Beam-wave Interaction Simulation Research Articles

Dual frequency gyrotron operating at 42/84 GHz for plasma fusion application

The design study of dual frequency gyrotron operating at 42/84 GHz frequencies with output power ∼500 kW is presented in this article. TE10,4 and TE6,2 are selected as the operating modes for 84 and 42 GHz operations of the device, respectively. The beam-wave interaction simulations are performed by using the Particle-in-Cell algorithm to evaluate the growth of RF power and frequency. Magnetically tunable magnetron injection gun is also designed to launch the electron beam at the radius of 6.2 mm (84 GHz) and 7.3 mm (42 GHz) in the interaction cavity. The CVD diamond RF window is also designed, which must be transparent for 42 GHz and 84 GHz frequencies. The design results of the dual frequency gyrotron confirm the growth of ∼500 kW power at 42/84 GHz.

Research on the 650GHz Folded Waveguide BWO

The terahertz (THz) spectrum technique has become an important research content of electromagnetic field in recent years. Folded waveguide backward wave oscillator (BWO) is suitable to be used as THz high-power electromagnetic radiation source. Because it can realize electronic tuning within a wide frequency band and doesn’t require pre-stage source amplifier. In this paper, the high frequency characteristic, the transmission characteristics, and the particle beam wave interaction characteristics of the structure of folded waveguide BWO have been analyzed, and it is utilized to design geometry parameters of 650GHz folded waveguide slow-wave-structure (SWS). The design is been validated by particle beam wave interaction simulation experiments. The experiment results show that the output is over 1.7W within 42GHz bandwidth, and the electron efficiency can exceed 1%.

Numerical study and simulation of a 170 GHz megawatt-level corrugated coaxial-gyrotron

As the sources of high-power microwave and terahertz, gyrotrons have important development prospects. However, there are many difficulties to be resolved in study and design of gyrotrons meeting requirements. In this paper, the beam-wave interactions of a 170 GHz megawatt-level corrugated coaxial-gyrotron are studied numerically. In order to attain high efficiency and stable radiation, TE31,12 mode that lies in a relative sparse spectrum is selected as the operating mode and the beam-wave coupling coefficient, and start oscillation current are calculated by a set of source codes. Taking into account electronic velocity spread, and cavity wall resistivity and basing on single-mode approximation, the optimized design and simulation of beam-wave interaction of a 170 GHz MW corrugated coaxial-gyrotron have be fulfilled. The relationships between the efficiency and magnetic field, voltage, current, and parameters of groove are presented. The results show that voltage and magnetic field have great influences on efficiency, but the current and velocity spread do slightly, so reduce the requirements of electronic gun design. In addition, the optimized geometry parameters can improve efficiency, reduce the impact of velocity spread on efficiency, and achieve around 48.6% electronic efficiency and 1.7 MW output power at 5% velocity spread, and 6.896 × 10−8 Ω m resistivity.

Recent Developments to the Microwave Tube Simulator Suite

Recent developments to microwave tube simulator suite (MTSS) are reported in this paper. The MTSS is a full-featured tightly integrated software package for microwave tube analysis and design. It includes a commercial grade user interface and three physics simulators. The electron optics simulator is a finite-element (FE) 2-D and 3-D electrostatic steady-state beam trajectory code that has been used to design beam optics, including electron gun and collector. High-frequency circuit simulator is a full 3-D FE computational electromagnetic code that aims to get the accurate electromagnetic wave character spreading in high-frequency structures, such as dispersion, coupling impedance, and attenuation. Beam wave interaction simulator is a large-signal simulation code for helix traveling wave tubes (TWTs), coupled-cavity TWTs, and klystrons. The first version of MTSS was released in 2007, and all of these three physics simulators and user interface are improved and updated over the past six years. This paper reports on some significant advances to MTSS; new Ribbon style user interface, a lot of component modeling templates, more abundant postprocessing features, parallel version, full 64-bit version, more physics, and computation methods improvement.

Design of slow-wave structure and beam-wave interaction simulation for helix traveling-wave tube

A Ku-band helix traveling-wave tube (TWT) is designed using theoretical analysis and simulation. The effect of the variation in inner radius on dispersion and coupled impedance is analyzed to optimize the slow-wave structure of helix TWT. The input and output structure of TWT is simulated, the input reflecting coefficient is less than -19 dB and the voltage standing wave ratio (VSWR) is less than 1.24. Periodic permanent-magnetic field is used as electromagnetic focusing system, the magnetic system period is 8.5 mm and the magnetic peak value is 0.17 T. The slow-wave circuit with property of dynamic velocity tapper (DVT) is used to increase the interaction efficiency, it can provide enough time for the interaction of beam and high-frequency field and make electrons continuously transport energy to high-frequency field. The helix TWT is simulated using a three-dimensional particle-in-cell (PIC) code. The simulation results demonstrate that the output power is bigger than 88.7 W, the electron efficiency is bigger than 14.8% and the saturated gain is bigger than 34.6 dB in the frequency range from 12.5 to 16.0 GHz.

RF behavior of triple-frequency high power fusion gyrotron

The RF behavior of high power, triple frequency (170-, 127.5-, and 85GHz) gyrotron for fusion application is presented in this paper. The operating mode selection is discussed in detail for each corresponding frequencies and TE34,10, TE25,8 and TE17,5 modes are selected as the operating mode for 170GHz, 127.5GHz and 85GHz operation of the device, respectively. The interaction cavity geometry and beam parameters are finalized by the cold cavity analysis and beam-wave interaction simulations. Considering the beam parameters and the beam launching positions in cavity (beam radius), the design of Magnetically Tunable MIG (MT-MIG) is also presented. Results of MT-MIG confirm the beam launching with desired beam parameters at the beam radius corresponding to the selected operating modes for all three frequencies. The CVD diamond window is also designed for RF power transmission. The beam-wave interaction simulations confirm more than 1MW power at all three frequencies (170-, 127.5-, and 85GHz).

Analysis and calculation of a 170 GHz megawatt-level coaxial gyrotron

Gyrotrons are the most promising microwave source devices that can be used in the International Thermonuclear Experimental Reactor, but there are many difficulties to be solved in study and design of gyrotrons to meet the requirements. In this paper, the beam-wave interactions of a 170 GHz megawatt-level smooth-wall coaxial gyrotron are studied numerically. In order to attain high efficiency and stable radiation, TE31,12 mode that lies in a relative sparse spectrum is selected as the operating mode, and the beam-wave coupling coefficient and start oscillation current are calculated by a set of source codes developed by Matlab. Taking into account the electronic velocity spread and cavity wall resistivity, and based on a single-mode approximation, the optimization design and simulation of beam-wave interaction of a 170 GHz megawatt smooth-wall coaxial gyrotron have been fulfilled. The relationships between efficiency and magnetic field, and the voltage, current, taper angle of insert, and other parameters are presented. Results show that the voltage and magnetic field have great influence on efficiency; however, the current and velocity spread do change slightly, thus reduce the requirements of electron gun design. In addition, the optimized taper angle of insert and coaxial cavity geometry parameters can improve the efficiency, reduce the impact of velocity spread on efficiency, and can achieve an electronic efficiency around 50% and an output power 1.7 MW.

螺旋线行波管慢波结构设计及注波互作用模拟

螺旋线行波管慢波结构设计及注波互作用模拟

Design of interaction cavity of a 170-GHz, 1-MW gyrotron for ECRH application

The design of the interaction cavity of a 170 GHz gyrotron operating in the TE 34,10 mode is presented in this article. An in-house developed code GCOMS and Particle-in-Cell (PIC) code MAGIC are used for the mode selection and beam–wave interaction simulations, respectively. The cold cavity analysis and beam–wave interaction computation are carried out to analyze the eigenmode and output power, respectively. A thorough parametric analysis of the interaction cavity geometry and electron beam parameters is also carried out with respect to the output power and frequency. The results show the capability of the interaction cavity, designed for the TE 34,10 mode, to produce more than 1 MW of RF power of a gyrotron at the operating frequency of 170.03 GHz.

NUMERICAL OPTIMIZATION OF PITCH PROFILE FOR OVERALL EFFICIENCY ENHANCEMENT OF A SPACE TWT

Obtaining higher e-ciency during the development of space Traveling Wave Tubes (TWTs) is always one of the most important goals for scientists. In this paper, a scheme of obtaining the maximum theoretical overall e-ciency is explored by optimizing the helix pitch proflle of a TWT based on the collectability of spent beam. The collectability of the spent beam was evaluated by the maximum collector e-ciency, and this maximum collector e-ciency was employed to calculate the maximum theoretical overall e-ciency. The energy distribution of the spent beam and the output power of TWTs were calculated by the 3-D large signal Beam-Wave Interaction Simulator (BWIS) of MTSS. The detailed design of a Ku-band helix TWT is described according to three optimization goals (theoretical overall e-ciency, theoretical collector e-ciency and electronic e-ciency). The simulation results indicate that the optimization for high interaction circuit e-ciency or collector e-ciency by itself is not adequate to obtain maximum overall e-ciency. The maximum theoretical overall e-ciency of 77% was achieved via the optimization of slow wave structure for theoretical overall e-ciency.

Theory and Design of Microwave-Tube Simulator Suite

The development of microwave-tube simulator suite (MTSS) is reported. MTSS is an integrated full-featured software package for microwave-tube analysis and design. It includes a friendly user-interface module and three physics simulators. Microwave-tube design environment is the user-interface module, which provides a powerful solid-modeling front end and graphical and computational postprocessing functionality. Electron optics simulator (EOS) is a fully 3-D finite-element design tool for microwave-tube electron guns and collectors. An EOS is used to design gridded guns, multibeam guns, and anisotropic collectors. A high-frequency circuit simulator is an advanced 3-D electromagnetic (EM) simulation tool for RF components, which has two solution methods based on a finite-integration technique and a finite-element method. Beam-wave interaction simulator (BWIS) is a design tool for electron beam and EM-wave interaction in microwave tubes. The 1-D, 2-D, and 3-D multifrequency nonlinear beam-wave interactions for helix traveling-wave tubes have been implemented in BWIS. The architecture, features, theory, and design of MTSS are presented.

A Method of Numerical Design of Tunneladder Circuits for Millimeter-Wave Traveling-Wave Tubes

In this paper, we have developed an accurate and fast method of predicting the dispersion characteristics, interaction impedance, and attenuation of tunneladder slow-wave structure for millimeter-wave traveling-wave tubes, in which an equivalent circuit theory and the simulations of electromagnetic simulation software are incorporated. The discrepancy between the theoretical data by this approach and the experimental data is within 0.5% on dispersion characteristics. Furthermore, the cold results are used in the nonlinear beam-wave interaction simulation code LATTE to calculate the tube gain. The test results show good agreement with the computer simulated (LATTE) linear and saturated gains.

Theory and simulation of beam-wave interaction of the gyro-peniotron

Starting from the relativistic equation of motion and the energy equation of electron, a largesignal theory, which describes the beam-wave interaction in a gyro-peniotron, is presented in this paper. The theory is valid for arbitrary TEmn modes and arbitrary harmonics of the cyclotron frequency. Numerical simulation shows that under defined conditions an electronic efficiency of about 45% for the third cyclotron harmonic at an operation frequency of 35GHz could be obtained, While the required DC magnetic field is only 4.2kGs. This fact indicates that this device could be efficiently operated at high power level, high efficiency, high frequency and low magnetic field. Therefore, the practical applications of the gyro-device will be greatly extended and the potential for short-millimeter and submillimeter wavelength exists.