The beam position monitor of the BEAR beamline

This article describes the photon beam position monitor installed at the BEAR beamline at Elettra, Trieste. The device, based on four Mo photoemitting plates, is installed upstream of the beamline optics. Two modes of operation are possible, including single-plate operation sintegral moded and two-plate operation sdifferential moded. The integral mode allows beam height determination in the laboratory frame of reference with an overall accuracy of about 0.1 mm, while the differential mode features a sensitivity of the order of about 1 mm. A quantitative model connecting the device output with beam height was deduced. A satisfactory agreement was found between model predictions and experimental results. The quantitative performance opens the possibility to implement a feedback procedure to stabilize or automatically numerically correct the delivered photon energy.