Liangjie Bi

The effect of velocity spread of pseudospark-sourced electron beam to Y-band extended interaction oscillator

Extended interaction oscillator (EIO) operation in the terahertz range puts greater demand on the current density and brightness of an electron beam. The pseudospark (PS)-sourced electron beam is a good candidate for driving such high frequency EIOs as it has a very high combined beam current density and brightness. However, the PS-sourced electron beam can have an inherent velocity spread unless some form of post acceleration is used. Before a new EIO device in the Y-band (220 GHz–325 GHz) based on a PS-sourced electron beam can be realized, it is first necessary to analyze the influence of the beam velocity spread on performance. This paper presents the numerical studies of the EIO performance with the inclusion of the beam velocity spread. It was found that the Y-band EIO circuit can operate in a relatively wide velocity spread range when a high beam current density is used. For an electron beam current density of 1 kA/cm2, the output power is not less than 0.9 times of the power obtained with an elect...

A Novel Wire-Wrap Slow-Wave Structure for Terahertz Backward Wave Oscillator Applications

An innovative wire-wrap structure was applied as the slow-wave circuit for a backward wave oscillator (BWO) operating in terahertz (THz) band. The construction of the device features a periodic fine copper wire, a rectangular ridged waveguide, and a rectangular cavity in the upper cover plate. Based on the novel structure, the performance of the device presented by dispersion characteristic, coupling impedance, and S-parameters was analyzed and optimized in the design process. The electron beam parameters with an outer diameter of 0.26 mm have relatively low accelerating voltage around 1.2 kV and beam current of 0.05 A (the current density is 94 A/cm2). Under such conditions, numerical simulation results predict that the novel oscillator is capable of achieving the output peak power in excess of 154 mW and a tunable 3-dB bandwidth over 24 GHz in the range from 324 to 348 GHz. In addition, the machining and assembling methods of wire-wrap structure are another original invention for the physical processing of THz BWO.

Design and analysis of a W-band high power extended interaction oscillator with distributed hollow electron beam

The circuit suitable for the hollow electron beam (HEB) interaction was formed by parallel connecting of the sheet beam extended interaction klystron circuit at the angular direction. The analysis of this newly developed circuit shows it can interacts with the distributed HEB. To demonstrate this capability, a W-band extended interaction oscillator (EIO) with distributed HEB has been designed. A DC distributed HEB with 27 keV energy and 8A current was injected into the interaction circuit, simulations with a 3-D Particle-in-cell (PIC) code predict an output power up to 6.6 kW at 99.7 GHz was obtained.

Circuit design of a three-cavity W-band extended interaction klystron

A compact three-cavity circuit with ladder type structure is designed for the pencil beam W-band extended interaction klystron (EIK). Circuit parameters such as coupling coefficient M, characteristic impedance R/Q and beam-loading conductance Ge are analyzed and optimized in the design procedure. The initial beam parameters are 18.1 kV, 0.2 A and 0.5 mm in diameter. Simulation predicts a saturation output power of 300 W is achieved at 94.5 GHz with an input power of 290 mW, corresponding to the gain of 30 dB and electronic efficiency of 8.3%.

Preliminary study of the mode-hopping phenomenon in extended interaction oscillator

The mode-hopping phenomenon in extended interaction oscillator (EIO) based on the multiple-gap topology resonant system is studied to verify the remarkable advantage of the electronic tuning property for EIO. In contrast to the conventional EIO where electron beam interacts with the standing-wave mode in a narrow operating voltage range, the presented EIO can operate in a sequence of neighboring backward-wave modes by switching the beam voltage. According to particle-in-cell (PIC) simulation in CST, the mode-hopping effect has resulted in radiation power fluctuation. Simulation results demonstrate that the EIO is capable of electronic tuning in a relatively wide operating voltage range from 4.1 kV to 9.5 kV. An output power on the order of a few tens of watts is obtained. The study of the mode-hopping effect can show a promising way to operate the EIO in the backward-wave regime.

Start current study of a THz sheet beam extended interaction oscillator

This paper presents a theoretical study on a start current of a 0.378 THz sheet beam extended interaction oscillator (SB-EIO), and the design of this device driven by thermionic cathode stands a chance to realize a compact and powerful THz coherent continuous radiation sources. After theoretical study, the SB-EIO with eleven gaps is designed to operate at 2π mode. The coupling and interaction abilities are optimized to meet the synchronization conditions and thus improve the output power and efficiency. The start current analysis is preliminarily accomplished, and the advantages are: (1) At the operation frequency of 0.378 THz, the start current and current density of the device are optimized to 20 A/cm2 and 8.4 mA, and the output power is 14 W. (2) It works in the condition of smooth copper plane in simulation, and the output power is still about 20 W when an electron beam with 252 mA and 41 kV is injected. The research gives an estimation of up to 3.5 times decline in output power when the surface roughness emerges. (3) The results of the simulation show that a relatively high efficiency of ∼13% in particle-in-cell (PIC) was observed, and a stable output power range from 98 W to 234 W is found when the injected electron beam (0.35 mm × 0.12 mm) is 16.8–42 mA and 42 kV. Moreover, the reliability of PIC results is verified in this paper.This paper presents a theoretical study on a start current of a 0.378 THz sheet beam extended interaction oscillator (SB-EIO), and the design of this device driven by thermionic cathode stands a chance to realize a compact and powerful THz coherent continuous radiation sources. After theoretical study, the SB-EIO with eleven gaps is designed to operate at 2π mode. The coupling and interaction abilities are optimized to meet the synchronization conditions and thus improve the output power and efficiency. The start current analysis is preliminarily accomplished, and the advantages are: (1) At the operation frequency of 0.378 THz, the start current and current density of the device are optimized to 20 A/cm2 and 8.4 mA, and the output power is 14 W. (2) It works in the condition of smooth copper plane in simulation, and the output power is still about 20 W when an electron beam with 252 mA and 41 kV is injected. The research gives an estimation of up to 3.5 times decline in output power when the surface rough...

Study of Electronic Switching Between Multiple Backward-Wave Modes in a W-Band Extended Interaction Oscillator

The performance of electronic switching between multiple backward-wave modes is studied in a designed extended interaction oscillator (EIO) based on a ladder circuit with finite number of periods to overcome electronic tuning range limits of EIOs operated in standing-wave mode. The dispersion characteristic of the circuit with finite number of periods, which is constructed by a series of discrete modes, is investigated. The mode separation is analyzed and reduced to support continuous switching between multiple different modes by increasing the number of periods as compared with the standing-wave EIO approach. An output circuit is designed to extract the power of backward wave. The electronic switching between nine backward-wave modes has been achieved by changing the beam voltage from 4.1 to 10.5 kV, where the maximum output power over 58 W is obtained at 5.3 kV from the simulation prediction. The EIO can operate over an electronic tuning range of 3.53 GHz from 89.65 to 93.18 GHz in ensuring the output power no less than 20 W. This technique can be extensively applied to increase operating band for extended interaction klystrons (EIKs) and electronic tuning range for EIOs, making them more suitable for many potential applications.

Preliminary design of a THz EIO based on the pseudospark-sourced sheet electron beam

Extended interaction oscillator (EIO) operated in the terahertz range puts greater demand on current density and brightness of electron beam. The pseudospark-sourced (PS) electron beam is an attractive candidate to drive such high frequency EIOs. The study of a THz EIO driven by a PS sheet electron beam is presented. This enables the advantages of a interaction circuit combined with the merits of a PS sheet electron beam, including large beam cross section, high current density and the fact that a PS electron beam does not require the use of an external focusing magnetic field. This paper presents the latest results that demonstrate the design and optimization of THz EIO driven by a 210 mA (500 A/cm2) PS-sourced electron beam. A peak power over 0.78 kW at 0.388 THz was achieved using a pseudospark-sourced sheet electron beam.

Design of a Ka band multiple-beam gun

A study for designing a multi-purpose, miniature, multiple-beam electron optical system is presented in this paper. A matched magnetic circuit was also designed. We used pierce method to design the gun, 3D simulation software to optimize the optical system and magnetic circuit. A three-beam pierce electron optical system was designed to produce a total current of 3×0.87A divided equally among the three beams at an accelerating potential of 15kV, and the radius of beam tunnel is 1mm. It also consists of solenoid magnet structures to optimize the beam radius, which produce 0.52T magnetic field. This gun have vast prospect, which can be used for vacuum electronic devices, photonic crystals gyrotron and artificial electromagnetic new type medium.