Block diagram detailed description - page 1

Basically,we use three different devices for the current measurement:a "Parametric Current Transformer",also called " UNSER" (the name of his inventor),and two resonnant cavities,usually called BCMs". The two cavities are placed around the Unser on the beam line,one Upstream and the other Downstream;the Downstream bcm is the closest to the target. The Unser" is an absolute monitor because it measures directly the actual intensity of the beam current. Very accurate at high current, it cannot however be used during normal operations because of its unstable offset. On the other hand the cavities, which are relative monitors, are stable and linear over the entire dynamic range. Therefore the basic principle is to calibrate the BCMs with the Unser monitor at high current, and then use them during the experiment. These three devices are very sensitive to temperature variations; in order to prevent them and get the desired accuracy, they are enclosed together in a big grey thermostabilized box. This is the first object on the beam line inside Hall A. The temperature inside the box is controlled from the counting house via five thermocouples located on: the Unser the Upstream BCM the Downstream BCM the copper shield the inside of the walls.

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