Circular-Beam Ray Tracing on a Microcomputer

A computer code is described that traces charged particles through a system of electrostatic and magnetic solenoid lenses. This code requires symmetry about the beam axis, but it incorporates a useful approximation for handling beam emittance and variable space-charge neutralization. It features a friendly and versatile user interface and runs efficiently on an Apple II microcomputer. There are a number of both ray-tracing and matrix beam-transport codes available for simulating particle-beam focusing and transport systems. The popular, linear code TRACE, for example, is a versatile simulation code that can trace outer beam profiles through a variety of both accelerating and transport structures. TRACE provides a first-order approximation for external fields, space charge, and beam emittance. Because the code is so common and runs relatively quickly, it is a valuable tool for checking performance of various designs. However, I wanted a small and simple code that could run on a readily available microcomputer and that would be more interactive than many existing codes. To keep the new code short and simple, it had to be somewhat limited in versatility. The major restriction is that the beam profile must be circularly symmetric, which eliminates quadrupole transport but allows simulation of a useful variety of electrostatic and solenoidal focusing systems.