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In this paper, a novel Eulerian nonlinear beam-wave interaction (BWI) theory considering harmonic interaction of a helix traveling-wave tube (TWT) is developed. Derived from this Eulerian model, the novel Eulerian nonlinear analytic solutions (the fourth-order analytic solution of fundamental and the second-order analytic solution of harmonic) are first obtained by the method of successive approximation. The analytic relationships between electric fields of fundamental/harmonic frequencies and electron phases are also found. Then, the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory are compared to a Lagrangian theory. C-band and Ku-band helix TWTs based on a single pitch section are included in the simulation. It is found that the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory agree well with the Lagrangian theory at 1-dB gain compression point. Interestingly, the saturation effects caused by electron overtaking cannot be found by the traditional Eulerian analysis but can be described by the Eulerian nonlinear analytic solutions and Eulerian nonlinear BWI theory. Moreover, Eulerian nonlinear analytic solutions are simpler and more accurately than existing approaches and, thus, allow analytical progress. This paper confirms that the Eulerian nonlinear analytic solutions can outperform the previous proposals.

In this paper, the fourth-order analytic solution of amplitude modulation to phase modulation (AM/PM) conversion is first derived from an Eulerian nonlinear analytic model. The analytic relationships between electron phases, detuning parameter b, and AM/PM conversion are also found. Then, the mechanism of AM/PM conversion is studied. It is found that the generation of the harmonics in the dc component of the electron phase in the nonlinear beam–wave interaction region is the main mechanism of AM/PM conversion. Next, a series of AM/PM conversion suppression schemes is discussed by using the mechanism. The Eulerian formations are validated by an in-house code based on the Lagrangian theory. Results show that the fourth-order analytic solution of normalized axial electric field and AM/PM conversion agree well with the Lagrangian theory in the nonlinear region. In addition, the suppression schemes are applied to a high-efficiency Ku-band space traveling-wave tube (TWT). The AM/PM conversion distortion is greatly reduced by approximately 50% with a slight drop of output power. We hope that our efforts will help the nonlinear design of TWT in the future.

The assembly distance between cathode and heater has significant influence on the performance of electron gun of traveling wave tubes. This paper presents a simulation method to accurately determine this assembly distance. The simulation method uses ANSYS to simulate the working state of electron gun, and transfers the thermally deformed cathode and heater models into CST through the ANSYS geometry processing module SpaceClaim. Use the contact judgment function of CST to gradually move the heater to contact the cathode to measure the distance between cathode and heater. Adjust the model on the basis of measuring results and continue simulation process until the assembly distance which satisfies the assembly tolerance rate is obtained. This method can accurately measure the distance between cathode and heater after deformation, avoid damage of electron gun under working condition and effectively guide the assembly process of electron gun.

This paper proposes a steady-state theoretical model for the klystron beam-wave interaction and develops the relevant code. First, the electron beam channel and the resonant cavity are expanded in a mode, and the equations satisfying the voltage and current of the electron beam channel and the resonant cavity in the steady state are derived, and then the corresponding field distribution is obtained for solving the electron motion equation. Taking an X-band klystron simulation design as an example, the calculation ability and effect of the program are tested. The results are comparable to the 3D PIC software, and the calculation efficiency is greatly improved. The preliminary design and parameter optimization of the beam-wave interaction system.

Assembly process and key parameters have important effects on performance of traveling wave tubes. In this paper, simulation exploration on Graphite heat extrusion process and the cathode-heater assembly distance of electron gun are introduced, which have been carried out during the last two years and is to be used to guide the assembly process in TWT. More simulation exploration in processing are still in progress.

This paper describes the working and dispersion synchronization condition of the novel beam-wave interaction to develop a watts-level, tunable THz amplifier, which can enhance the gain and reduce the starting current. In the feedback circuit, two beams can be possibly coupled with HOM as their beam position has a strong coupling with the modes. Thus, the HOM is analyzed. Simulation results show that the high order mode excitation cannot become dominant in the feedback circuit.

In order to suppress the dynamic defocusing problem of the electron beam that often occurs in high-efficiency space TWT, this paper provides an effective focusing magnetic field design method and takes a traveling wave tube of a certain band as an example to introduce and explain. Under the premise of not affecting other working indexes, the focusing magnetic field designed by this method effectively suppresses its dynamic defocusing problem.

This paper proposes a fast optimization design method for the traveling wave tube (TWT) periodic permanent magnet focusing (PPM) system. Based on the target system value distribution using MTSS software, a magnetic system that satisfies the requirements is quickly designed, and the accurate single-loop value of each magnetic steel is obtained. The actual magnetic system processed according to the single-loop value is more in line with the design requirements, which is conducive to the assembly and commissioning of higher frequency millimeter wave and terahertz electric vacuum devices.

As it is well known that the simplified classical Pierce’s three-wave theory can provide scaling insights into traveling-wave tube (TWT) operation for its close-form solutions, and thus becomes a useful guide for TWT design. However, the classical Pierce’s three-wave theory shows poor agreement with Lagrangian theory, so determining how to achieve a more accurately Pierce’s three-wave theory from Pierce’s four-wave theory becomes an open problem. In this paper, a more accurately revised Pierce’s three-wave dispersion relation is deduced by using an approximate treatment on the nonlinear term of the dispersion relation of Pierce’s four-wave beam-wave interaction theory. Meanwhile, the boundary conditions of classical Pierce’s three-wave theory are revised by theoretical analysis. Thus, the revised Pierce’s three-wave theory is established. The Pierce small-signal theories are compared to each other and Lagrangian theory on a set of TWT parameters which are based on a single pitch section of C- and Ku- bands TWTs. It is found that the revised Pierce’s three-wave theory agrees extremely well with Lagrangian theory and gains more accuracy than the classical Pierce’s three-wave theory in the small-signal beam-wave interaction region. Finally, the phase difference between Pierce’s four-wave theory and revised Pierce’s three-wave theory is discussed.

In this paper, a MATLAB program of the nonlinear theoretical calculation based on a 1-D electron model for the Ka-band sheet beam extended interaction oscillator (SBEIO) is presented. The optimized electric field distribution with a high output power has been gained by the MATLAB program and the simulated annealing (SA) algorithm. The structure of the high-frequency cavity with a high output power and high efficiency, has been designed, corresponding the optimized optimized electric field distribution. In the simulation, the proposed SBEIO produces a 32.S-kW output power, 27% efficiency in a stable operating condition.

The study and experimental studies of a 6 kW W-band PCM focused high power sheet beam extended interaction oscillator are firstly reported. The initial hot test results show a 6 kW maximum output peak power with a 47.2 kV and 2.1 A beam. An average power of 1.2 kW is obtained with a 20% working duty. The stable operation shows a much higher potential average power capability. A new designed PCM magnet is applied in the beam focusing. It presents a 99% static beam transmission and 94.4% beam transmission with saturated RF interaction. The overall dimensions and weight of the SBEIO are 400×100×60 mm and 7 kg.

Group delay is an important parameter to evaluate the performance of space traveling wave tubes. In this paper, a positive-tapered pitch profile is introduced in the input segment and the length of the second segment is slightly adjusted to optimize the group delay performance of a L-band space TWT. Using this method, the group delay is finally successfully reduced to less than 1ns without loss of gain. The optimization is fulfilled in Microwave Tube Simulator Suite.

A simulation method of Graphite Heat Extrusion Process for high-frequency structure of helix STWT is proposed in this paper. The Graphite Heat Extrusion Process includes both the heating and the cooling process which cannot be simulated in a whole simulation, so we simulate them respectively in ANSYS Workbench. The model after heating is somewhat damaged and need to be repaired in ANSYS Workbench. The effects of the deformation on electrical characteristics of the high-frequency structure can be analyzed with Microwave Tube Simulator Suite (MTSS). Using this method, the working parameters of the Graphite Heat Extrusion Process can be evaluated, as well the performance of the manufactured high-frequency structure can be observed.

The beam-wave interaction efficiency of sheet beam traveling-wave tube (SBTWT) has an intense relevance to the length of RF circuit. A matlab code based on the large-signal theory has been developed to investigate the relationship between the efficiency and RF circuit length. The 3D CST-PIC (Particle in Cell) simulations in a Ka band sheet beam TWT are performed to verify the calculations. The results generated by PIC and the code are both presented below.

An novel heater structure capable of providing higher heating efficiency is designed. A method is proposed to equate the thermal resistance that occurs during the actual assembly process. The thermal and structural analysis of the sheet beam gun are completed using the finite element code ANSYS. The new structure reduces heating power by 50% (31.6 W to 15.9 W) at a cathode temperature of 1100 °C and also shows better performance in thermal deformation than the previous one.