A double-gap planar magnetic lens

An analytical model and equations for describing the field of a planar magnetic lens with two concentric nonmagnetic gaps are developed. It is demonstrated that the “half-width” of the magnetic field of the lens can be controlled by varying independently the currents in the excitation coils of the two gaps. This makes it possible to control the focal length and the spherical aberration of the lens. It is shown that when oppositely directed currents are used in the excitation coils, a planar magnetic lens that does not rotate the image can be obtained. Zh. Tekh. Fiz. 69, 133–134 (August 1999)