Three-dimensional, time-dependent simulation of coupled-cavity TWTs

Summary form only given. We report on the development of a three-dimensional, time-dependent simulation code for coupled-cavity TWTs. The cavities are modeled using the Curnow equivalent circuit that has been generalized to include resistive loading. Benchmarks of the circuit model with production tubes and with the three-dimensional electromagnetic field solver CTLSS are described. A set of seven first order differential equations per cavity are obtained to describe circuit currents and voltages in each cavity. These equations are integrated in time simultaneously with the Lorentz force equations for each electron contained within the structure. The initial model for the circuit fields experienced by the electrons follows the development of Kosmahl and Branch, however, later versions of the code will incorporate the field structure obtained using CTLSS. Two space-charge algorithms are used: a three-dimensional Helmholtz field representation, and a two-dimensional Poisson solver. A comparison of the two- and three-dimensional space-charge algorithms is discussed with particular attention to the regimes of validity of the two-dimensional Poisson solver.