DESIGN AND FIELD ANALYSIS OF A LARGE APERTURE QUADRUPOLE MAGNET

High energy accelerator research organization The J-PARC main ring fast extraction (FX) system provides bipolar magnetic field for both the abort beam at any energy and the FX beam at 30 GeV. With the increase of beam intensity, one great concern is the expected beam losses in the FX system region due to the restriction of the present quadrupole (QDT155) physical aperture. An upgrade study of design a new quadrupole with physical aperture 1.5 times larger is in process. The large physical aperture not only brings the problem of material saturation but also creates significant fringe fields that affect the particle motion. Since FX magnets at downstream are dense packed, magnetic field interference between the QDT155 and the septum has to be taken into consideration. This paper introduces the optimization of the quadrupole design, and how to treat the fringe field correctly for beam optics study. 1