In this article, a 1-THz traveling-wave tube (TWT) based on flat-roofed sine waveguide (SWG) slow wave structure (SWS) has been studied theoretically and experimentally, and parts of the component have been fabricated. First, the flat-roofed SWG SWS has been optimized for working at 1 THz, the normalized phase velocity is around 0.287, and the interaction impedance is over 3.5 Ω in the frequency range of 1.02-1.04 THz. Meanwhile, the performance of the designed TWT has been simulated, whose saturated output power is 720 mW and the corresponding gain is 28.57 dB. What is more, to decrease the transmission loss of the high-frequency structure, the input and output structures have been designed and a transition structure that transforms the waveguide to standard rectangular waveguide has been proposed. The simulation results show that the reflection coefficient of the novel proposed transmission system is less than -20 dB, and the insertion losses of the transition structure with the input and output waveguides are 2.45 and 1.68 dB, respectively. Finally, the designed SWS has been fabricated by deep reactive-ion etching (DRIE) and tested; S ₁₁ is generally less than -10 dB in the frequency range of 1020-1040 GHz.

We propose and experimentally demonstrate a high-power and wide-bandwidth terahertz travelling wave tube (TWT), which is with two cascade amplification sections: the output wave of the first TWT is used as the input of the second one. Using a 17 kV, 71 mA electron beam, the measured peak power is over 60 watt and the average output power is over 12 watts with 20% duty cycle at the frequency around 0.22 THz. The gain is about 30 dB and the bandwidth is over 6 GHz. The average power-bandwidth-gain product reaches record high in the designed spectral range. We envisage that this new developed terahertz TWT will have broad application prospects, such as in long-range radar and communication systems.

This article reports a slow-wave structure (SWS) working at 1 THz which can be fabricated through nano-computer numerical control (nano-CNC) technology for the first time. First, a 1 THz deformed quasi sine waveguide (D-QSWG) SWS has been designed and simulated in this article. To reduce the metal loss of input and output waveguide, a coupler which transit the waveguide to over mode rectangular waveguide has been designed. The simulation result shows that input and output waveguides with this coupler have lower metal loss than that of WR1 rectangular waveguide. To fabricate the designed D-QSWG SWS, tungsten steel endmills have been used. The fabricated SWS has the surface roughness around 58–74 nm, the corresponding effective conductivity is around $2\times 10^{{7}}$ –1.85 $\times 10^{{7}}$ S/m. And the cold test results show that the insertion loss of the fabricated model is less than 30 dB while the reflection loss is less than −15 dB in the frequency range of 0.998–1.016 THz, which has a good consistency with the simulated results. The beam-wave interaction simulation results based on the cold test results show that the designed D-QSWG traveling wave tube (TWT) has the output power of 300 mW, and the 3 dB bandwidth is around 3 GHz.

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 ^* 0.148 mm and 0.025 mm ^* 0.114 mm, respectively, will lead to a very high beam current density (906.9 A/cm ² ). 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.

For the efficient optimization of a multistage depressed collector (MDC), an axis-adjustable MDC optimized using the genetic algorithm (GA) is presented in this article. The optimization processes are realized with a reasonable balance between the collector recovery efficiency and electron reflux rate by modifying the fitness function of GA. Through the proposed method, the best recovery efficiency 88.5% and 0.72% electron reflux rate of MDC are obtained, and a three-stage symmetric collector has been designed with the GA optimization and fabricated, for a 0.22-THz TWT. The experimental results are in well agreement with that of simulations, which indicates that the methods we propose would be beneficial to the design of high efficiency of TWT.

An extended interaction klystron (EIK) working at the frequency of 340 GHz is designed in this present article. The characteristic impedance, coupling coefficient, and normalized electron conductance of the cold cavities are analyzed and optimized. To improve the output power, the EIK adopts a prebunching (PB)-cavity high-frequency structure (HFS). Compared with the conventional terahertz (THz) EIK, the coherence of PB-cavity EIK is enhanced, and the output power is improved. The 3-D particle-in-cell (PIC) simulation predicts the EIK, driven by a 0.20-A, 22.4-kV electron beam confined in a 0.2-mm-diameter beam tunnel, and generates an output power of 138.3 W at the frequency of 339.7 GHz. The gain, electronic efficiency, and 3-dB bandwidth are 39.6 dB, 3.1%, and 500 MHz, respectively. The proposed EIK can be applied to the THz high-resolution radar.