Electrostatic Analyzer with Variable Focal Length

Abstract

In the electrostatic analyzer of sector type with a given mean radius and a given openning angle, the focal length of the apparatus depends on the curvature of the central part of the equipotential line in the plane perpendicular to the beam. Therefore, an electrostatic analyzer with variable focal length may be proposed if the field shape near the central beam can be controled electrically without changing the geometry of the apparatus.
In this paper, a method of such a control is proposed and the variation of the field shape due to this method is described. A small 90° electrostatic analyzer with 162.5 mm mean radius was constructed and the focusing properties of this apparatus investigated. It was possible to focus a sharp radial image and a sharp axial image on a fluorescent screen at any location by the electrical control only.