Evaluation of beam loss at a branching point of the J-PARC Hadron High-p beamline

The J-PARC High-momentum beam line (High-p line) is under construction at the J-PARC Hadron Experimental Facility. Primary proton beam at 30 GeV is branched to the High-p line by a Lambertson magnet in which a fairly large beam loss is inevitable because an edge of the magnet pole is exposed to the primary beam to separate a portion of the beam. In the beam time in 2019, several types of beam-loss monitors were equipped around the Lambertson magnet. By using the monitors, a beam-position dependence of the beam loss was measured. As a result, the beam loss is estimated to be 25 W in the extraction mode to the High-p line. The amount of the loss is found to be a reasonable level, and thus requirements for radiation safety are satisfied. (author)