Ray tracing on the electron optical bench

In the design of electrostatic lenses, a rapid and reliable method of determining electron trajectories is required. This paper describes a demountable vacuum system incorporating an electron gun, deflection plates, clyindrical lenses and a pair of phosphor coated mesh structures. The various parts are assembled on heavy bases which rest on precision ground and graduated glass rods. A vacuum sealed push-rod permits adjusting the relative positions of the lenses during testing. The electron beam passes through the parallel phosphor coated meshes and the lighted spots are observed by means of a cathodometer to determine beam landing angle. The complete device thus provides a tool for measuring not only the effects of changing the potentials of electrostatic lens elements but of changing their relative positions as well during a single test. The complete system is called an "electron optical bench" and also includes a simple 9 × 9 dot pattern generator. The pattern of dots viewed on the phosphor meshes will quickly reveal aberration due to lens distortion.