated the TMS QPD spot positions and the green alignment references (green QPD offsets and camera positions). It is not clear to us why we had to do this, since we restored all the suspension alignments from before the maintenance work.
We did an initial alignment starting with the new green references. Subsequently, we came into resonance with good recycling gain (>40 W/W) again.
We were able to engage the ASC with these new spot positions. However, at 17 W we saw the same 0.4 Hz resonance that we saw a few days ago, meaning we should not power up further in this configuration.
We redid the dark offsets for the TMS QPDs, since they seemed to be stale.
For now, the DARM handoff has been returned to its old CARM offset. I have left the DARM gain slightly lower than before (80 rather than 125).
The ITM QPD offsets have been reverted to yesterday's values. We are able to engage them as usual in the ENGAGE_ASC state, and they give a good recycling gain. However, at 23 W the interferometer unlocks suddenly after a few minutes. The transmitted arm powers seem slightly less stable than with the new offsets tried above (a slow oscillation with a few-second period can be seen in the arm powers, as well as POP LF), but there is no 0.4 Hz oscillation.