After the maintenance we set the ITF in LN2 and allowed about 10 minutes for the state to stabilize, before proceeding with the exploration of the stability range of SRCL_SET.

We closed BS_TX in full bandwidth and opened the SRCL_SET servo, then started changing SRCL_SET in steps of 10, one minute per ramp, allowing 20 minutes for each new state to stabilize and gather data. We managed to make a three points scan:

the ITF unlocked a few minutes after the last change of SRCL_SET (Fig.1).

We relocked the interferometer and decided to explore the margin of the scan more granularly. After reaching LN2 we set BS_TX in fbw and disabled the SRCL_SET servo again, then we set SRCL_SET to -20 with a two minutes ramp, allowed about 15 minutes to stabilize. We started changing the SRCL_SET in steps of 2, with one minutes long ramps, but realized after the first step that very little changes with such a small step while the duration of the test becomes considerable. For the next steps, we changed SRCL_SET in by 4, with two minutes long ramps.

The ITF unlocked about 10 minutes after step 4 (Fig.2)

The sensitivity was unexpectdly high for LN2, but the correct reconstruction of Hrec needs to be checked.