Carbon nanotube (CNT) cold cathodes are proving to be compelling candidates for miniaturized terahertz (THz) vacuum electronic devices (VEDs) owning to their superior field-emission (FE) characteristics. Here, we report on the development of a multi-sheet beam CNT cold cathode electron optical system with concurrently high beam current and high current density. The microscopic FE characteristics of the CNT film emitter is captured through the development of an empirically derived macroscopic simulation model which is used to provide representative emission performance. Through parametrically optimized macroscale simulations, a five-sheet-beam triode electron gun has been designed, and has been shown to emit up to 95 mA at 3.2 kV. Through careful engineering of the electron gun geometric parameters, a low-voltage compact THz radiation source operating in high-order TM 5 , 1 mode is investigated to improve output power and suppress mode competition. Particle in cell (PIC) simulations show the average output power is 33 W at 0.1 THz, and the beam–wave interaction efficiency is approximately 10%.

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A disk-loaded coupled cavity structure operating in the quasi-TM03 mode has been used here to develop a high electron efficiency, high output power terahertz radiation source, demonstrating that it is possible to concentrate the axial field energy along the source’s central axis within a large cavity. Compared with traditional extended interaction devices operating at the same frequency band, the operating mode of this present device provides a sizable beam tunnel capacity that can support efficient energy conversion between the electron beam and the high frequency field. The developed electron optical system is based on a cylindrical electron beam of 0.3 mm radius and is capable of producing a beam current of 0.65 A at a bias of 16.4 kV. Particle in cell simulations show that such new design approaches can achieve kilowatt-level output power at 0.22 THz with a high electron efficiency of 11.5%.

In this paper, we investigate a large-sized beam tunnel, G-band extended interaction klystron (EIK) with a traveling wave output structure for the development of broad bandwidth EIKs. The high-quality factor F was introduced to estimate the bandwidth characteristics of the cluster cavities, and the optimal cluster cavity structure parameters were obtained based on this factor. The simulation mode of the device was designed by the 3D particle-in-cell (PIC) commercial simulation software. Four cluster cavities with a staggered distribution of frequencies were employed to expand the bunching bandwidth, and two traveling wave modes, 2π−π/10 and 2π−2π/10, were used as the operating modes in the output structure, effectively increasing the output bandwidth. The simulation findings show that the maximum output power is 170 W, the corresponding gain is 37.5 dB, and the 3-dB bandwidth is up to 1.25 GHz. The three-hole coupling structure with a large-sized beam tunnel provides convenience for the fabrication of devices in the G-band, and our study shows a potential method for the realization of a G-band broadband EIK.