Virgo Logbook

Today we continued the work for the recovery of the DRMI:

in order to tune the B2_6MHz_phi0 and B2_56MHz_phi0 demodulation phases we used the PRMI configuration; we needed minimal changes on the 6MHz (final value 1.26) and a quite large change on the 56MHz one; once we managed to lock, clean data is 300 s starting from 16:13:10 UTC;
in order to fine tune the 56MHz demodulation phase, we injected noise on PRCL and tried to minimize its coupling to MICH (Figure 1); the results and GPSs are reported in Figure 2 (all measurements lasted 120 s), the optimal demodulation phase was found to be 0.7;
then we moved back to the DRMI configuration, which could not be locked immediately; we found the correct gains and then we managed to lock the DRMI at 18:04:13 UTC, although the first locks lasted only for short periods;
once the locks were more stable we moved to the PR alignment loops; the standard demodulation phase seemed good enough and we could close the loops both in Drift Control and, starting from 18:10:35 UTC, also in full bandwidth; in this condition we could improve the tuning of the demodulation phases for the QPD signals (both _V and _H changed by -0.2);
during the shift the 11.5 Hz noise did not show up in a macroscopic way;
at this point the DRMI lock was very stable and repeatable for the rest of the shift, using the Automation to relock it without changes;
we moved to some characterization of the DRMI loops, using the UGF monitor lines (Figure 3); we turned them on:
- MICH @ 31.1 Hz, ampl = 2e-3, at 18:18:00 UTC, UGF ~ 21 Hz;
- PRCL @ 67.1 Hz, ampl = 1e-4, at 18:19:30 UTC, UGF ~ 52 Hz;
- SRCL @ 33.3 Hz, ampl = 5e-2, at 18:30:30 UTC, UGF ~ 2.5 Hz;
- as for the past trials, the SRCL one needed to be unusually high in order to allow a good measurement;
then we tried to recover also the lock with the 3f signals; we used the same technique as of #51156; Figures 4 to 6 show the measurements, done using the same UGF lines as before, but with much higher amplitudes in order to see something on the 3f signals; quite strangely, the ratios between 3f and 1f signals resulted to be strongly different with respect to the past;
we tried the handoff three times, but all of these were unsuccessfull and resulted in an unlock; Figure 7 shows the last trial, the GPSs are: 20:06:28 UTC, 20:21:04 UTC and 20:30:08 UTC; between one trial and the following one the DRMI relocked automatically without issue, although after the first two unlocks the PR parked itself;
we investigated a bit this issue, and we found out that there could be some issue on B2_PD1, which shows signs of possible saturation (Figure 8); the investigation on the 3f signals will continue;
all the updated parameters have been stored in the configuration file of the DRMI_LOCK automation node.

At the end of the shift we parked PR and SR and relocked the arm cavities on the IR beam.