The goal of this shift was to recover CARM_NULL_1F.

During the afternoon the ITF slowly continued to thermalize after the TCS actuators were enabled, causing the sidebands to rise in power at a steady rate that only started forming a plateau around 16:00 UTC (Fig.1).

This forced a continuous back and forth to adjust gains and phases, following this moving target, until the thermalization process stabilized.

Towards the end of our shift we managed to reach CARM_NULL_1F but could not stabilize this state, as a 11 Hz oscillation, slowly but steadily rising, eventually breakes to lock. The main culprit seems to be SRCL gain being too high, with the oscillation being wide enough to overwhelm the UGF servos, preventing them to adjust the gains. This oscillation is witness by a vast number of longitudinal and angular loops, making diagnosis more difficult.

Overall, the demodulation phases are adequate in 3F and good enough in 1F to allow the transition, but we could not complete their fine tuning before the end of the shift.