At the beginning of the shift we started the recovery of the lock acquisition, due to the issues encountered in the previous shift (see https://logbook.virgo-gw.eu/virgo/?r=57603).
At first, we locked in DRMI 1f/3f and we checked the tuning of the LSC DoFs demodulation phases.
MICH/SRCL and PRCL, both in 1f were good;
In 3f MICH/SRCL needed just a fine-tuning from -1.9 to -2,0 rad.
We experienced several unlock during the step CARM_MC_IR, rigth before performing the handoff:
16.16.18 UTC: unlocked before CARM2MC handoff.
16.49.24 UTC unclock before CARM2MC handoff.
17.04.07 UTC unclock before CARM2MC handoff.
In agreement with Alessio and Diana and me, we decided to go back with the DAS WI power, to the values of this morning.
This action was performed around 17.17 UTC.
In the meantime, I tried one attempt of locking the ITF, performing several steps by hand in order to try to debug the possible cause of the failing handoff.
At 17.25 I reduced the CARM MC gain from 1.3 to 1.1; then I performed the CARM handoff but, from 8.94, I reduced the MC_set to 6.3 (for a test to arrive just at 20 mW instead of 40 mW of arms power).
Then we arrived slowly by hand to 8.94 (40 mW), then we fine-tuned DARM phase for the next step (step DARM_TO_IR):
from -2.8 rad it was changed to -2.5 rad.
At this point we performed the handoff of DARM, which worked fine, as the rest of the step of the acquisition up to CARM null 1f (locked at 17.33 UTC).
To be noticed that this test has been performed right after (few minutes) Diana and Alessio did the movement of DAS WI.
18.08.05 UTC: The lock was stable, only the 1.7 Hz arised, so we engaged the COMMp (only for TY) in full bandwith in order to damp it:
18.24 We reached the alignment working point (error signal at zero), so from now on Alessio started to do the tuning of the DAS NI:
18.31 UTC first step with DAS NI.
19.02 UTC second step DAS NI
20.18 UTC third step DAS NI
After these movements the effect was a clear decrease of the sidebands and a general worsenig of the other figures of merit of the lock. So we decided to reverse the movements on NI. This step was performed at 20.32 UTC.
Situation has been recovered at around 21.28 UTC
21.44 UTC unlock
After that we experienced some unlock during the handoff to CARM null 1f
22.00 UTC unlock at CARM null 3f->1f
22.11 UTC unlock at CARM null 3f->1f 90 Hz oscillation.
Given the situation, we left the ITF locked on the IR, with the aim to perform one last step on DAS WI to be rescheduled on wednesday, together with the debugging of the last step of the lock acquisition.
