Computer programs for designing multipole electron and ion optical systems

Abstract

New computer programs have been developed for designing multipole electron and ion beam systems. The charge density method is used to calculate the axial field distribution for electrostatic quadrupole and octopole lenses and deflectors, dipole deflectors, and rotated magnetic quadrupole lenses. The programs are described and some comparisons against analytic models are presented. An existing finite element program is used so that electrostatic round lenses may also be included in the analysis. An optical properties program uses a new compact aberration theory developed by the authors to calculate the first‐order focusing and deflection properties, third‐order geometrical and first‐order chromatic aberrations, for any combination of the elements already mentioned. The desired focusing is obtained by using an iterative least squares routine to focus the round and quadrupole lenses. An analysis of crossed electrostatic and magnetic quadrupole lenses is presented showing how the first‐order axial chromatic aberration coefficient can be reduced to less than 0.1 mm, making the size of the chromatic disk negligible.