Abstract: The first order finite element method allows an accurate computation of rotationally symmetric magnetic electron lenses with saturated materials. The paper gives an overview of six methods for the evaluation of the coefficients of FEM equations. Then we present a study of local and global errors in the axial flux density distribution. These effects are illustrated on computations of a simple magnetic lens, closed magnetic circuit, and an objective lens for 1 MeV microscope. Finally we give a recommendation on the use of meshes with sufficient number of mesh points and with graded mesh size, and provide information on the computation time and memory requirements on a personal computer.!23
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