As it was noticed from the IMC TF plot attached to the original entry, we suffered a substantial decrease of UGF in the transfer function of the IMC. This morning, taking advantage of a break during the ISC activities, we went to the piscina to investigate a bit and found out that it was possible to restore the UGF to reasonable value by decreasing the attenuation of the error signal fed to the rampeauto by 6dB (from 6dB to 0dB).

The UGF was below 50KHz before the intervention, it is now at around 120KHz (see attached plot: purple before intervention, blue after intervention).

This is most likely due to the fact that we did not compensate the power on IMC_REFL when we decreased the power sent to the ITF. This must be done by acting on the IPC8 via the axis 2 channel 1 in the Electronic Injection Room. The target power measured by IMC REFL when the IMC is locked should be of around 0.25V (as it was during O3b), currently it is around 0.14V. We will do it as soon as a window of opportunity opens up.