The present Ph.D. report deals with the time-domain modeling and simulation of the beam-wave interaction that occurs in helix traveling-wave tubes (TWTs) amplifiers. The TWT is an over-sized device, and so the non-stationary general software that is sometimes used in order to simulate a device is generally time consuming. As a consequence, it should not be used for Thales design activities. Therefore, 'specialized' models must be used. This Ph.D. is about S. Kuznetsov's non-stationary discrete model of excitation of a periodic waveguide. Before our works started, it has been demonstrated (N. Ryskin et al., 2007) that this model can be applied in order to simulate coupled-cavities TWTs in one dimension. However, the application of this model to higher dimensions problems and for other types of devices had never been studied. During this Ph.D., we proved that the discrete model can be applied to helix TWTs in one and two dimensions via the development of simulation codes (HelL-1D and HelL-2D). Finally, we developped a model's improvement that permits to quantitatively control the wave reflexion phenomena at the ends of the delay line. This improvement is important for the practical time-domain simulation of the TWT by using Kuznetsov's discrete model.
