Today we continued the recovery of the ITF. We managed to reach LOW_NOISE 2.

At the beginning we noticed a lower power values on the 112 and 12 MHz sidebands, which was taken care of by Ilaria, acting on CH:

NI CH = 0.577W -> 0.708 W

WI CH = 0.324 W -> 0.416 W

At the end, we partially reversed the NI CH PWR increase: 0.708 W -> 0.630 W. (17.32 UTC finish of the actions).

After this, we had several issues in finding a good configuration of demodulation phases in order to get past the handoff from 3f to 1f in CARM null. In particular DIFFp was showing during the transient some misbehaviour (not entirely clear the rigth explanation), in which with good phases both I and Q (on TX DoF) were witnesses of some movement which ended up in a quick drift of the alignment and eventually the unlock. Curiously enough, the phase able to get past the initial transient was showing a ~45 deg mistuning. After several trials in which we noticed this behaviour, we implemented a double condition in the automation in which we use two phases, one 'wrong' for the transient and one good for the steady state (similarly to what we do for B4 56 MHz).

With this configuration we were able to lock the OMC, after a tuning of the OMC locking phases, and go up to LOWNOISE 2. However, after a while we unlocked due a to a WI tower pump failure. Antonio went to CEB  to take care of it.

We leave the ITF locking on LOWNOISE2 for the night, to acquire some statistics on the acquisition.

N.B. the modification on the automation are the following:

ITF_LOCK.py: added lines 4681-82; 4685-86.

ITF_LOCK.ini, in the SHUTTER section: added the steady state DIFFp phases.

If the acquisition is robust enough, tomorrow we will proceed to fine tune all the several phases, if needed.

:)