Development of a high-intensity photon-beam profile monitor

Several beam-profile monitors have been developed for high-energy photon beamlines at the Research Center for Electron Photon Science, Tohoku University, Japan. The position of the photon converted into an electron-positron pair in a metal plate is measured in these monitors. In the current monitor, two layers of 16 scintillating-fiber hodoscopes with a cross section of a 3-mm square have been adopted for the position measurement. The effective area is a 48 mm square. 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 logic circuit with a field-programmable gate array. The dead time for processing an event is several tens of ns, and a high data acquisition efficiency can be achieved with these monitors for high-intensity photon beams (approximately 400 MHz). In the new developing monitor, the scintillating-fiber hodoscopes are planned to be replaced with a multi-anode metal-packaged photomultiplier tube. The secondary emission electrons produced at the photoelectric surface by the electron-positron pair are utilized for the position measurement. In this contribution, the overview of the developed monitor and prospects of the developing monitor will be discussed.