Ion beam bending magnet for a ribbon-shaped ion beam

An ion beam bending magnet provides a curved path through the magnet for bending a ribbon-shaped ion beam having its major cross-sectional dimension normal to the bending plane of the magnet. The magnet comprises a ferromagnetic yoke surrounding the beam path and having an internal profile in cross-section formed of four angled sides. These sides are angled to the major dimension of the ribbon beam passing through the magnet, so that the internal profile of the yoke is relatively wide in the center of the ribbon beam and relatively narrow near the top and bottom edges of the ribbon beam. Electrical conductors against the internal surfaces of the yoke provide a uniform distribution of electrical current per unit length along the angled sides of the profile, providing a substantially uniform magnetic bending field within the magnet yoke.