Traveling wave tubes are rapidly evolving to provide unprecedented power level in comparison to solid state devices in the millimeter waves region of the spectrum (80–300 GHz) thus enabling a wide ...

https://www.tandfonline.com/doi/pdf/10.1080/09205071.2020.1848643

Millimeter wave traveling wave tubes for the 21st Century

A novel slow wave structure (SWS), called double tunnel staggered grating (DTSG), which originates from the double staggered grating (DSG) and folded waveguide (FW), is proposed to develop a dual-beam traveling wave tube (TWT) with high power and electron efficiency in Terahertz (THz) band. Using two key techniques: (1) the rectangular holes are opened in the grating-ridges, and the operating mode is cut-off at holes; (2) specific grating-height, the DTSG-SWS possesses the wide operating band as DSG-SWS, high interaction impedance as the rectangular grating (RG) SWS, and good transmission characteristics as FW-SWS. In addition, it is not only suitable for the dual-beam TWT, but also is simple and easy of fabrication as DSG-SWS. The particle-in-cell simulation analysis confirms that the saturated power and electron efficiency of TWT using DTSG-SWS have been significantly improved compared with the TWT using DSG-SWS.

Novel Double Tunnel Staggered Grating Slow Wave Structure for 0.2 THz Traveling Wave Tube

We present a novel slow-wave structure (SWS) to significantly enhance the performance of high-power backward wave oscillators (BWOs). The design features a periodic metallic ring insertion and a deeply corrugated cylindrical waveguide. Both serving to improve interaction impedance and flexibility in dispersion curve engineering. A new technique for mode control in waveguides is also introduced. In addition to demonstrating mode control in SWSs, the key aspects of the presented design are mode dominance reversal and a 100% improvement in interaction impedance that can be exploited to achieve greater power conversion efficiency and output mode purity. Performance comparisons on group velocity, phase velocity and interaction impedance of the new SWS versus the conventional corrugated waveguide are provided. We extend the concept of inhomogeneous SWSs by designing a three-section inhomogeneous SWS. Further simulations using a Particle in Cell code of a highly efficient three-section inhomogeneous K
 a
-band BWO generates a peak output power of a 5.92 MW at 27 GHz with a 58% peak efficiency.

A Novel Slow-Wave Structure for High-Power $K_{a}$ -Band Backward Wave Oscillators With Mode Control

Particle simulation and experimental results are presented about a Ka-band overmoded Cherenkov-type high power millimeter wave generator in this paper. The relativistic electron beam with peak current of 8.4 kA was generated by a pulsed power accelerator working at the voltage of 625 kV, which was guided by an axial magnetic field of 1.05 T and transported through the beam-wave interaction structures. After careful calibration, the microwave power radiated in the far field was as high as about 500 MW, with a frequency of 32.1 GHz and a pulse width of 20 ns. The radiation mode was well controlled to be TM(0n) mode.

Gigawatt-class radiation generated by a Ka-band overmoded Cherenkov-type high power millimeter wave generator

The advances of high-frequency vacuum electron devices (VEDs) in China are reviewed in this paper, including traveling-wave tubes (TWTs) based on novel slow-wave structures (SWSs), high harmonic TWT amplifier, gyrotrons, Smith–Purcell (SP) radiation sources, surface plasmon polaritons (SPPs) sources, and terahertz (THz) radiation sources in ion-focused beam-plasma system. As one of the most widely used VEDs, TWTs based on folded type SWSs, planar SWSs, and grating type SWSs are studied theoretically and experimentally from Ka -band to R -band. Using folded type SWSs, two TWT amplifiers are developed. As high-power millimeter wave and THz wave sources, gyrotron TWTs, gyrotron oscillators, and gyroklystrons are presented. Moreover, this paper shows SP radiation sources, SPPs sources, and THz radiation sources in ion-focused beam-plasma system open good prospects for developing high-frequency VEDs with new mechanisms, which undoubtedly brings about innovative changes for the development of VEDs.

Some Advances in Theory and Experiment of High-Frequency Vacuum Electron Devices in China

It is attractive to use sheet beam vacuum devices to generate high frequency, high-power microwave radiation. In this paper, we present the numerical and experimental studies of a high-power Ka-band sheet electron beam backward wave oscillator (BWO), in which the double-grating rectangular waveguide is used as the slow wave structure (SWS) for its thermal and mechanical robustness. The fundamental mode of this kind of SWS is an antisymmetric mode which has an antisymmetric longitudinal field distribution and will nonsynchronously interact with the electron beam on two sides of the electron channel along the vertical direction. We put forward a method to overcome this trouble in this paper. To drive this BWO, a high-power sheet beam is used with a cross section of 30 mm $\times\,$ 1 mm. A thin graphite cathode is used for its superiority in producing a high current, high-quality electron beam. For an experimental electron beam of 141 kV and 1668 A, the output power of over 46.8 MW at 31.68 GHz is obtained, which corresponds to a beam–wave interaction efficiency of 19.9%. Compared with the conventional hollow beam BWO and the single-grating rectangular waveguide sheet beam BWO, the double-grating sheet beam BWOs efficiency is higher, which indicates that the double-grating sheet beam device is promising for producing millimeter wave radiation with high power and high efficiency.

Study of High-Power Ka-Band Rectangular Double-Grating Sheet Beam BWO

In this paper, a high-power Ka-band traveling-wave tube (TWT) driven by a sheet electron beam is proposed and demonstrated by means of the simulation and experimental methods. The single grating rectangular waveguide with large width-to-height ratio is used as the slow-wave structure (SWS). An $E$ -plane bend energy coupler is put forward to feed this wide SWS. An irregular transition structure between the input waveguide and the SWS is suggested and designed, which is beneficial to suppress the self-excited oscillation. For a practical electron beam (20 mm $\times \,\, 1$ mm, 150.1 kV, 850 A, and 20-ns), the output power of this single rectangular grating sheet beam TWT is larger than 750 kW from 34.5 to 35.4 GHz. The maximum power is 1.21 MW at 35 GHz, corresponding to a gain of 20.4 dB.

A High-Power Single Rectangular Grating Sheet Electron Beam Traveling-Wave Tube

The dispersion equation and interaction impedance of the ridge-loaded ring-plane slow-wave structure are obtained, by application of the Ritz-Galerkin method. Numerical results are given in terms of k-/spl nu//sub p/ curves and impedance diagrams. The influence of several geometrical dimensions on the dispersion characteristic and interaction impedance are discussed. This kind of slow-wave circuit can operate at a high power level over a relatively wide microwave-frequency range. To get higher power and broader bandwidth for this circuit the optimum opening angle and a smaller radius of the loaded ridge must be chosen. The paper provides the theoretical basis for designing this type of slow-wave circuit for high-power travelling-wave tubes.

Theoretical analysis of ridge-loaded ring-plane slow wave structure by variational methods

Simulation Strategies for ReaxFF Molecular Dynamics in Coal Pyrolysis Applications: A Review

In order to improve the output power of terahertz traveling-wave tubes (TWTs), a slow wave structure (SWS) named arbitrary staggered multi-vane slow wave structure is proposed in this paper. The SWS is suitable for the double sheet electron beams operation, and there is no coupling between the double electron beams. Based on this kind of SWS, a high-power 220 GHz TWT driven by the double electron beam is investigated. A suitable Y-branch waveguide is put forward to overcome the difficulties for designing the input/output structure of this double beam traveling-wave tubes (DBTWTs).

Shuaihong Liu

Papers

Study of High-Power Ka-Band Rectangular Double-Grating Sheet Beam BWO

A High-Power Single Rectangular Grating Sheet Electron Beam Traveling-Wave Tube

Theoretical analysis of ridge-loaded ring-plane slow wave structure by variational methods

Simulation Strategies for ReaxFF Molecular Dynamics in Coal Pyrolysis Applications: A Review

An arbitrary staggered multi-vane traveling wave tube driven by double sheet electron beams