Thermal and Structural Analysis and its Effect on Beam-Wave Interaction for 170-GHz, 1-MW Gyrotron Cavity

In this paper thermal and structural analysis for 170 GHz, 1 MW gyrotron interaction cavity and the effect of structural deformation on beam wave interaction is presented. Finite element analysis codes ANSYS has been used for the thermal and structural analysis. Electromagnetic simulator-MAGIC, a Particle-in-Cell (PIC) code, has been used to carry out the effect of the radial expansion of the interaction cavity on beam wave interaction. The change in output power and resonant frequency for operating mode TE_34,10 due to thermal expansion is 10 kW and 0.07 GHz, respectively. These values are under the tolerance limit of power and frequency of the gyrotron. The major variation is found in the power growth stability time.     

Numerical Design of Megawatt Gyrotron with 120 GHz Frequency and 50% Efficiency for Plasma Fusion Application

The design of 120 GHz, 1 MW gyrotron for plasma fusion application is presented in this paper. The mode selection is carried out considering the aim of minimum mode competition, minimum cavity wall heating, etc. On the basis of the selected operating mode, the interaction cavity design and beam-wave interaction computation are carried out by using the PIC code. The design of triode type Magnetron Injection Gun (MIG) is also presented. Trajectory code EGUN, synthesis code MIGSYN and data analysis code MIGANS are used in the MIG designing. Further, the design of MIG is also validated by using the another trajectory code TRAK. The design results of beam dumping system (collector) and RF window are also presented. Depressed collector is designed to enhance the overall tube efficiency. The design study confirms >1 MW output power with tube efficiency around 50% (with collector efficiency).     

Design and Misalignment Analysis of 140 GHz, 1.5 MW Gyrotron Interaction Cavity for Plasma Heating Applications

In this paper the design of 140 GHz, 1.5 MW gyrotron interaction cavity is described in detail. The interaction cavity is designed and simulated by using Particle-in-Cell code for TE_24,8 operating mode. The obtained simulation results show more than 1.5 MW of output power at 139.83 GHz of frequency. A thorough parametric and misalignment study is also presented to support the actual fabrication and assembling of the device.     

Design and preliminary test of a 105/140 GHz dual-frequency MW-level gyrotron

A dual-frequency (105/140 GHz) MW-level continuous-wave gyrotron was developed for fusion application at Institute of Applied Electronics, China Academy of Engineering Physics. This gyrotron employs a cylindrical cavity working in the TE18,7 mode at 105 GHz and the TE24,9 mode at 140 GHz. A triode magnetron injection gun and a built-in quasi-optical mode converter were designed to operate at these two frequencies. For the proof-test phase, the gyrotron was equipped with a single-disk boron nitride window to achieve radio frequency output with a power of ∼500 kW for a short-pulse duration. In the preliminary short-pulse proof-test in the first quarter of 2021, the dual-frequency gyrotron achieved output powers of 300 kW at 105 GHz and 540 kW at 140 GHz, respectively, under 5 Hz 1 ms continuous pulse-burst operations. Power upgrade and pulse-width extension were hampered by the limitation of the high-voltage power supply and output window. This gyrotron design was preliminarily validated.     

Design and Experimental Demonstration of a 94-GHz Gyrotron with Complex Cavity Operating at the Second Harmonic

A systematic theoretical and experimental study on 94-GHz second-harmonic gyrotron with a superconducting magnet system is presented in this paper. A complex cavity with gradual transition is employed in the gyrotron. A self-consistent field nonlinear theory is used and numerical simulation results for electron beam interaction with TE₀₂–TE₀₃ modes are given. A pulse output power of 235.2 kW is obtained by simulation at a beam voltage of 60 kV with beam current of 10 A and magnetic field 17 kG, corresponding to an efficiency of 39.2 %.     

Numerical Analysis of Interaction Cavity for 1.5 MW/127.5 GHz Gyrotron

This paper presents the design of 127.5 GHz ITER start-up gyrotron interaction cavity. Particle-in-Cell electromagnetic simulation approach has been used for the cold cavity and beam-wave interaction analysis. In-house developed code GCOMS has been used for the mode selection. TE_24,8 mode has been chosen as the operating mode. The simulation results show the output power more than 1.5 MW at the operating frequency of 127.8 GHz and the cavity centre magnetic field of 5.1 T. The study of the parametric dependency of the output power and the efficiency on the electron beam and the cavity geometry parameters has also been carried out.     

Design of 84 GHz 500 kW Gyrotron for Technological Millimeter Wave Applications

In this paper, the design and the numerical simulation of the 84 GHz, 500 kW gyrotron at first harmonic operation for technological applications is described. The operating mode of the gyrotron is TE_{10, 4}. Various in-house developed and commercially available computer codes are used for the design purpose. The triode-type magnetron injection gun with the accelerating voltage 70-kV, the beam current 10-A and the maximum transverse velocity spread less than 5% is designed. The preliminary design is obtained by using some trade-off equations. The mode selection, the cold cavity and the beam-wave interaction analysis are discussed for the design of weakly tapered open resonator type of the interaction cavity. The parametric analysis of the interaction cavity and the electron gun is also presented.     

Electron beam emission and interaction of double-beam gyrotron

This paper presents the numerical simulation of a double-beam magnetron injection gun (DB-MIG) and beam-wave interaction for 60 GHz, 500 kW gyrotron. The beam-wave interaction calculations, power and frequency growth estimation are performed by using PIC code MAGIC. The maximum output power of 510 kW at 41.5% efficiency, beam currents of 6 A and 12 A, electron beam velocity ratios of 1.41 and 1.25 and beam voltage of 69 kV are estimated. To obtain the design parameters, the DB-MIG with maximum transverse velocity spread less than 5% is designed. The computer simulations are performed by using the commercially available code EGUN and the in-house developed code MIGANS. The simulated results of DB-MIG design obtained by using the EGUN code are also validated with another trajectory code TRAK, which are in good agreement.     

Time-dependent multi-mode nonlinear theory of dual-frequency operation coaxial gyrotron with two electron beams

The nonlinear coupling between modes and electron beams of the coaxial gyrotron with two electron beams (CGTB) has been investigated by means of the self-consistent time-dependent multi-mode nonlinear theory. The effects of the currents of two electron beams on the output power of two operating modes are discussed. It has been found that CGTB can operate at two different frequencies simultaneously with the given parameters and the peaks of the output power of two operating modes appear alternately with a certain period in dual-frequency operation. Compared with the coaxial gyrotron with one beam (CGOB) with the same parameters, the corresponding average output power of two operating modes in CGTB is enhanced due to the nonlinear coupling between operating modes and electron beams.     

基于脉冲步进调制技术的ECRH全固态阳极高压电源控制系统设计

电子回旋共振管是产生高功率毫米微波的真空电子器件,在可控热核聚变研究、雷达等领域中有重要的应用。针对可控热核聚变研究中1 MW/105 GHz回旋管加热系统阳极电源幅度可调且调制的要求,使用高频开关电源技术和脉冲步进调制技术（PSM）研制了全固态阳极高压电源。重点阐述了阳极高压电源实现稳压、调制、前沿时间可调功能的软件控制算法,并通过实验对设计进行了验证。该阳极高压电源具有单脉冲、多脉冲调制和六电平预置波形等3种模式输出功能;输出参数达到35 kV/200 mA,波形前沿3 ms内可调,最大调制频率为1 kHz,调节精度在100 V以内。设计的控制方法也可应用于其他大功率微波源。     

Gyrotron and its Electron Beam Source: A Review

Microwave occupies a glorious position in the electromagnetic spectrum and in that there are a number of devices in this frequency regime which are capable of high power operations. Among them, gyrotron has proven to be an efficient source for radio frequency (RF) generation at high power level and up to very high frequency. The gyrotron consists of several components like electron beam source, interaction structure, quasi-optical launcher, collector, RF window, magnet system, etc. All the components have their distinct role in the function of the device. Among them, electron beam source also called magnetron injection gun (MIG) is the generator of electron beam and it is very essential that MIG should produce and provide electron beam suitable for the beam-wave interaction at the interaction structure for the effective power growth. The paper presents the introduction of a microwave tube, gyrotron and its components alongwith review of the previous work, the background and the applications. The functions of various components of a gyrotron are discussed with particular highlighting on the electron beam emission from the electron beam source and the beam-wave interaction for power growth in the device. A review on different types of gyrotron electron beam sources is also presented.     

Characteristics of Coaxial Vircator in Three Specific Configurations

As a novel vircator device, the coaxial vircator can attain much higher efficiency than the common virtual cathode oscillator. In this paper, coaxial vircators in three specific configurations are studied to describe the efficiency and frequency characteristics and their dependence on geometric parameters. The PIC (Particle in Cell) simulation results show that a power efficiency over 11% can be obtained from the coaxial vircator with a finite inner anode conductor, and a narrow-band output can be achieved. A direct-coupled coaxial vircator has a slightly lower efficiency of about 8%, but in this configuration the efficiency is not strongly dependent on the geometry parameters. The introduction of a reflecting cavity can effectively improve the efficiency under certain parameters. Meanwhile, the research results also indicate that improper cavity parameters will countervail some inherent advantages of the configuration with a finite inner conductor, leading to lower efficiency than that of the direct-coupled one. Meanwhile, an experiment was also carried out to testify the simulation results, and a power efficiency over 3% was obtained from the direct-coupled coaxial vircator.     

Review of quasi-optical gyrotron development

There is currently a need for megawatt average power sources of 100–600 GHz radiation for electron cyclotron heating of fusion plasmas. One of the leading candidates for such a source, the conventional wave guide cavity gyrotron,⁽¹⁾ has produced impressive output powers and efficiencies at frequencies up to about 300 GHz. However, this gyrotron configuration is limited at high frequencies by high ohmic heating and problems with transverse mode competition due to the highly overmoded configuration, and with beam collection, since the beam must be collected along a section of the output waveguide. The quasi-optical gyrotron (QOG), first proposed in 1980 by Sprangle, Vomvoridis, and Manheimer,⁽³⁾ features an open resonator formed by a pair of spherical mirrors instead of a waveguide resonator and has the potential for overcoming each of these limitations. The resonator mirrors can be well removed from the beam-wave interaction region, allowing a large volume for the interaction and low ohmic heating densities at the mirrors. The beam direction is transverse to the resonator so that beam collection is separate from the output waveguide. This geometry is particularly well suited to the use of a depressed collector for electron beam energy recovery. The QOG operates in the lowest-order transverse (TEM_ool) Guassian mode of the resonator, higher-order transverse modes being effectively suppressed by higher diffraction losses. This paper reviews recent progress toward the development of high-power quasi-optical gyrotrons for ECRH of fusion plasmas. It includes an overview of gyrotron theory in terms of normalized variables as they apply to the quasi-optical gyrotron for operation both in the fundamental and the higher harmonics. Scaling equations for the output power and resonator mirror heating by the RF are given. The design tradeoffs between annular and sheet electron beams are discussed as is the issue of beam space-charge depression in the open resonator. Recent advances in the analysis and design of QOG configurations capable of efficient and stable single-mode operation are discussed, showing the possibility of achieving 50% transverse efficiency in highly overmoded resonators. The application of a depressed collector is discussed as a means of recovering the energy in the axial motion of the spent electron beam and, thus, raising the output efficiency to near the transverse electronic efficiency. The problem of high field magnet design is addressed, for both fundamental and higher harmonic operations, the latter being necessary at very high frequencies. The design equations and tradeoffs are applied to the design of 1-MW, CW quasi-optical gyrotrons operating at 120 GHz, in the first and second harmonic at 280 GHz and in the second harmonic at 560 GHz. The output coupling for these 1 MW designs is 5–7% showing the potential for even higher powers per tube if sheet-beam electron guns can be developed. The estimated electronic efficiency of the fundamental harmonic designs is 23%, which leads to an output efficiency of 47% with the use of a depressed collector with a modest collection efficiency. The peak ohmic heating density is 500 kW/cm² in all the designs. This leads to resonator mirror separations ranging from 127 cm for 120-GHz design, to 232 cm for the 560-GHz, second harmonic design. Finally, a simple output system composed of'elliptical and parabolic mirrors is described that converts the output radiation from the resonator into a parallel, quasi-Gaussian beam. Experimental programs are reviewed as well, including the recent experiment at the Naval Research Laboratory that produced frequencies ranging from 95–130 GHz and powers up to 150 kW. Operation in a single mode was observed at powers up to 125 kW despite the resonator being highly overmoded. Comparison is made with the theoretically-predicted region of single-mode operation. Recent progress in the experimental characterization of QOG resontors is summarized.     

The anode power supply for the ECRH system on the J-TEXT tokamak

The electron cyclotron resonance heating(ECRH) system with a 60 GHz/200 k W/0.5 s gyrotron donated by the Culham Science Center is being developed on the J-TEXT tokamak for plasma heating, current drive and MHD studies. Simultaneously, an anode power supply(APS) has been rebuilt and tested for the output power control of the gyrotron, of which the input voltage is derived from an 80 k V negative cathode power supply. The control strategy by controlling the grid voltage of the tetrode TH5186 is applied to obtain an accurate anode climbing voltage, of which the output voltage can be obtained from 0-30 k V with respect to the cathode power supply. The characteristics of the APS, including control, protection, modulation, and output waveform, were tested with a100 k V/60 A negative cathode power supply, a dummy load and the ECRH control system. The results indicate that the APS can meet the requirements of the ECRH system on J-TEXT.     

耦合腔行波管三维整管模拟

电子枪是耦合腔行波管的核心部件之一，枪的电子束参数对行波管工作性能有重要影响。在使用PIC软件设计一S波段耦合腔行波管时，对电子枪进行了数值模拟，构建了行波管的三维整管计算模型，该模型包含电子枪、慢波结构、微波输入输出耦合器等部件，模拟了该S波段行波管整管的大信号注波互作用过程。模拟结果表明：在2.0~2.3GHz工作频带内，该行波管的连续波输出功率达5.9kW，效率为24%。整管模拟为行波管设计提供了依据。     

阵列式低功耗Si-PIN个人剂量仪设计

采用瑞士TEVISO的阵列式Si-PIN探测器探测X、γ射线;以低功耗PIC单片机为核心,设计了低功耗电源转换电路、一键开关机电路、按键与LCD显示、蜂鸣器等,并采用多种单片机软件设计方法降低功耗。该个人剂量仪具有脉冲计数、剂量当量率实时显示及存储,可查看测量时间与历史数据,报警阈值设置与报警等功能。     

Room-temperature test system for 162.5 MHz high-power couplers

Fundamental power couplers are crucial components for feeding radio frequency power to accelerating cavities. Couplers must be tested and conditioned on a room-temperature test stand to evaluate and potentially improve their performance before being installed in an accelerating cavity. A new test system has been designed and is under construction at the institute of modern physics.For this test system, multiple conditioning modes, including the pulse mode, CW mode, and amplitude-sweeping mode, have been embedded in the low-level radio frequency system of the test stand. All of these conditioning modes can be run manually or automatically. In addition, a novel test cavity is proposed and has been designed, which facilitates non-contact conditioning and a multi-purpose test stand.     

行波电子直线加速器稳频系统的鉴频方法

稳频系统的频率稳定度取决于谐振腔体的有载品质因素。因电子直线加速器的功率源是脉冲磁控管，其功率谱为形状，无限增大品质因素是不正确的，由帕息维尔定理知道腔体平方律检波器输出信号的面积正比于腔体输出能量，于是当磁控管振荡频率改变时，该信号面积的变化等效于腔体输出能量的变化，根据上述原理获得了品质因素的上限和推荐表达式。     

250MHz固态功率放大器的设计

固态功率源代替真空管功率源设备是目前射频功率源系统的发展趋势。本文介绍了一台工作在250 MHz的固态功率放大器模块的设计过程。放大器模块使用荷兰恩智浦半导体公司生产的BLF578XR型号晶体管,并且采用传输线匹配和集总元件匹配相结合的方式进行设计。通过理论计算得到匹配网络的初始值,并利用ADS(Advanced Design System)软件对匹配电路进行仿真和优化。测试结果表明,该功率放大器模块输出功率达到了850 W,功率增益达到了26 d B,功率附加效率达到60%。结果表明,该设计完全达到了系统设计要求的性能指标,并具有较强的实用性。