The following report has been submitted to the On-call interface.

On-call events -> Interferometer Sensing & Control

Title: Unlocks during lock acquisition

Author(s): casanueva

Details:

This afternoon the operator called me because the ITF was not locking, losing lock at different steps of the lock acquisition between STEP 1 and CARM NULL. I have taken a look to those unlocks, but I haven't understood the reason. Figures 1, 2 and 3 show examples of these unlocks. What I can say is that all the unlocks of the afternoon are like these two.
There is no real oscillation on the longitudinal loops, however at some point the sidebands on B4 (12 and 112MHz) decrease very fast (not B4 DC or B7 DC). It doesn't look like the PR angular loop follows (no change in the corrections, only the error signal that goes slightly away from 0) and just after a loud glitch happens to PR MAR TX and TY. It looks very similar to other unlocks that we have had in the past due to some short loss of data of the PR ( https://logbook.virgo-gw.eu/virgo/?r=61055), however, I did not find any evident loss of data in the channels of the PR (MIR Z CORR, F7 Y). So I am not sure why these unlocks happen.
The ITF relockes without my intervention.

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