Two-dimensional small-angle deflection theory

The aberrations resulting from the deflection of an electron beam by two similar, mutually perpendicular magnetic fields have been evaluated. The beam is assumed to be composed of noninteracting, nonrelativistic particles converging, when undeflected, to a single point in the center of the target. If dynamic focusing is used, the field shapes can be adjusted to eliminate astigmatism and minimize coma. Field optimization procedures are presented with a numerical example. The correct densities and boundaries are recorded by a computer-controlled plotter.