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This paper reports our progress of developing a 0.33-THz gyrotron which is based on a compact pulse magnet and can generate broadband coherent THz radiation with bandwidth exceeding 10 GHz and peak power about 2 kW. The design and fabrication of the key components are addressed in detail, including strong-field magnet, pre-bunched cavity, broadband Quasi-Optical mode converter, and Brewster window...
Spoof surface plasmons (SSP) is the localized collective electron oscillation mode which is propagating along the corrugated metal surface. The extreme strong near field of SSP mode is very attractive to develop novel terahertz (THz) electronic source. In this paper, SSP-assisted enhanced Terahertz vacuum electronic sources on the metallic grating have been studied with the help of particle-in-cell...
This paper presents a broadband quasi-optical (QO) mode converter antenna system, which can transfer a waveguide TE62 mode into free-space Gaussian beam around 330 GHz. The converter contains a Vlasov launcher and three reflector mirrors. Special considerations, including a reasonably large aperture of the Vlasov launcher and the optimized combination of two elliptic reflectors and a bifocal parabolic...
Cylindrical waveguide loaded with metadielectric structure is investigated to convert symmetric model into higher-order cylindrical waveguide mode. With the angular periodic dielectric grating coated with dielectric in the cylindrical waveguide, the TE04 mode can be converted to a ultra-high-order TE20,15 mode. Simulation results presented here verify the feasibility of such high-order mode converter...
The extreme strong near field of spoof surface plasmon (SSP) on the corrugated metal surface is attractive to develop powerful and efficient Terahertz (THz) electronic sources. In this paper, a THz electronic source based on the generation of SSP modes on the asymmetric doubly-corrugated waveguide is studied both theoretically and numerically. Dispersion characteristics of SSP modes on the asymmetric...
Modes in cylindrical waveguides with periodic subwavelength metal grating loaded on the inner surface are analyzed by both theory and simulation. Coupling between spoof surface plasmon mode and traditional waveguide mode provides a robust way to build TM02 single mode operation. Furthermore, a new approach to realize the well-integrated and reciprocal mode conversion between TM01 mode and TM02 mode...
In this paper, a novel terahertz electronic sources based on the interaction between spoof surface plasmons (SSP) and injected electron beam on the doubly-corrugated metasurfaces are studied by particle-in-cell (PIC) simulation. The SSP fields, dispersion and modes on the two identical corrugated surfaces are calculated and then presented theoretically and numerically. Besides, the influence of the...
The gyrotron is capable of efficiently generating high-power millimeter-terahertz radiation. In THz waveband, the bulky volume is one of the major factors hindering the gyrotron development. It is in pressing demand for the mini-table-top gyrotrons. In order to reduce the volume of the cathode, a broadband ultra-low-voltage gyrotron is investigated in this paper. Through parameter optimization, the...
A new hyperbolic gradient-index metalens is demonstrated at terahertz (THz) frequency, which can realize enhanced Fourier transform with extended spatial frequency bandwidth. The bandwidth can be extended to 2.5k0 (k0 is the wave-vector in air), which is 2 to 3 times of conventional lens. Furthermore, the working distance can be larger than one wavelength, and the input and output surfaces are flat,...
In this paper, a low-voltage high-efficiency 330 GHz tunable gyrotron is investigated, which operates on the open-cavity TE6,2 mode and employs an electron beam with voltage of 20 kV, current of 0.5A, and pitch factor of 1.5. Simulation achieves a competitive efficiency, more than 40%, under the assumption of using copper circuit wall and electron beam of 5% velocity spread. Besides, the investigation...
This paper presents the recent development of a 0.33 THz pulse gyrotron, operating on the fundamental harmonic co-rotating TE62+(1) mode. It employs a novel pre-bunched interaction circuit. The pulse magnet generates a time varying magnetic field to tune the radiation frequency via backward wave interaction. The optimized system is capable of generating radiation power about 1 kW ∼ 2 kW during 330...
This paper presents the design of a broadband quasi-optical mode converter for a 330 GHz TE62 mode tunable gyrotron. It consists of a Vlasov launcher and three reflector mirrors. A series of important considerations, including Vlasov launcher of reasonable radius, robust and simple system configuration, are the keys to realize stable and broadband mode converting. The optimized internal converter...
Spoof surface plasmon polaritons (SSPPs), as a new frontier in the terahertz (THz) range, is difficult to be effectively directional launched. In this paper, based on the near-field interference of the SSPPs generated by a pair of slits, we demonstrate that the oblique incident plane wave results in the unidirectional excitation of SSPPs. The extinction ration obtained with the finite element method...
This abstract presents a complete study of dispersion and mode distribution of spoof surface plasmons (SSPs) in planar metal gratings. The subject under investigation is intended for Terahertz wave generation. Because of its characteristics of near field localization of this plasmonic wave and collective resonance effects of electrons in metals, SSPs in this textured metal surface has attracted enormous...
A 0.33THz pulse gyrotron is currently under development at Peking University, which is predicted to generate coherent broadband radiation in each pulse. The pulse gyrotron is designed based on the fundamental harmonic co-rotating TE62+(1) mode. The scheme of tuning magnetic field on backward-wave interaction is adopted to realize broadband radiation. The compact pulse gyrotron is promising in the...
The nonlinear analysis of a 330 GHz second-harmonic TE94 mode low-voltage gyrotron is presented in this paper. With electron beam of voltage 20 kV and current 0.5 A, the interaction circuit is optimized to achieve efficiency up to 13.6%. Based on nonlinear analysis, mode competition of the gyrotron is preliminarily revealed. The gyrotron is promising to be applied in 500MHz dynamic nuclear polarization...
A 1 THz vacuum electronic source has been designed and implemented by Particle-in-cell (PIC) simulation based on rectangular grating slow-wave structure (SWS) and half duty cycle electron beam. The dispersion relation and coupling impedance are analyzed numerically. The simulation results predict that this designed 1 THz vacuum source can produce maximum 102 W saturated power at the end of structure...
In this paper, the simulation and design of a diode type magnetron injection gun (MIG) for a W-band CW gyrotron oscillator is presented. The simulation of the MIG, operating at the voltage of 55kV and the current of 4A, is finished with the help of a trajectory program EGUN. The simulation results indicate that the velocity ratio with velocity spread of less than 2.5% is 1.43.
In this paper, the design of a magnetron injection gun (MIG) with a single-anode built for W-band gyrotron oscillator is presented. The simulation of the MIG is finished with the help of a trajectory program EGUN. The simulation results indicate that the velocity ratio with velocity spread of less than 4% is 1.41.
In this paper, the analysis of a conventional W-band gyrotron oscillator operating with TE02 mode has been investigated through the particle-in-cell (PIC) simulation. The influence of the variations of the operating parameters (such as beam voltage, beam current, velocity ratio) on the output power and electron efficiency has been studied in detail. The PIC simulation predicts 33.4kW output power...
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