A fast profile monitor with scintillating fiber hodoscopes for high-intensity photon beams

A fast beam-profile monitor has been developed for high-energy photon beamlines at the Research Center for Electron Photon Science, Tohoku University. The position of the photon converted into an electron–positron pair in a 0.5mm-thick aluminum plate is measured with two hodoscopes made of scintillating fibers with cross-sections of 3×3mm2. Events in which charged particles are produced upstream are rejected with a charge veto plastic scintillator placed in front of the plate, and pair-production events are identified with a trigger plastic scintillator placed behind the plate. The position is determined by a developed logic module with a field-programmable gate array. The dead time for processing an event is 35ns, and a high data acquisition efficiency (~100%) can be achieved with this monitor for high-intensity photon beams corresponding to 20MHz tagging signals.