Introduction: we need to have a good power monitor of the neoVAN in order to assess the PMC throughput and the possible intra cavity loss

the neoVAN power is monitored into the associated diagnobox (PSL_AMP signlas) and requires the AMP_QD_NF and FF quadrants to be centered to keep the beam centered on the single element PD which delivers AMP_DC signal.

Issue:

After the work on PSL and the accidental misalignement of the seeder (42148 ) the AMP_QD signals of the diagnobox were quite offseted due to the misalignement of the neoVAN beam.

we see that before the accident the DC signals of the 2 QD PD and the single elt PD gives the ~same signals (see plot 1, phase A, see plot 2 for the legend)

after the accident misalignment the 3 signals fail to give the same value (calibrated in watt), which is reasonnable since the beam is misaligned on the diagnobox: see the 4 error signals of the QD (those 4 signals are centered arbitrarilly around 30 W on the plot for display puprose). (see plot 1, phase B, see plot 2 for the legend)

Some work has been done to get the beam realigned on the quadrant of the diagnobox ( 42193 ).

The signals of the QD seems better centered (around 30 W which means close to zero, and at least as good as before the accident), but still the 3 DC signals are still different, while we were expecting to recover the situation befor the accident. (see plot 1 phase C, see plot 2 for the legend)

I was informed that the optical density has been moved and that is has lead to some power variation, but this would impact the 3 signals in the same way I guess and is of no help to explain our specific issue.