A study of the prism-ffag magnet

PRISM is a facility to provide a high intensity, high purity, and high brightness muon beam based on a novel technique of phase rotation, which is usually used in a synchrotron [1, 2, 3]. PRISM consists of 1) a pion capture section, 2) a pion decay and muon transport section, and 3) a phase rotation section. In the pion-capture section, pions produced backward from a target are collected with a surrounding solenoid magnet of about 10 Tesla. Pions decay to muons in the succeeding decay region, and the muons are transported to the phase rotation section, where the phase space of the muons are phase-rotated by a synchrotron oscillation. In PRISM, a Fixed-Field Alternating Gradient (FFAG) synchrotron is used as a phase rotator. PRISM aims at high intensity of 10-10 muons / sec and the energy spread of less than 2 % at central energy of 20 MeV/c. To achieve such high intensity, PRISM has a high gradient RF system [4]. and the FFAG magnets which have a large acceptance. From the PRISM-FFAG ring, the required acceptance is more than 20,000 π mm mrad in the horizontal phase space and 3,000 π mm mrad in the vertical one. To achieve this acceptance, the PRISM-FFAG magnet needs to have wide geometrical aperture more than 100 cm in horizontal and 30 cm in vertical. The magnets have been designed by using a 3D magnetic field calculation program.