螺旋线行波管返波自激振荡的研究

 在2维小信号模型的基础上，分析了均匀和周期永久聚焦磁场对抑制返波自激振荡的影响。研究结果表明：改变聚焦磁场的幅值或周期来增加起振长度是可能的， 而且不会改变基波的互作用条件。与此同时，对起振长度、初始非同步速度参量随皮尔斯增益参量、空间电荷参量、损耗参量等的变化，以及在超宽带行波管中当存在两个或多个角向非对称空间谐波时,起振长度、初始非同步速度参量随周期永久聚焦磁场的变化进行了研究。优化设计聚焦磁场、电子注和螺旋线慢波系统的参量可以对螺旋线行波管的稳定性分析提供必要的依据。     

毫米波静电聚焦行波管电子光学系统的设计

介绍了静电聚焦方式在毫米波行波管中的独特优势,分析了周期静电聚焦场的建立方法。基于某Ka波段行波管,首先根据指标要求设计了强流电子枪并选择类梳齿状结构作为其慢波电路,然后对电子枪和类梳齿状慢波电路组成的电子光学系统进行了模拟计算,最后对慢波电路的关键尺寸进行了容差分析。结果显示,在周期静电场的作用下,电子注全部平稳地通过了慢波系统。良好的静态通过率为后续高效率的注-波互作用奠定了基础,证明了利用静电场聚焦毫米波行波管中大电流密度电子注的可行性。     

基于电子注可回收能力的空间行波管慢波结构的优化设计

探索了一种行波管效率提高的优化设计方法.该方法在不降低电子效率的前提下,对慢波结构进行优化以获得互作用后电子注能量台阶状的分布,为研制高回收效率的收集极奠定基础.提出了用最大可回收效率表示的目标函数来衡量电子注的可回收能力.与单纯以电子效率为目标的慢波结构优化相比,以电子注可回收能力最大化为目标的慢波结构优化,不仅能在工作频带内提高总效率,而且行波管的非线性指标没有明显降低,小信号增益却有较大的提高. 关键词： 空间行波管 可回收能力 慢波结构 优化设计     

基于双排矩形梳状慢波结构的W波段宽频带行波管模拟研究

提出采用圆形电子注和双排矩形梳状慢波结构作为W波段宽频带行波管注波互作用回路. 对该慢波回路的"冷"态特性、输入输出结构等方面进行了模拟仿真和分析, 研究结果表明, 该结构色散特性较好, 带宽较宽; 通过调整双排矩形梳状慢波结构之间的距离和电子注通道半径的尺寸, 圆形电子注系统取得了和带状注系统相同的耦合阻抗; 且该结构传输特性较好, 优化后整管的驻波比能在较宽的频带内保持在2以下. 此外, 对该慢波系统的大信号理论计算和PIC粒子模拟结果一致. 在50 mW驱动功率下, 输出功率在10 GHz带宽内大于40 W, 增益高于29 dB.     

周期永磁聚焦电子注性能计算机模拟

 使用全三维电磁场粒子模拟程序MAFIA建立了行波管周期永磁聚焦系统模型，计算了磁系统中的磁场分布和静态电子注传输特性。分析了周期永磁系统聚焦电子注传输特性，并重点讨论了磁场强度、磁场端部效应和横向速度分布对电子注聚焦性能的影响。为周期永磁聚焦系统的工程设计和优化提供了有价值的模拟结果。     

开敞型角向周期加载金属柱圆波导的注波互作用线性理论研究

提出了一种可应用于毫米波功率放大器中的新型慢波结构——-开敞型角向周期 加载金属柱圆波导结构,并且在互作用通道内,引入了薄环形电子注, 推导出了此时的"热"色散方程,并且对基于该新型慢波结构的行波管的 小信号增益特性进行了深入探讨.通过数值方法 研究了金属柱尺寸和电子注参数 对器件线性特性的影响. 结果表明: 通过对金属柱尺寸的适当设计, 可以获得更高的增益值. 与封闭型结构的比较结果表明, 开敞型角向周期加载金属柱圆波导结构能够 有效地提高小信号增益, 并且对带宽的影响不大. 研究结果为研制基于此新型慢波系统的毫米波行波管奠定了理论基础.     

螺旋线行波管慢波结构设计及注波互作用模拟

通过模拟计算,分析螺旋线内径和螺距变化对色散和耦合阻抗的影响,优化慢波结构,初步设计了Ku波段螺旋线行波管慢波结构。模拟行波管输入输出结构,得到输入端反射系数小于-19 dB,电压驻波比小于1.24。电子聚焦系统采用周期永磁聚焦,磁场周期为8.5 mm,计算得到磁场峰值为0.17 T。为提高注波互作用效率,采用具有动态速度渐变特性的慢波结构,使得电子注与高频场有足够的互作用时间,从而保证电子不断地将能量交给高频场。运用三维PIC粒子模拟软件分析行波管的注波互作用,得到在12.5~16 GHz频率范围内输出功率大于88.7 W,电子效率大于14.8%,增益大于34.6 dB。     

变周期大结构低压工作折叠波导行波管的理论与模拟研究

为解决工作在3 mm波段及以上频段的折叠波导行波管因加工精度和功率容量的局限性, 提出了非渐变型有限变周期折叠波导慢波结构. 首先给出了这种结构能够有效增大高次空间谐波耦合阻抗的理论基础, 并导出了色散和耦合阻抗表达式; 然后进行数值计算, 给出一组优化后的设计参数, 并以此确定行波管的工作点; 最后利用MAFIA粒子模拟软件进行大信号互作用模拟, 获得有效增益. 在结构和周期都比较大的情况下, 实现了相对工作电压比较低的行波管设计. 关键词： 折叠波导 变周期 高次模式 行波管     

同轴膜片加载圆波导相对论行波管注-波互作用线性理论研究

 从改善圆盘加载波导作为相对论行波管慢波结构的特性入手，加入同轴内导体，着重研究其小信号理论。利用场匹配法导出了“热”色散方程并计算求解，具体分析了系统的电子注参量及慢波结构几何尺寸对小信号增益及慢波相速的影响,为同轴圆盘加载相对论行波管的设计提供了理论基础。     

相对论行波管色散特性分析

 数值计算了一种填充等离子体的波纹波导结构的行波管，在强引导磁场下，被一环形相对论电子注驱动的小信号增益。详细地分析了等离子体的浓度、电子注的电压、电流及其在慢波结构中的传输位置对行波管的增益、带宽和中心频率的影响。     

Field theory of dielectric Cherenkov maser

The effect of three-dimensional perturbed velocity and three-dimensional perturbed current density on the beam-wave interaction of dielectric Cherenkov maser is analysed by use of the self-consistent linear field theory. Three distinct cases are considered. First, the propagation of the electron beam in an annular dielectric liner enclosed by a loss-free conducting wall is investigated. The dispersion equation and the simultaneous condition of the beam-wave interaction are derived. It's clearly shown that the instability of the interaction results from the coupling of the TM mode in the dielectric lined slow-wave waveguide to the beam mode via the electron beam. And the coupling is proportional to the density of the beam. The growth rate of the wave produced by the electron beam are obtained. Then, the case of a relativistic electron beam guided by a longitudinal magnetic field in the same slow-wave structure is examined. The motion of electrons could be approximated to be one-dimensional when the simultaneous condition of the beam-wave interaction of dielectric Cherenkov maser is satisfied. Finally, the effect of the background plasma on the instability of the beam-wave interaction is studied.This work is supported by National Natural Science Foundation of China.     

The study of synchronization in the periodic nonuniform folded waveguide

The periodic nonuniform folded waveguides are special structures, the physical dimension of which is between the periodic folded waveguide and the tapering period folded waveguide. Therefore, the synchronization between the microwave and the electron beam can be maintained in the whole interaction process and the periods are not tapered. In comparison with the tapering period folded waveguide, the theoretical analysis and the technological requirements for this structure are more convenient. In order to study this structure, the space harmonics are analysed, the conditions to make the m-th space harmonic synchronizing with the electron beam in the whole interaction process are present, and the dispersion curve and the coupling impedance curve are obtained by the simulation software HFSS.     

低磁场S波段相对论返波振荡器的工作特性

为了实现高功率微波发生器的小型化,开展了S波段低磁场相对论返波振荡器工作特性的研究工作。由于S波段返波振荡器频率低,对应的电子回旋共振磁场强度也很低,因此低磁场条件下面临着电子束传输效率低和束波互作用效率低两大问题。为解决上述问题,采取下列措施:通过加大电子束与器件内壁的距离,提高电子束传输效率;采用较深的慢波结构作为提取腔,实现高束波互作用阻抗;提取腔前采用浅深度慢波结构,使提取腔区域的电子速度与微波相速同步。粒子模拟证明,以上措施有效,在引导磁场强度仅为0.17 T、电子束电压435 kV、电流6.5 kA的条件下,该返波管获得功率为670 MW、效率约为25%的输出微波。相对于常规S波段相对论返波振荡器的磁场系统(B=0.8 T),适用于该返波管的0.17 T低强度磁场系统螺线管外半径下降了20%,能耗下降了约93.8%。     

A Particle-in-Cell Simulation Study on Harmonic Waves Excited by Electron Beams in Unmagnetized Plasmas

The excitation of harmonic waves by an electron beam is studied with electrostatic simulations.The results suggest that the harmonic waves are excited during the linear stage of the simulation and are developed in the nonlinear stage.First,the Langmuir waves(LWs)are excited by the beam electrons.Then the coupling of the forward propagating LWs and beam modes will excite the second harmonic waves.The third harmonic waves will be produced if the lower velocity side of the beam still has a positive velocity gradient.The beam velocity decreases at the same time,which provides the energy for wave excitation.We find that it is difficult to excite the harmonic waves with the increase of the thermal velocity of the beam electrons.The beam electrons will be heated after waves are excited,and then the part of the forward propagating LWs will turn into electron acoustic waves under the condition with a large enough intensity of beam electrons.Moreover,the action of ions hardly affects the formation of harmonic waves.     

Development of the method for determining the electron velocity in a gyrotron

We have analyzed the possibility of determining the electron velocity using the data on propagation of a microwave low-power signal in a slow-wave system located in the region of electron beam formation. The diagnostic section is designed for implementing this method in an experimental gyrotron with a working frequency of 74.2 GHz and an output power of 100 kW. Numerical simulation shows that information on the longitudinal velocity of electrons can be obtained from an analysis of the frequency dependence of the amplification factor for a signal propagating in the slow-wave system at frequencies in the gigahertz range.     

On the possibility of natural formation of a transverse wave with a phase velocity lower than the velocity of light

The formation of a transverse wave with a phase velocity lower than the velocity of light, which can exist in an equilibrium plasma without a slow-wave structure in zero magnetic field, is described. It involves the transformation of a transverse wave with trapped electrons, traveling along the magnetic field, into a slow transverse wave after the removal of the magnetic field. During the evolution of the wave with trapped electrons, the magnetic induction decreases very slowly in the direction of the wave propagation. As a result, the velocity at which electrons are in resonant interaction with the wave increases; therefore, the electrons fall to the bottom of potential wells. Under the influence of the trapped electrons, the phase velocity of the wave decreases and becomes lower than the velocity of light. It becomes equal to the velocity at which the electrons are in resonance interaction with the wave at the instant when the magnetic field vanishes. It is demonstrated that a transverse wave with a velocity lower than the velocity of light can exist in an equilibrium plasma even after the magnetic field vanishes; in this case, the flow of trapped electrons serves as a slow-wave structure.     

未磁化等离子体介质切连科夫脉塞的线性理论

利用线性自洽场理论，讨论了电子在扰动场作用下的三维扰动．在此基础上，对常用的薄环形相对论电子环束在填充未磁化等离子体的介质筒慢波波导中激励的切连科夫辐射进行了详细的分析，导出了此电子环束与慢波系统中任意波导模互作用的色散方程和波增长率，并对其进行了详细的分析和讨论．分析表明切连科夫辐射是由其波导模与电子注模耦合所致．最后详细计算和分析了等离子体密度对色散特性和波增长率的影响 关键词：     

The nonlinear theory of slow-wave electron cyclotron masers with inclusion of the beam velocity spread

The nonlinear theory of slow-wave electron cyclotron masers (ECM) with an initially straight electron beam is developed. The evolution equation of the nonlinear beam electron energy is derived. The numerical studies of the slow-wave ECM efficiency with inclusion of Gaussian beam velocity spread are presented. It is shown that the velocity spread reduces the interaction efficiency.     

Observation of the second harmonic in Thomson scattering from relativistic electrons

A free relativistic electron in an electromagnetic field is a pure case of a light-matter interaction. In the laboratory environment, this interaction can be realized by colliding laser pulses with electron beams produced from particle accelerators. The process of single photon absorption and reemission by the electron, so-called linear Thomson scattering, results in radiation that is Doppler shifted into the x-ray and gamma-ray regions. At elevated laser intensity, nonlinear effects should come into play when the transverse motion of the electrons induced by the laser beam is relativistic. In the present experiment, we achieved this condition and characterized the second harmonic of Thomson x-ray scattering using the counterpropagation of a 60 MeV electron beam and a subterawatt CO2 laser beam.