Abstract: A dipole magnet structure includes a pair of spaced pole pieces and a pair of permanent magnets secured in alignment with the pole pieces and connected by a magnetically conductive yoke for producing a uniform magnetic field within a predetermined spacial volume therebetween. The opposed faces of the pole pieces are dish-shaped with a flat center area surrounded by an outwardly and forwardly curved rim surface which extends from the center area and which increases in forward curvature as it extends away from the center area to insure homogeneity in the predetermined spacial volume as defined by the space between the pole piece center areas.