Revised NASA Axiallv Symmetric Ring Model for Coupled- Cavi ty Traveling-Wave Tubes

A versatile large-signal, two-dimensional computer program is used by NASA to model coupled-cavity traveling-wave tubes (TWT’s). In this model, the electron beam is divided into a series of disks, each of which is further divided into axially symmetric rings which can expand and contract. The trajec-tories of the electron rings and the radiofrequency (RF) fields are determined from the calculated axial and radial space-charge, RF, and magnetic forces as the rings pass through a sequence of cavities. By varying electrical and geometric properties of individual cavities, the model is capable of simulating severs, velocity tapers, and voltage jumps. The calculated electron ring trajectories can be used in designing magnetic focusing and multidepressed collectors. The details of using the program are presented, and results are compared with experimental data