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We present a numerical method for iterative computation of electron optical systems influenced by space charge with an improved accuracy in the same calculation time. We replace the common algorithm for evaluating the space charge distribution with a new one based on the calculation of the current density distribution from an aberration polynomial. We introduce a re-meshing algorithm which adapts the mesh used for the field calculation by the finite element method in each iteration to the actual space charge distribution to keep it sufficiently fine in all areas with non-zero space charge.
Biological Science Symposia
B10 Multiscale Biological Imaging: From Micro to Macro — Animal to Clinical Models
The model of thermionic electron gun was developed. The Dirichlet problem for the cylinder (the Wehnelt electrode) restricted by two bottoms, one of them imitates a plane cathode and another imitates the equipotential surface, was solved analytically. It allows to study electron optical properties of the gun and its behaviour in dependence on Wehnelt potential for different cylinder depths. When the focal distance and the crossover size have the minimal value, this mode is called a work one. The crossover size and the beam half-angle values in this mode were approximated and the analytical method for electron gun calculation was developed.