Today we tried to recovery a stable lock in CARM null 1f in order to proceed with the TCS tuning, however we encountered some troubles during the shift.

We weren't able to find a stable lock up to carm null , unlocking most of the times at CARM step 3/3 (or randomly before), so right before carm null 3F.

At first we didn't find any clear explanation to the several unlocks. We tried to tune the sevaral phases and gains in order to make more robusts the steps, with no success, without even being able to engage the Diffp loop in drift control. At the end we found a correlation to a misfunctioning of the NI Etalon loop.

After the adjustement of the setpoint performed in the beginning of the afternoon (https://logbook.virgo-gw.eu/virgo/?r=69752) we noticed that the loop was still not properly working since it was not converging correctly to the setpoint as the temperature was still increasing above it, see fig.1.

A correlation was found with the Etalon misbehaviour and a change in the sidebands powers alonf the shift, see fig.2.

Expert was notified about the issue. Investigation will be performed to understand if the misfunctioning is at the level of the hardware or at the level of the control loop logic.