Large-signal theory and simulation of gyrotron traveling-wave amplifiers

A new simulation code, MODEL, is presented that is general in the device configurations and operational conditions it may represent, flexible as far as the possible research applications, and highly accurate in its internal calculations and as compared to experimental results. MODEL is based on a coupled-mode transmission-line formulation for the RF fields and an electron beam model featuring a slow variable formulation and a general dc magnetic field profile. These analytic theories are combined to form a self-consistent large signal theory of the gyrotron traveling-wave amplifier (GTWA) describing the gyrotron interaction between an arbitrary TE RF mode and the s{dollar}sp{lcub}rm th{rcub}{dollar} cyclotron harmonic of an electron beam. This analytic theory and its numerical implementation describe physical effects not represented in previous simulation efforts, and MODEL thus increases the simulation-based research capability of researchers studying GTWA devices. MODEL has the ability to represent physical boundary conditions, including the effects of electrically nonideal waveguide walls and tapered waveguide walls, and to simulate the below-cutoff portion of the interaction in reverse injection type GTWA devices. MODEL has undergone an extensive verification process against published simulation results and published and unpublished experimental results. The various attributes of MODEL make it useful for study of the basic gyrotron interaction, design/optimization studies, and the explanation/interpretation of observed physical behaviors.