The need for care in providing magnetic material data in saturated FEM calculations

A number of versions of Finite Element programs are in use for the calculation of electric and magnetic fields in electron lenses. In the course of time, various problem cases have been reported, usually associated with unusual features in the geometry under consideration. It has been discovered that an algorithm used by Munro for non-linear (saturated) magnetic lenses can break down for all geometries, if supplied with unsuitable B-H data.