Production and optical properties of an unscreened but localized magnetic field

Abstract

A technique is described of using current carrying coils to produce a magnetic field that is well localized, falling off quickly with distance. The basis of the technique is that the first four magnetic multipole moments of the system are arranged to be zero. The deflection and electron optical properties of this type of field are then investigated. It is shown that a beam that initially converges to a point on the axis of symmetry of the field will be deflected in such a way that it still passes through the axis. Similarly, a beam originating at the axis will be asymptotically radial but with a changed direction.