Simulation of traveling-wave tube cold-test characteristics using MAFIA

The three-dimensional simulation code MAFIA4.0 was used to compute the cold-test parameters i.e. frequency-phase dispersion and the electron beam interaction impedance on the axis. The modeling code has high accuracy and will reduce TWT development time and cost. The quasi-periodic boundary condition can be used in MAFIA4.0 to calculate the eigen-frequency for each cavity´s phase shift. MAFIA was used to duplicate the perturbation experiment by simulating the CCTWT circuit cold test with a cylindrical dielectric rod. The interaction impedance can be derived from the difference between the eigen-frequency of the perturbed and that of unperturbed for the same setting phase shift. The on-axis interaction impedance also can be calculated directly using MAFIA by applying the quasi-periodic boundary condition. Excellent agreement between the experimental data and the simulation results was obtained.