Bulk reduction and field enhancement in periodic permanent-magnet structures

Permanent.magnet structures are described in which the longitudinally oriented flux-supplying magnets of a conventional periodic configuration are clad with radially oriented toroidal magnets shaped to confine the flux to the working space of the stack bore. Such cladding increases the useful magnetic field in the working space and eliminates potentially deleterious stray fields outside of the structure. Alternatively, cladding can be used to reduce the mass and bulk of the magnet stack without a reduction in field strength. More conventional methods of field enhancement are compared to cladding, with regard to maximum fields and minimum bulks attainable. Cladding, in combination with some of the other methods, can result in order-of-magnitude bulk reduction at constant field.