This afternoon the B7 and B8 beams have been precentered on the SNEB/SWEB quadrants while the ITF was locked in recombined. The corresponding signals when after this precentering are shown in Fig.1 and Fig.2.

The following steps were performed on the picomotors:

B7 Mmot1 V +15800 ; B7 Mmot1 H +2150

B7 Mmot2 V +11100 ; B7 Mmot2 H -1000

B8 Mmot1 V +17600 ; B8 Mmot1 H +1000

B8 Mmot2 V +5600 ; B8 Mmot2 H +700

Then the ITF was locked to the dark fringe. The corresponding signals on the quadrants are shown in Fig.3. On SNEB the B7 quadrants asymmetry channels remains around 1V, indicating that the centering can still be slightly improved, and showing that the alignment fluctuations are sufficiently small to be monitored with these quadrants.

On the other hand on SWEB, the B8 quadrants asymmetry signals have large fluctuations (from 0 to 10V), which will make it difficult to avoid the ADC saturation.

We will need to check on longer time scale at dark fringe whether the beam centering on these quadrants can be further improved.

It must be highlighted that while this activity was being performed, a drift of the B8 beam position of the camera and on the photodiode was observed. This drift was recovered by changing the setpoint of the SWEB bench in TX from 90 to 115 urad. At this time, it is not understood what caused such a drift. We thought about a possible thermal effect due to the switching on of the SWEB picomotor drivers, but the beam drift seems to have started a few minutes before the use of the drivers. To be further investigated.