Trajectory Tracer for Charged Particles Which Includes Magnetic Fields and Space Charge

Abstract

This paper presents the theory and design of an analog system for computing trajectories of charged particles in electron and ion guns, where the effects of space charge and magnetic fields are important. Two electrolytic tanks are used for simulation of the total electrostatic and magnetic fields. The wedge-shaped tank used for simulation of the electrostatic fields in axial symmetry contains current sources in the forms of wire probes and inlaid resistive plugs for the introduction of space-charge effects. The magnetic fields to be considered satisfy Laplace's equation and are simulated by specifying boundary conditions on the magnetic scalar potential. A special tank for obtaining accurate results on a thin annular beam is described. A precision analog computer solves the equations of motion with the fields measured in the tanks and controls the servomechanisms which move the field-sampling probes along the trajectory. Some results for high-perveance electron guns are compared with beam sampling measurements on actual guns.