The magnetic field calculation and the electron trajectory determination in computer aided design of unsaturated magnetic lenses

The present paper is devoted to the calculation of the magnetic field and to the determination of electron trajectories for some magnetic lenses of particular interest. In the pole-piece region the field is determined by means of a scalar potential, while in a complete magnetic circuit by a vector potential. For both cases, finite element based methods of computation are presented as well as adequate programming techniques. (Author)