Nonlinear, time-domain analysis of coupled-cavity traveling wave tubes

Coupled-cavity traveling wave tubes are used for radar and communication applications. The interaction structure is composed of a series of cavities that are connected via slots and a beam tunnel. Typically, the beam tunnel radius is a small fraction of the transverse cavity dimensions and is a negligible contributor to the cold circuit dispersion of the structure. As in many slow-wave devices, the flow of power in the structure is predominantly near the cavity walls and propagates from cavity to cavity through the slots. We describe a 2.5-D, hybrid, time-domain formulation where the structure is modeled by an equivalent circuit, but the electron beam is treated using models for the RF and magnetostatic fields and a Poisson solver for the space-charge fields. Electron dynamics are adapted from a previously-described time-domain helix TWT simulation code and are fully 3-D. The formulation implicitly includes several important physical processes needed to simulate CCTWTs.