A degradation of the lock has been observed in the last days. the power in the arms, locked on the IR, are fluctuating a lot. The corrections of the controls are saturated.

analysing the trends a matching can be found with the worsening of the RFC lock due to the change of filter (1/f instead of 1/f4).

Figure 1 shows the trends from datadisplay in which is visible that the spoiling of the cavity is more or less compatible with the worsening of the rfc accuracy

Figure 2 shows the matlab analysis:

in this analysis only the locked periods (for both arms are taken) averaging on 100sec. The first two plots shows the maximum power and the variation of the power for the two cavities. A worsening is visible in the recent days. The third plot shows the accuracy of the RFC lock, worsened after the change of filter and the last one shows the Sc_NI/WI_MIR_Z_CORR variations and it is visible that they starts to saturate when the RFC filter is changed.

this situation is visible also in Figure 3 when the two RFC control spectra are compared, showing also the cavity signals.

The control should turned back to the 1/f4 control.