THz Traveling Wave Tube Research Articles

Flatted Grating Folded Waveguide Slow Wave Structure for 0.2 THz Traveling Wave Tube

Flatted Grating Folded Waveguide Slow Wave Structure for 0.2 THz Traveling Wave Tube

Design and Analysis of Electron Beam of 0.67 THz Traveling Wave Tube

Design and Analysis of Electron Beam of 0.67 THz Traveling Wave Tube

Design and development of a sheet-beam electron gun with large current for a THz traveling-wave tube

Design and development of a sheet-beam electron gun with large current for a THz traveling-wave tube

Analysis of the high-frequency characteristics of a sine waveguide

Based on the double-periodic characteristics of a sine waveguide, the dispersion equation, interaction impedance, and transmission losses of slow-wave structures are derived. The dispersion equation indicates that the waves propagating in the sine waveguide should belong to two mode types, which can exist independently rather than as “pseudo-modes.” The dispersion equation, interaction impedance, and transmission losses are obtained using a theoretical model. A 220 GHz traveling wave tube (TWT) is used as an illustrative example to verify the validity of the analytical model. The calculated results show that the dispersion curve is in good agreement with that given by the Ansys high-frequency simulation software over the entire frequency range and that the theoretical numerical calculation time is less than 2% of that of the Ansys software package. In addition, the results demonstrate that the interaction impedance of the symmetric φ0 + π mode is much higher than that of the asymmetric φ0 mode. Therefore, the symmetric φ0 + π mode should be used for propagation in sine waveguide traveling-wave tubes. Moreover, when the conductivity is set at 1.6 × 107 S/m, the loss of the sine waveguide is ∼1.15 dB/cm for 220 GHz. The equivalent conductivity of the metal can be used appropriately in the design of the mm-wave and the THz TWT.

Study of Beam–Wave Interaction in a Sub-THz Traveling Wave Tube with a Converging Sheet Electron Beam Focused by a Uniform Magnetic Field

A traveling-wave tube (TWT) with a sheet electron beam and staggered double-grating slow-wave structure (SWS) is a promising high-power, wideband terahertz amplifier. In such tubes, electron-optical systems (EOSs) with a converging sheet beam are mostly used, which allow a reduction of the cathode load, increase the lifetime, and enable operation in a continuous-wave (CW) mode. This paper presents the results of a 3D particle-in-cell (PIC) simulation of the 0.22 THz TWT driven with a converged sheet beam, which is compressed to less than 100 μm thickness in the EOS with a magnetically shielded cathode. The beam with high compression has a significant transversal velocity spread and essentially non-uniform current density distribution over the cross-section. These factors significantly affect the beam–wave interaction. We compare the performance of the TWT driven by the compressed sheet beam and by an idealized initially rectilinear beam without any velocity spread.

Sheet Electron Optical System for a 1.03-THz Traveling-Wave Tube

The electron optical systems (EOS) play a vital role in vacuum electron devices (VED). This letter reported the design and experiments of the sheet EOS for the 1.03 THz traveling wave tube (TWT). A high-current-density sheet electron beam (SEB) electron gun generating up to 20.3-mA at 22.4-kV is designed, based on the requirements of this TWT. Due to the very high operating frequency, more than 1 THz, the miniature tunnel and beam waist with a dimension of 0.05 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> 0.148 mm and 0.025 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> 0.114 mm, respectively, will lead to a very high beam current density (906.9 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). Therefore, a 1-Telsa uniform magnetic system is designed, to ensure such a high-current-density SEB passes through the 27-mm tunnel. Finally, the primary experiments indicate that 7.56-mA current reaches the collector.

Amplification of THz waves by beam-wave interaction in self-assembled helical slow-wave structures with single and double chirality

We investigate the interaction between an electron beam and a THz guided electromagnetic wave in a helical slow-wave structure formed by self-assembly of a conductive ribbon. We have previously shown the controlled fabrication of this slow-wave structure and its potential to form the basis for widely deployable millimeter-through-THz traveling-wave tube amplifiers. The process allows the fabrication of helical slow-wave structures with single and double chirality. Here, we use three-dimensional simulations to perform a comparative analysis of beam–wave interaction in self-assembled gold helices with single and double chirality. First, the structures are modeled without the electron beam (cold helices) to calculate the distribution of the electric field generated by the high-frequency wave. We perform simulations of cold helices by using Computer Simulation Technology Microwave Studio. Second, we evaluate the interaction between an electron beam and the THz travelingwave by using a particle in cell simulator in Computer Simulation Technology Particle Studio. Simulation studies show that a switch in chirality in the middle of self-assembled helices generates a reflected wave that boosts beam–wave interaction. We demonstrate that this efficient energy exchange will potentially provide high gain in THz traveling-wave tube amplifiers based on self-assembled helices.

Terahertz Power Module Based on 0.34 THz Traveling Wave Tube

A terahertz power module (TPM) based on 0.34 THz traveling wave tube (TWT) is described. A novel modified staggered double vane (SDV) slow wave structure (SWS) is employed in the TWT to realize broad bandwidth. This device provides an output power over 1 W and a gain over 18 dB from 0.33 THz to 0.355 THz. Although the available solid-state signal source is unable to drive the TPM to saturation, a maximum 1.6 W output power and 22 dB gain have been measured. The power dissipation of the TPM is 100 W and is cooled by conduction. It is a promising solution of power amplifiers for terahertz wireless communication.

Systematic Design Study of the Elliptical Sheet Beam Electron Gun for Terahertz TWT Applications

The design methodology of a sheet beam electron gun has been discussed and, subsequently, used for the design of a gun intended for use in a 0.3 THz traveling wave tube amplifier. The initial gun design parameters have been calculated analytically using a theoretical approach. Then, starting with these calculated parameters, the designed gun is then simulated using a commercial 3-D simulation code “CST Particle Studio” and optimized to get the target beam parameters. The circular-shaped cathode with an elliptically shaped beam-focusing electrode and elliptically shaped anode has been used to produce the good laminar elliptical sheet beam. The effect of varying the several parameters, such as height, width, and distance of focusing electrode, cathode-anode distance, and anode height have been studied to investigate their sensitivity on the target beam parameters. The simulation results predict that the designed sheet beam electron gun produces an elliptical beam with a desired beam cross section of 0.33 mm × 0.066 mm at a beam-waist position of 6.61 mm from the curved cathode emission surface corresponding to the beam parameters of 12 kV beam voltage and 55 mA beam current.

Full-wave analysis of the high frequency characteristics of the sine waveguide slow-wave structure

A theoretical model for calculation of the high frequency characteristics of the sine waveguide slow-wave structure (SWS) is proposed. The formulas of dispersion and interaction impedances of the hybrid modes are obtained by combining the Helmholtz equation with the appropriate boundary conditions. Using the full wave analysis method, it is proved that the periodic structures with a half-period shift followed leads to a pairwise closing of passbands characteristic of adjacent mode. The sine waveguide SWS for 0.22THz traveling wave tube (TWT) is chosen as an illustrative example to verify the validity of the theoretical model, and the calculation results of the dispersion curve and interaction impedance curve are consistent with the HFSS simulation results. In addition, the influences of dimensions of sine waveguide on the high frequency characteristics of +1st spatial harmonic wave are investigated by numerical calculation. The study indicates that the appropriate SWS parameters are helpful for improving the bandwidth and increasing output power of TWT.

Three dimensional nonlinear analysis of a single-grating rectangular waveguide Cerenkov maser

A three dimensional (3-D) nonlinear model for illustrating the beam-wave interaction in a single-grating rectangular waveguide sheet-beam Cerenkov maser is presented. The dynamical equations and the equations of motion are solved self-consistently to predict the device performance. Space-charge effects and Ohmic losses are considered in the model. A 1.03 THz backward wave oscillator and a 0.65 THz traveling wave tube are discussed as two illustrative examples.

Theoretical and simulation study of 0.14 THz fundamental mode multi-beam folded waveguide traveling wave tube

To improve the current and output power of the THz traveling wave tube (TWT), a fundamental mode multi-beam folded waveguide (FMMBFW) TWT scheme is proposed. Firstly, an equivalent circuit model FMMBFW for calculating the high-frequency characteristic is established and compared with numerical simulation. Secondly, the transmission characteristic of 60 periods FMMBFW is analyzed. Finally, the beam-wave interaction characteristic of 0.14 THz FMMBFW TWT is completed by numerical simulation and theoretical calculation. When the DC current is 12 mA and the applied voltage is 15.75 kV, the 3 dB bandwidth of 0.14 THz FMMBFW TWT is 25 GHz (128-153 GHz), the maximum gain is 33.61 dB and the maximum output power is 23 W. When the DC current is 30 mA and the voltage is 15.75 kV, the maximum gain is 38 dB and the maximum pulse output power is 63.1 W at 0.14 THz. Compared with the fundamental single-beam folded waveguide (FW) TWT under the same working condition, the 3 dB bandwidth is doubled, its output power is raised by a factor of 9.66 and the interaction efficiency is increased by 3.22 times. Based on the same gain, the length of FMMBFW TWT is just 52.6 mm while the length of single beam FW-TWT is 78.2 mm. The proposed method can increase effectively the current of FMMBFW TWT; and the interaction gain, efficiency, 3 dB bandwidth, output power can be improved. When the gain is the same, a shorted and compact FMMBFW TWT can be constucuted.

Low perveance confined-flow Pierce gun for a 0.14 THz broadband folded waveguide traveling wave tube

An approach for designing an electron gun for a high efficiency, high linearity 0.14 THz traveling wave tube (TWT), has been presented. A Pierce electron gun of beam perveance 0.0047 μP has been designed for a high gain, high linearity and high efficiency 0.14 THz TWT using CST STUDIO SUITE Charged Particle Simulation soft and electronic optical software TAU. The initial gun geometry, as obtained from the Vaughan iterative synthesis method, has been used as input for simulation of the electron gun. An M-type dispenser cathode of diameter 0.8 mm has been used for cathode loading of 2.75 A/cm 2. The magnetic focusing with integral-pole-piece barrel assembly and periodic-permanent magnets (PPM) have been designed using CST and TAU. The practical problem of linking requisite cathode flux to the cathode for confined flow of the electron beam with low convergence factor has been sorted out by gradually increasing the PPM magnetic field. The magnetic field has been increased in steps from the gun and over the first five magnets varying from Brillouin field ( B B) value to twice B B for achieving the electron beam with scalloping less than 10%. Simulation results show that the design method is reasonable for obtaining a 0.14 THz TWT electron gun and periodic-permanent magnets (PPM).