Adding a beam dump on the squeezing bench yesterday did not have an impact on it
It is unlikely that the work on SDB2 is the cause of these new bumps. But many other activities occurred in parallel.
Bruco shows that highest coherence with environmental channels is for DAQ_FMOD_56MHz_phi
Figure 4. Indeed there is a bump at 20Hz in the 56MHz modulation that wasn't there a week ago. It seems to have appeared on Feb 18 between 15:30 UTC and 17:30 UTC.
Looking at the logbook, the most related action is the work on injection system realignment on EIB
After the realignment of the beam, the IMC locking point was also readjusted (see attached plot 1).
The DAQ_FMOD_56MHZ signal is the amplitude modulation of the 56MHz after the IMC.
This working point clearly modify the coupling of IMC length noise to the 56MHz sidebands (see #42249 and plot 2) and
could explain the correlation with of the horizontal beam pointing fluctuation, the resonances of the bench and the 56MHz noise.
The coupling of the 56MHz with the mode cleaner length could be minimized by changing the IMC locking point but indicates a mistuning of the 56Mhz modulation frequency (a few Hz). with respect to the IMC FSR.
