Virgo Logbook

The horizontal position of SNEB is not centered; the central position of filter-0 is about 2.2 mm off-center to have the bench at its nominal offset. The horizontal microsprings 0 and 2 are at the end of the range and only move in the wrong direction. Since september 2025 the horizontal DC actuation force to keep the bench centered slowly increased; now it is at +1.0 V for actuators 0 and 2. We can deliver 10 V but the DMS system gives a warning based on the DC current readout for actuators 0 and 2 (SBE_SNEB_ACT_F0H0_raw and FOH2_raw) at 4V (the current gain is amplified; the actual voltage over the coil is 1 V). We can only restore this by rebalancing the suspension by opening up the minitower so it is an action that we would do after the end of the run.
For that reason, I asked the operator (Francesco today) to change the warning in the DMS for SBE_SNEB_ACT_F0H0_raw and F0H2_raw) to +/- 8 instead of +/- 4. This will not impact the operation of the suspension noticably; we are only at 10% of the maximal DC power and the mechanics filters the (minimal) DAC noise we inject; the noise from the continuous DC current is much less than the fluctuations in actuation current needed to damp the microseismic movements.

The end position of the microsprings was reached in june 2025 (as far as I recall); since then the horizontal position slowly moved. The DMS plots for actuator 2 current are included for june, october and november.