On the Focusing of High-Current Electron Beams

The focusing of high-current electron beams by means of a system of periodically spaced magnetic lenses has been studied. The trajectories of the electrons under the influence of magnetic and space charge forces have been obtained by the use of an analog computer. Graphs have been prepared which permit the design of a lens focusing system for given values of current, voltage, and beam diameter. The solutions are obtained for the Glaser magnetic lens with longitudinal field variation of the form Bz=B0(1+(z/a)2)[minus]1. The conditions of operation appropriate to the minimum chromatic aberration are obtained, and the entrance conditions to the lens system discussed.