OPERATION OF THE OPPOSITE-FIELD SEPTUM MAGNET FOR THE J-PARC MAIN-RING INJECTION

An opposite-field septum magnet system has been developed for J-PARC main-ring injection. The features of the system are a force-free structure and easy pulse excitation, as well as the possibility of a large-aperture and thin-septum structure (1). In the case of JPARC main ring injection, a larger beam aperture than the full acceptance of the ring can be obtained at the injection septum magnet for low-loss injection. In this paper we introduce an outline of the opposite-field septum magnet system and methods to eliminate error fields caused by fabrication errors and eddy currents by pulse excitation. The stability of a high current pulse power supply of 48 kA is also discussed. simultaneous excitation. The beam-separation angle per septum length is twice as large as that of the normal septum magnet with the same magnetic field. The two sub-bending magnets also enhance the injection angle, like a mass-less septum, and also have a role to produce a bump orbit to close the circulating orbit to the septum during the injection/extraction periods. The thin septum structure makes it possible to obtain a sufficient aperture of the septum magnet which reduces the load of the kicker magnets.