Clad periodic permanent magnet structures for electron-beam guidance

Permanent magnet structures are described in which the longitudinally oriented flux supply magnets of a conventional periodic structure 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. Similar cladding techniques can be used for constant field sources, as well as for other periodic structures such as wigglers. These are compared with their conventional counterparts with regard to field-produced per unit structural mass.