Today, after Paolo restored the control of the SDB1 bench suspension, we noticed that the bench was not at the expected position according to the bench LVDT. We also faced some difficulties in closing the angular control loops. We noticed that the bench was not free and that a vertical displacement would be linked to angular rotations in TX and TZ suggesting that the bench was touching.

We then entered the detection tower to check the LVDT wires and noticed that the Back Right Vertical coil had an unconnected wire. This happened yesterday evening between 17 and 17h30 utc according to the data of the LVDT sensors.

Thanks to Gianmatteo, the wire of the coil was repaired and we could finish the rebalancing of the bench.

After the repositioning of the bench position with the suspension (performed by Valerio) we made a tiny adjustment of the bench angular position using the motorized counter-weight: We performed -24000 steps on BENCH_TX (by steps of -2000).

With the SDB1 bench controlled in air, we then checked the position of the injected Hartmann beam inside the tower (see Figure 1) and saw that the new beam dump is quite far from this beam. During this measurement the angular control of SDB2 were also closed, however the position loops had been incidentally left open. This does not matter for the check because the X,Y;,Z positions of the bench were only a few tens of um away from the setpoints.

At 15h55 utc we asked Antonio to reopen the valve and to stop the air flow in the tower. We started to check the alignment of the bench with the single bounce beam. With the same angular positions of the bench as we had last tuesday we immediately found the B1p beam and a little adjustment of this angular position allowed us to bring the B1p beam at the same position on the camera as we last tuesday (Fig.2). SDB1 angular setpoints changed in TX from -30 to -18, and in TY from 0 to -25 urad.

For this position of the bench we measured the beam on the B1s camera (Fig.3) at the following coordinates:
Pos X : -0.05, Fit pos X -0.03
Pos Y : 0.22, Fit pos Y 0.22

We opened the OMC shutter and scanned the OMC from 16h26 to 16h39 utc. We observed the following modes:

TEM00 : 1.7 mW (at 22.587 deg) at 16h31h33 utc (see Figure 4 and 5)
Order 1: 1.4 mW (with a pattern which was mainly vertical) - see Figure 6 and 7.
Order 2: 0.6 mW (Figure 8)

We checked from the south west viewport of the SDB2 minitower the silicon beam dump which is stopping the beam reflected by the OMC shutter, with an infrared viewer, but it was not possible to see any scattered light.

After this we gave the green light to the vacuum team to close the tower.