Xianfeng Tang

Study on Wideband Sheet Beam Traveling Wave Tube Based on Staggered Double Vane Slow Wave Structure

In this paper, a wideband 220-GHz sheet-beam traveling-wave tube (TWT) based on staggered double vane slow-wave structure (SWS) is investigated. A novel method of loading the attenuator into the SWS for suppressing backward wave oscillation is proposed. In addition, a novel focusing electrode of the sheet beam gun is carried out in this paper, which is a whole structure but divided into two parts artificially, one is used to compress the electron beam in X-direction and the other is used to compress the electron beam in Y-direction. In addition, a novel anode is redesigned to reduce the defocusing effect caused by the equipotential surfaces. A nonuniform periodically cusped magnet is used for focusing the sheet electron beam, which is predicted to exhibit 100% beam transmission efficiency in a 75-mm length drift tube. The high-frequency characteristics of the SWS and the beam-wave interaction are also studied. The results reveal that the designed TWT is expected to generate over 78.125-W average power at 214 GHz, and the 3-dB bandwidth is 31.5 GHz, ranging from 203 to 234.5 GHz.

All-metal metamaterial slow-wave structure for high-power sources with high efficiency

In this paper, we have proposed a metamaterial (MTM) which is suitable for the compact high-power vacuum electron devices. For example, an S-band slow-wave structure (SWS) based on the all-metal MTMs has been studied by both simulation and experiment. The results show that this MTM SWS is very helpful to miniaturize the high-power vacuum electron devices and largely improve the output power and the electronic efficiency. The simulation model of an S-band MTM backward wave oscillator (BWO) is built, and the particle-in-cell simulated results are presented here: a 2.454 GHz signal is generated and its peak output power is 4.0 MW with a higher electronic efficiency of 31.5% relative to the conventional BWOs.

Observation of the reversed Cherenkov radiation.

Reversed Cherenkov radiation is the exotic electromagnetic radiation that is emitted in the opposite direction of moving charged particles in a left-handed material. Reversed Cherenkov radiation has not previously been observed, mainly due to the absence of both suitable all-metal left-handed materials for beam transport and suitable couplers for extracting the reversed Cherenkov radiation signal. In this paper, we develop an all-metal metamaterial, consisting of a square waveguide loaded with complementary electric split ring resonators. We demonstrate that this metamaterial exhibits a left-handed behaviour, and we directly observe the Cherenkov radiation emitted predominantly near the opposite direction to the movement of a single sheet electron beam bunch in the experiment. These observations confirm the reversed behaviour of Cherenkov radiation. The reversed Cherenkov radiation has many possible applications, such as novel vacuum electronic devices, particle detectors, accelerators and new types of plasmonic couplers.

Study on two kinds of novel 220 GHz folded-waveguide traveling-wave tube

Two kinds of novel 220 GHz folded-waveguide (FWG) slow-wave structure (SWS) with different electron-beam tunnels are presented for producing a high power and considerable bandwidth. These structures, which have the potential to have a better performance than the conventional FWG SWS, are suitable for circle-beam electron guns and sheet-beam electron guns, respectively. In this study, the electromagnetic characteristics and nonlinear interaction between the electron beam and the electromagnetic field of the two kinds of novel FWG are investigated on the basis of simulation results. The influence of the beam tunnel with respect to its transverse shape and size on the circuit performance is investigated in detail. With different beam tunnels, the two novel FWGs exhibit similar radio-frequency characteristics and signal gain. Particle-in-cell simulation results reveal that the novel tubes exhibit a gain greater than 32 dB and a bandwidth of 10% with a 16.5 kV and 150 mA electron beam and a 90 mW peak input power. Compared with the conventional FWG SWS, the novel FWGs have 32% higher output power under optimized conditions.

Theoretical and Experimental Research on a Novel Small Tunable PCM System in Staggered Double Vane TWT

In this paper, a novel small tunable periodic cusped magnet (NSTPCM) system is proposed for the purpose of realizing low voltage, big current sheet electron beam propagation in a long distance in engineering, which is composed of a series of position-fixed magnet blocks in alignment and freely sliding staggered pole pieces. This kind of NSTPCM not only generates higher magnetic field in the axial direction but also realizes more convenient adjustment of magnetic field in the transverse direction. This NSTPCM system has been successfully applied in a Ka-band sheet electron beam staggered double vane traveling wave tube. The tested sheet beam transmission efficiency is >93 % in a 112.7-mm-length slow-wave structure under the condition of beam voltage 24.3 kV and beam current 0.8 A. Moreover, the measured output power is >75 W in the range from 33 to 37.5 GHz, and the maximum output power is 128 W at 34 GHz. This paper provides the foundation for the development of sheet electron beam vacuum devices.

Sheet Electron Beam Transport in a Metamaterial-Loaded Waveguide Under the Uniform Magnetic Focusing

We have theoretically investigated the transport of a sheet electron beam focused by a uniform axial magnetic field in a metamaterial-loaded waveguide. A theoretical model has been proposed to analyze the sheet electron beam transport. In this model, we have used CST simulations to obtain the mean potential on the metamaterial as the boundary condition. According to the boundary condition, the space-charge electric field and the beam curling have been theoretically analyzed. It is found that the beam curling can be greatly reduced by decreasing the spacing between the metamaterial and the sheet electron beam. This model is verified using the CST simulations. This paper can pave the way for developing brand new metamaterial-based vacuum electron devices with a sheet electron beam.

Design of the radial divergent sheet beam electron optical system with radial quasi-uniform magnetic field

The radial divergent sheet beam electron optical system focused by a radial uniform magnetic field is designed in this paper. It is shown that the radial divergent sheet beam with size of 8 deg×0.23 mm, generated by the electron gun with 1700V, 151 mA, can stably pass through the beam drift tunnel with transverse size of 20 deg×0.52 mm and the length of 20 mm in a radial quasi-uniform magnetic field.

Sheet electron beam formation and transport in the uniform magnetic field

In this paper, we have presented the simulation results on sheet beam electron gun and sheet beam transport in a uniform magnetic field. It is shown that the sheet beam with size 4.6 mm×0.4 mm, generated by the electron gun with 20 kV, 560 mA, can stably pass through the beam tunnel with transverse size 6 mm×1 mm and the length 120 mm in a uniform magnetic field.

Metamaterial-based high-power microwave radiation sources

We propose a metamaterial slow-wave structure (SWS) which is composed of a circular waveguide periodically loaded with complementary electric split ring resonators (CeSRRs). The high-frequency characteristics of the metamaterial SWS have been studied, and the simulation results reveal that it is a kind of SWS of higher interaction impedance. An S-band metamaterial microwave radiation source is calculated by particle-in-cell (PIC) simulation, the results show that it is a potential high-power microwave radiation source.

Novel vacuum electronic devices based on reversed cherenkov radiation

In this paper, we present a square waveguide loaded by planar complementary electric split ring resonators (CeSRRs), which is considered as a novel slowwave structure (SWS). The transmission characteristics of the novel SWS are studied by simulation. The results indicate that the novel SWS have good transmission characteristics at the operating frequencies. On this basis, the beam-wave interaction is studied by particle-in-cell (PIC) simulations to verify the reversed Cherenkov radiation (RCR). The results show that the novel SWS interacting with the sheet beam can generate output power of ~ 4 MW at the beam entrance. The proposed novel SWS can be developed into novel vacuum devices.