Jean-Francois David

Efficient Time-Domain Simulations of a Helix Traveling-Wave Tube

An efficient time-domain discrete model of the interaction of an electron beam with an electromagnetic wave propagating in a slow-wave structure has been described by Kuznetsov. Using a projection of Maxwells equations onto the eigenmodes of the structure, the evolution of the entire electromagnetic field can be reduced to the evolution of its amplitude alone in each period of the waveguide. The number of degrees of freedom of the system is thus greatly reduced. This model has been successfully applied in the case of coupled-cavity traveling-wave tubes (TWTs) and can be applied to klystrons, where the circuit field is localized between the gaps of the cavities. In this paper, we present the results of numerical simulations performed by applying this model to a helix TWT. We show that the results obtained are in very good agreement with theory. We also compare our results with those from frequency-domain TWT simulation software.

Simulation of the BWO Threshold Current in a Helix TWT

The BWO threshold current of a helix TWT is simulated using the self-consistent 2.5D interaction code MVTRAD. The effect of different tube parameters on the threshold current is evaluated, and BWO countermeasures are investigated. The simulated results are compared to measurements

Backward-wave vacuum amplifier for THz amplification

Backward-wave regime is suitable for the realization of THz vacuum amplifiers. The advantages in terms of structure dimensions, losses and low beam voltage are demonstrated. A 1 THz backward-wave amplifier is presented showing more that 18 dB gain and 8.5 dBm output power.

Efficient 2.5-D non-stationary simulations of a helix TWT

An efficient non-stationary non-linear method, previously used to study the interaction in periodic coupled cavities traveling-wave tubes (TWT) in the one-dimensional case, is generalized to deal with periodic helix TWT and implemented in the 2.5-dimensional case via the development of a software. It is shown that the outputs of our program are in good agreement with the expected results and that the method employed allows to spare a lot of computational resources.

15.3: Design method for Double Corrugation Rectangular Waveguide THz vacuum amplifiers

A novel slow-wave structure (SWS), created for THz vacuum tubes, based on two parallel corrugations in a rectangular waveguide, realizes the conditions for a quasi-cylindrical field distribution, to support the interaction with a circular beam. A design method for THz TWT including the proposed SWS is presented based on a 2-D non-linear in-house code. Validation by 3-D particle-in-cells (PIC) simulator confirms the effectiveness of the method.

Simulation of multi-reflections in a helix-type TWT

A model of the reflections occurring at discontinuities in the delay-line of a helix-type traveling-wave tube (TWT) is being integrated into the interaction simulation code MVTRAD. First results are presented.

Hot matching conditions of coupled-cavity traveling-wave tubes

An analysis of the propagation characteristics of coupled-cavity (CC) delay lines in traveling-wave tubes (TWTs) under hot conditions is proposed. Using this approach a necessary impedance level at the end of the periodic line is derived that leads to minimum input reflections during operation. From this matching condition a required cold input reflection can be predicted which is in general different from the one commonly used.

Backward wave oscillator for THz frequency range based on double corrugation slow-wave structure

A 1-THz backward wave oscillator was designed and simulated. The introduction of the double corrugation rectangular waveguide SWS permits an effective interaction with cylindrical electron beams. The advantages of the backward wave operation permit remarkable performance up to 6 mW output power, in compact and realizable way, with a beam current density compatible with carbon nanotube cold cathode.

Space-TWT beam focusing including thermal electrons

The importance of taking into account thermal electrons when designing the beam optics of a TWT is shown on the example of Ku-Band space TWT with a high beam efficiency.

Large-Signal 2.5-D Steady-State Beam-Wave Interaction Simulation of Folded-Waveguide Traveling-Wave Tubes

A large-signal beam-wave interaction code for folded-waveguide traveling-wave tubes is presented. Formulation in frequency domain yields fast results of the steady state. The slow-wave structure is described by an equivalent circuit, while the electrons of the beam are modeled by means of a particle-in-cell approach. The latter exploits the periodicity of the electromagnetic fields in the beam tunnel region, thus allowing to work with a relatively low number of injected particles compared to conventional implementations. Physically consistent solutions are then obtained iteratively by incorporating the well-established Broydens method. Further improvement in terms of computation time is achieved by initializing the iterative algorithm with results from previous simulations. The approach is verified by a comparison with published interaction simulation results. Single-frequency responses are obtained within a few minutes, which compares favorably with other specialized simulation packages and enables device optimization with acceptable effort.