Linear theory of a dielectric-loaded rectangular Cerenkov maser with a sheet electron beam

A three-dimensional model of a dielectric-loaded rectangular Cerenkov maser with a sheet electron beam for the beam-wave interaction is proposed.Based on this model,the hybrid-mode dispersion equation is derived with the Borgnis potential function by using the field-matching method.Its approximate solution is obtained under the assumption of a dilute electron beam.By using the Ansoft high frequency structural simulator(HFSS) code,the electromagnetic field distribution in the interaction structure is given.Through numerical calculations,the effects of beam thickness,beam and dielectric-layer gap distance,beam voltage,and current density on the resonant growth rate are analysed in detail.     

一种矩形截面切伦柯夫脉塞金属周期慢波结构的分析方法

 分析了矩形截面切伦柯夫脉塞周期金属慢波结构的色散特性,以及结构参数的变化对色散曲线的影响。为避免慢波结构两端突变引起的反射振荡,采用等效电路法分析了用于连接光滑波导和慢波结构的渐变段。将线性形、两段形和指数形的渐变段进行了比较。指数形渐变段末端的功率反射系数最小, 并且整体的变化最平缓, 因此可将其作为实现慢波与快波间转换的较优选择。分析了频率和实际加工误差对指数形渐变段功率反射系数的影响:在频率较小时,功率反射系数也较小;固定频率下,较小的加工误差能使交界处功率反射系数的变化较平缓。在此基础上设计了一个功率反射系数小于0.01的指数渐变段,实现了工作模式和快波模式之间的良好匹配。与耦合模理论分析方法相比,等效电路方法更为简洁,二者结果相符合。     

Linear analysis of a three-dimensional rectangular Cerenkov maser with a sheet electron beam

A linear theory of a rectangular Cerenkov maser (RCM) with a sheet electron beam is developed by using the field-match method. Based on the three-dimensional beam-wave interaction model proposed in this paper, a hybrid-mode dispersion equation and its analytical solution are derived for the RCM. Through numerical calculations, the effects of the beam-grating gap, beam thickness, current density, beam voltage and waveguide width on the linear growth rate are analysed. Moreover, the performance difference between the RCM with the closed transverse boundary and that with the upper open boundary is compared. The results show that the closed RCM model can avoid the effect of RF radiation on beam-wave interaction, which is more rational for practical applications.     

介质加载的矩形截面Cerenkov脉塞中带状电子注与慢波结构互作用的研究

本文建立了介质加载的矩形截面Cerenkov脉塞中带状电子注与慢波结构互作用的三维物理模型. 采用Borgnis函数法和场匹配法求解了多层介质中场的匹配问题, 获得了注波互作用结构的混合模热色散方程(含电子注)及其近似解. 通过数值计算, 分析了热态下介质层厚度、电子注电压、电流密度、电子注厚度及电子注与 介质层间隙距离等主要结构和电参数对注波互作用增长率的影响.     

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.     

一种矩形截面切伦柯夫脉塞金属周期慢波结构的分析方法

分析了矩形截面切伦柯夫脉塞周期金属慢波结构的色散特性,以及结构参数的变化对色散曲线的影响。为避免慢波结构两端突变引起的反射振荡,采用等效电路法分析了用于连接光滑波导和慢波结构的渐变段。将线性形、两段形和指数形的渐变段进行了比较。指数形渐变段末端的功率反射系数最小, 并且整体的变化最平缓, 因此可将其作为实现慢波与快波间转换的较优选择。分析了频率和实际加工误差对指数形渐变段功率反射系数的影响:在频率较小时,功率反射系数也较小;固定频率下,较小的加工误差能使交界处功率反射系数的变化较平缓。在此基础上设计了一个功率反射系数小于0.01的指数渐变段,实现了工作模式和快波模式之间的良好匹配。与耦合模理论分析方法相比,等效电路方法更为简洁,二者结果相符合。     

Analysis and design of the taper in metal-grating periodic slow-wave structures for rectangular Cerenkov masers

The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods.An equivalent-circuit model for the taper of the groove depth that matches the smooth waveguide to the metal-grating structure is proposed.By using the equivalentcircuit method,as well as the Ansoft high frequency structure simulator(HFSS) code,an appropriate electromagnetic mode for beam-wave interaction is selected and the equivalent-circuit analysis on the taper is given.The calculated results show that a cumulative reflection coefficient of 0.025 for the beam-wave interaction structure at a working frequency of 78.1 GHz can be reached by designing the exponential taper with a TE z10 rectangular waveguide mode as the input and the desired TE x10 mode as the output.It is worth pointing out that by using the equivalent-circuit method,the complex field-matching problems from the traditional field-theory method for taper design can be avoided,so the taper analysis process is markedly simplified.     

电子束电流对介质切伦科夫脉塞色散关系的影响

采用等离子体流体理论,从线性扰动方程出发,研究了电子束电流大小对介质切伦科夫脉塞中束波相互作用色散关系的影响,得到了当等离子体返回电流能有效中和与不能有效中和电子束电流两种情形下色散关系和波的增长率,并讨论了电子束电流对束波相互作用色散关系和波增长率的影响。研究表明,等离子体返回电流能有效中和与不能有效中和电子束电流两种情况下有着不同的色散关系和波的增长率。在波导参数和背景等离子体参数固定的情况下,电子束电流并不是越大越好,电子束电流过大不利于提高器件效率,它们之间存在最佳匹配关系。     

电子束电流对介质切伦科夫脉塞色散关系的影响

采用等离子体流体理论,从线性扰动方程出发,研究了电子束电流大小对介质切伦科夫脉塞中束波相互作用色散关系的影响,得到了当等离子体返回电流能有效中和与不能有效中和电子束电流两种情形下色散关系和波的增长率,并讨论了电子束电流对束波相互作用色散关系和波增长率的影响。研究表明,等离子体返回电流能有效中和与不能有效中和电子束电流两种情况下有着不同的色散关系和波的增长率。在波导参数和背景等离子体参数固定的情况下,电子束电流并不是越大越好,电子束电流过大不利于提高器件效率,它们之间存在最佳匹配关系。     

Linear theory of an electron cyclotron maser operating at the fundamental

The linear theory of an electron cyclotron maser (ECM) operating at the fundamental is developed. A set of analytic expressions, valid for all TE cavity modes, is derived for the starting current and frequency detuning using the Vlasov-Maxwell equations in the weakly relativistic limit. These results are applicable for an arbitrary electron velocity distribution as well as any longitudinal distribution of the RF field. It is shown that the starting current can be expressed in a simple form which contains the Fourier trans-form of the longitudinal field distribution. Analytic results are presented for specific longitudinal field variations, including uniform, sinusoidal, and Gaussian. It is found that the starting characteristics of an ECM are strongly influenced by the axial dependence of the RF field, but weakly affected by the velocity spread of the electron beam. The problem of multimode oscillation is treated in the linear theory by using a Slater expansion of the cavity field. The complete formulation for mode competition based on this expansion is presented and preliminary results are derived. This comprehensive analysis of ECM linear theory should be useful as a diagnostic of ECM performance and should facilitate comparison between theory and experiment.Work supported by U.S.D.O.E. Contract DE-AC-02-80ER52059Supported by U.S. Department of EnergySupported by National Science Foundation     

离子通道电子束回旋脉塞的等离子体波效应

研究了离子通道回旋电子束脉塞（ICECM）中的等离子体波非线性效应。利用流体理论与自洽非线性理论方法对ICECM中等离子体波效应的微观机理进行了分析。研究发现,等离子体波加强了电子束的纵向群聚,束-波互作用的能量交换效率及系统增益得到明显提高。数值模拟计算表明,对于中等等离子体密度、1.5kA电流和1MV加速电压的电子束,系统能够获得的脉冲功率和频率分别为200MW和280GHz的毫米波束。     

On the kineteic theory of electron cyclotron maser

This paper starts from the kinetic theory to expound the method of characteristics. Influence of the equilibrium distribution functionf _o upon analyzed result is fully investigated. Dispersion equation is rigorously derived in waveguide coordinate system in case of interaction between TE _mn field in a circular waveguide and a single momentum ring-shaped electron beam. In the meantime, we make some critical review of previous papers and clarify their confusion and ambiguities.     

高功率微波弯曲矩形波导设计

 利用模式耦合理论,在理论推导出弯曲矩形波导TE01模和高阶模之间耦合系数显式表达的基础上,对弯曲矩形波导进行了实例研究。HFSS软件数值仿真结果表明：设计的矩形波导TE01-TE02模式转换器在9.5 GHz转换效率达到99.9%,转换效率大于90%的工作带宽为8.60～10.48 GHz;设计的弯曲矩形波导传输线,可有效传输TE01模,不激励起高阶模式。HFSS数值仿真结果验证了所设计的传输线工作带宽和功率容量均能够满足使用要求。     

Powerful millimeter-wave generators based on the stimulated Cerenkov radiation of relativistic electron beams

Effective relativistic Cerenkoy generators of various types were studied experimentally: orotrons, surface wave oscillators, and Smith-Purcell free-electron masers that were first realized. Single-mode generation was obtained in multimode systems using electrodynamic and electron methods of mode selection. The power obtained in this regime was 100 MW at 8.6 mm with the efficiency 10%, 50 MW at 5.5 mm with the efficiency 5%, and 8 MW at 2.4 mm with the efficiency 3%. In a multimode regime the power of 0.5 MW was obtained at 0.9 mm. The study of the dependence of the generation power on the value of the focusing magnetic field revealed the presence of zones of cyclotron power absorption, that were earlier observed in centimeter-wave generators.     

Matrix coupled mode theory model of strongly-coupled multiwaveguide optical nonlinear directional couplers

This paper discusses an improved coupled mode theory model for the nonlinear directional coupler in the strong-coupling range. A new single-line matrix equation is derived for the multiwaveguide case. For the two-guide case, a new critical power formula and two exact identities are derived. Interrelation between the overlap integral and nonlinear cross-coefficients is demonstrated. It is shown that inconsistent inclusion of these terms in previous approaches leads to inaccuracies. Results obtained by consistent inclusion of these terms and our critical power formula show a great improvement in accuracy over previous analyses in strong-coupling.     

Linear analysis of an axially grooved rectangular gyrotron for harmonic operation

In an axially grooved rectangular waveguide the linearized Vlasov equation is solved to find the perturbed distribution function resulting from the electromagnetic forces on the electrons. The resulting beam current and the propagating electromagnetic waves of the cold tube are used in the inhomogeneous Maxwell's equation to derive the general dispersion equation. This equation is then transformed into the electron beam frame and the resulting linear growth rate of amplification is calculated. By maximizing the linear growth rate, the operational parameters of the gyrotron are then optimized.Work supported in part by NASA Lewis Research Center, Cleveland, Ohio     

Quantum theory of nonlinear processes

Principles of development of the quantum theory of nonlinear processes on the basis of Lagrangian formulation are discussed. It is shown that in the framework of this formulation it is possible to preserve succession from the classical theory and, in particular, use these methods for studies of quantum systems. The quantum dispersion of a nonlinear oscillator excited by an external source and of a parametric generator is calculated. Its role is established in the solution of the problem of stability of oscillations.     

高功率微波弯曲矩形波导设计

利用模式耦合理论,在理论推导出弯曲矩形波导TE01模和高阶模之间耦合系数显式表达的基础上,对弯曲矩形波导进行了实例研究。HFSS软件数值仿真结果表明：设计的矩形波导TE01-TE02模式转换器在9.5 GHz转换效率达到99.9%,转换效率大于90%的工作带宽为8.60～10.48 GHz;设计的弯曲矩形波导传输线,可有效传输TE01模,不激励起高阶模式。HFSS数值仿真结果验证了所设计的传输线工作带宽和功率容量均能够满足使用要求。     

A dielectric rod waveguide coupled with metal rectangular waveguide

Measurements have been done in the millimeter wave region on a composite waveguide which comprises a dielectric rod waveguide connecting two metal rectangular waveguides. Such a waveguide has been used by us in a Josephson harmonic mixer installed in a small metal cryostat, to prevent the thermal invasion from outside environment and to transmit both signal and LO waves with small losses. The measured transmission loss, that is caused mainly by the coupling loss between metal rectangular waveguides (TE₁₀ mode) and a dielectric rod waveguide (HE₁₁ mode), has been less than 2dB in the frequency range of 52–104 GHz.     

Optical bistability of planar metal/dielectric nonlinear nanostructures

We study theoretically a nonlinear response of the planar metal/dielectric nanostructures constituted from periodical array of ultra thin silver layers and the layers of Kerr-like nonlinear dielectric. We predict hysteresis-type dependences of the components of the tensor of effective dielectric permittivity on the field intensity allowing the change in material transmission properties from transparent to opaque and back at extremely low intensities of the light. It makes possible to control the light by light in all-optical nanoscale devices and circuits.