A Critical Assessment of the Finite Element Method for Calculating Magnetic Fields in Electron Optics

  • Khadija B.M. Tahir

    Student thesis: Doctoral ThesisDoctor of Philosophy

    Abstract

    The present investigation is concerned with the determination of the magnetic field distribution in magnetic electron lenses by means of the finite element method. A critical comparison is made of the
    available finite element computer programs. Necessary modifications
    have been made in certain programs, useful comments and general data format were written for two recently developed programs.

    Special attention has been paid to those factors that affect the
    efficiency of the finite element method in camputer aided design of
    magnetic electron lenses. These include the correct choice of
    boundary conditions. Another important factor investigated is the
    influence of mesh layout for the subsequent finite element
    calculations.

    By recomputing several examples of lenses found in the literature,
    discrepancies of up to 30% were reduced, resulting in excellent
    agreement with the associated experimental results, simply by
    rearranging the mesh layout in a more convenient way. Through a more systematic application of the finite element method, several
    misleading conclusions to be found in the literature were detected.
    Some of these conclusions arose from the finite element method itself,as previously mentioned. Other misleading conclusions were also
    discovered that were not due to the finite element method but to design errors in the lens itself.

    A study has been made of the errors in lens design including the
    inadequate thickness of iron shrouds etc.
    Date of AwardNov 1985
    Original languageEnglish
    Awarding Institution
    • Aston University

    Keywords

    • critical assessment
    • finite element method
    • magnetic fields
    • electron optics

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