After completing the realignment activities and confirming that we could lock the ITF until LN2, we went in piscina to install the necessary hardware for the RAM noise injection. We set it up for 6 MHz and corrected the phase shift on the LNFS as explained in entry 62346.
Between 12:30 and 15:30 UTC, we attempted to relock the ITF. Initially, there were telecommunication issues with the LNFS server and Metatron. The ITF unlocked twice—first at 3f and then at 1f—before eventually locking at LN2 around 15:30 UTC.
The DAC dedicated to the RAM noise injection was used to do the noise injection. We injected noise in two phases: first, a line at 111.1 Hz, followed by colored noise both in LN2 and in LN3. There is a 9 V offset on the DAC to ensure proper operation of the input mixer of the electronis for noise injection However, since the DAC is limited to 10 V, we were unable to observe any noticeable effects on the ITF signals for the line injection when the amplitude was less than 1 V or for colored noise that did not exceed 10 V.
Instead when we exceeded the DAC’s 10 V limit, it began to saturate, and as a result, we were injecting not only the 111.1 Hz line but also its harmonics, due to signal distortion. In this scenario, we were able to observe clear effects on the ITF signals. I’ve attached plots of these effects. The times of the most relevant injection are at the bottom of the entry. Additionally, I am attaching the log file from VPM with the GPS time and noise amplitude data.
At this point, it's difficult to draw any conclusions. We will better analyze the data to see if there is something to understand, maybe upper limits by using the INJ_EOM_6MHz_mag signals.
We would need to repeat these measurements. One potential solution could be to use a dedicated waveform/noise generator at the input of the injection electronics and acquire the data on an ADC for reference.
#### LN2 ####
15:48:40 line 111Hz ampl 3 dur 1 min
16:50:20 ampl 2.8 dur 2 min
16:52:40 ampl 2.5
#### LN3 ####
17h11 linea 111Hz LN3 5 min
18:17:10 bandpass 111-333 Hz 1e-2 2 min
18:19 bandpass 8e-3 2 min
18:21 bandpass 6e-3
