Determination of the Optimum Electrode Shape of Electrostatic Einzel Lenses

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Abstract
A practical method of determining the optimum electrode shape of einzel lenses is discussed for ion microprobe applications: both the spherical and chromatic aberrations contribute, and the focal length is relatively long. A new variable D * is introduced to express the relative aberration effect at the optimum lens design, and the values of D * for the various electrode shapes are compared. The method is applied to typical electrode shapes, and the superiority of an asymmetric electrode shape with respect to the center electrode is shown.