Accurate electron ray tracing for analysis of electron guns immersed in a magnetic-lens field

This paper describes an electron ray tracing method for calculating the electron trajectories and aberrations of electron guns immersed in a magnetic-lens field. Computation accuracy is improved by (1) solving the modified ray equation that the aberrations satisfy, (2) using the finite element method with third-order isoparametric elements for calculation of the electrostatic and magnetic fields, and (3) introducing the mesh subdivision method into the finite element method to treat the electron gun structure. Calculations of the aberrations, brightness, and emittance of a magnetic-lens-field-immersed gun demonstrate that the method is effective for analyzing and designing such guns.