Computer-aided design of saturated round magnetics lenses

The problem of lens convergence because of very high voltages used in electron microscopy can be mastered with superconducting lenses, the magnetic circuit of which is partly saturated. The equations of magnetostatics have to be solved directly for the investigation of the properties of such lenses. A network method is used and it is shown how to establish finite-difference equations for the solution of equations referring to saturated magnetic materials. A computing program for symmetrical lenses is described, and the accuracy of the solution is estimated by comparison of the computational results with those measured on an actual lens.