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.

To improve the performance of efficiency bandwidth product (EBP) and power capacity for G-band continuous-wave traveling-wave tube (CW TWT), a novel staggered U-shaped groove sine waveguide slow-wave structure (SUGSWG SWS) is proposed in this article. The theoretical analysis of high-frequency and beam–wave interaction characteristics indicates that the SUGSWG TWT has low insertion/reflection loss, broadband (3-dB power bandwidth of over 19 GHz), and high maximum output power (over 66 W), of which the EBP could reach whopping 103% $\cdot$ GHz (about three times the state of art). In the merit of its special geometry, the power capacity of this novel SWS is also about 1.6 times its existing peers. A prototype of a two-section SUGSWG TWT is designed, fabricated, and experimented for verifications. The hot test demonstrated that the peak power of 56 W, the 3-dB power bandwidth of 16 GHz, and the EBP of 75.4% $\cdot$ GHz were achieved, with the transmission rate practically tuned around 93%. Those measurement results are consistent with the theoretical predictions under the same transmission conditions. Those studies validate the remarkable potential of our proposed novel slow wave structure (SWS) in TWTs for THz applications.

The transport of sheet electron beam (SEB) is of critical importance for the success of a number of high-power millimeter wave and terahertz vacuum devices. In this paper, the condition to achieve the SEB's stable transport in uniform longitudinal magnetic field is studied. Based on this stability condition, a new approach, named sheet electron beam matching focusing magnetic (SEB-MFM) field, which consists of a longitudinal component and a tiny transverse component, is presented. The SEB-MFM field can be generated by adding extra transversely magnetized magnets to the conventional uniform magnetic (UM) system. For demonstrating the effect of the SEB-MFM field, the simulation work of the SEB-MFM field and conventional UM field is carried out for an electron optical system employing a SEB. The simulation results show that the SEB-MFM field effectively eliminates the instabilities, such as distortion and deformation, arising from the longitudinal magnetic field. In addition, comparing with conventional UM field, the SEB-MFM can achieve the stable and long-distance transport of a SEB with a pretty low magnetic field strength. Finally, a new magnetic system generating SEB-MFM field is designed, fabricated, and measured.

A phase shift that is caused by the machining errors of independent circuits would greatly affect the efficiency of the power combination in traditional multi-beam structures. In this paper, to reduce the influence of the phase shift and improve the output power, a multi-beam shunted coupling sine waveguide slow wave structure (MBSC-SWG-SWS) has been proposed, and a multi-beam overmoded flat-roofed SWG traveling wave tube (TWT) based on the MBSC-SWG-SWS was designed and analyzed. A TE₁₀-TE₃₀ mode convertor was designed as the input/output coupler in this TWT. The results of the 3D particle-in-cell (PIC) simulation with CST software show that more than a 50 W output power can be produced at 342 GHz, and the 3 dB bandwidth is about 13 GHz. Furthermore, the comparison between the single-beam sine waveguide (SWG) TWT and the multi-beam overmoded SWG TWT indicates that the saturated output power of the multi-beam overmoded SWG TWT is three times more than that of the single beam SWG TWT.

Folded waveguide (FWG) traveling wave tube (TWT) is an attractive choice for a high-power amplifier. This article proposes a novel slow wave structure (SWS) called sine-shaped FWG (S-FWG), which is derived from conventional FWG. With the feature of transforming the arc-shaped segment of the traditional FWG into the sinusoidal waveguide, the proposed structure could be quickly optimized by modifying the amplitude of the two sine curves, and it has an ability to produce a greater interaction impedance compared to the traditional FWG SWS with the same frequency band, which, under the same operating conditions, is expected to result in a higher output power. Using CST Microwave Studio, the high-frequency properties and beam–wave interaction were simulated. Simulation results indicate that the S-FWG TWT reaches a maximum output power of 16.82 W and a gain of 32.25 dB at 330 GHz with an operating voltage of 19.4 kV, a beam current of 30 mA, and an input power of 10 mW. The S-FWG SWS should therefore be regarded as a promising SWS for the high-power terahertz (THz) traveling wave amplifier.

The multibeam klystron (MBK) faces the challenge of miniaturization together with stringent requirements for high power and high efficiency (HE) in L -band and below frequency regimes. Inspired by the core stabilization method (CSM), this article proposes three types of hybrid-modes resonant cavities, which can operate simultaneously in two harmonic modes. The large-signal simulation and 3-D particle-in-cell (PIC) simulation results demonstrate that this novel CSM MBK equipped with two hybrid-modes resonant cavities, operating at both fundamental and second harmonics, could provide up to 11.5-MW output power with 65.9% electronic efficiency at a total circuit length of 592 mm. This L -band MBK is launched with six beamlets, of which the beam voltage is 110 kV and the total current is 168 A. Moreover, compared with the MBKs designed by the traditional approach with only fundamental cavities or the CSM approach with individual harmonic cavities, the new hybrid HE klystron proposal exhibits not only decent efficiency performance but also, more importantly, ultracompact dimensions, where the circuit length is significantly shortened by about 45% and 35%, respectively.