Study of the electron optical systems with broken rotational symmetry

This thesis deals with computing of the magnetic lens with a perturbed pole piece due to manufacturing imperfections. Two possible ways of calculation are discussed - the perturbation theory and 3D computing. Three methods for evaluating axial multipole field functions from 3D fields are introduced. Beam spots in the image plane and aberration coefficients are computed and results obtained by the application of perturbation theory are compared to results evaluated from 3D simulations. Consequently, a suitability of using the perturbation theory is discussed