Microscopy and Microanalysis: Volume 21 -

Simulation of Space Charge Effects in Electron Optical System Based on the Calculations of Current Density
Jiří Zelinka, Martin Oral, Tomáš Radlička
Published online by Cambridge University Press:

28 September 2015, pp. 246-251
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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.

Analytical Method for Electron Gun Calculation
Oleg D. Potapkin
Published online by Cambridge University Press:

28 September 2015, pp. 252-257
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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.

Microscopy and Microanalysis