A damper for NE violin modes has been prepared and used effectively. At LN2, MIR CORR and B1 Audio were still high but not saturated: the unlock could be due to something else. Anyway, I will try to damp a bit more next time at CARM NULL.
The amplitude of the violin modes has been further reduced: now at CARM NULL they stay well below the DARM line at 491 Hz (fig 1). Given that yesterday CARM NULL has been reached with the violins 100 times larger, I would conclude that now they should not prevent the lock acquisition up to CARM NULL and the current difficulty to ramp the carm offset is more likely due to bad weather.
In DC readout the situation could be more critical: the violins are the largest component at high frequency (fig 2). Looking at the time domain (fig 3), it seems that this component does not determine the saturation of the photodiode: the reason of the unlock is not clear to me. Anyway, I would like to damp the violins a bit more. Unfortunately the largest peak (447.3 Hz) does not react anymore to any action: now the only effect is to excite the other peaks. I will try something different tonight or tomorrow, if we manage to stay at CARM NULL.
