Linear Theory of Plasma-Filled Coaxial Cylindrical Cherenkov Maser

Injection of background plasma into the beam-wave interaction region can greatly enhance the beam-wave interaction efficiency and the microwave output power of the device. In this paper, a new type of plasma-filled slow-wave structure, i.e., plasma-filled, dielectric-loaded coaxial cylindrical waveguide with a dielectric ring enclosing tightly the inner conductor, is developed. The Cherenkov radiation excited by the beam-wave interaction in the slow-wave structure is examined by use of the self-consistent linear field theory. The dispersion equation and the synchronized condition of the beam-wave interaction are derived. It's clearly shown that the Cherenkov radiation excited by the beam-wave interaction results from the coupling between the slow electromagnetic wave, TM-modes, propagated along the slow-wave structure and the negative-energy space-charge wave propagated along the relativistic electron beam. And the wave growth rate is solved, and the beam-wave energy exchange in the presence of the background plasma is discussed. Finally, the effects of the background plasma density on the dispersion characteristics, the distribution of the longitudinal fluctuating electric field, the wave growth rate and the beam-wave energy exchange are calculated and discussed.     

Cherenkov radiation with arbitrary azimuthal mode number excited in a plasma-filled slow-wave waveguide

On the basis of the reference [1], excitation of Cherenkov radiation with arbitrary azimuthal mode number by a thin annular relativistic electron beam in a plasma-filled dielectric-lined slow-wave waveguide is studied in this paper. A determinantal dispersion equation is obtained. This general dispersion equation is valid for arbitrary azimuthal mode number, and the growth rate of the wave is derived from it. Finally, the effects of the background plasma density on the dispersion relation, the background plasma density and the electron beam radius on the growth rate of the wave are presented. Formulas and results offerd in this paper are general, and are of particular value of reference to the beam-wave interaction in azimuthally unsymmetrical slow-wave waveguide.     

Excitation of microwave by an annular electron beam in a plasma-filled dielectric lined waveguide

An axial relativistic electron beam passing through a slow wave structure is unstable to an electromagnetic perturbation whose phase velocity equals the velocity of the beam. This phenomenon of Cherenkov emission is the basis of all traveling wave tubes. In this paper an excitation of Cherenkov radiation by a thin annular relativistic electron beam in a plasma-filled dielectric-lined waveguide is analysed by use of the self-consistent linear theory. The effect of the thin annular electron beam on the beam-wave interaction is completely described by a jump condition. The dispersion equation and the simultaneous condition of the beam-wave interaction are derived. Finally, the growth rate of the wave is obtained, and the effect of the background plasma density and the electron beam radius on the growth rate of the wave are presented.     

PLASMA-FILLED DIELECTRIC CHERENKOV MASER WITH A LONGITUDINAL MAGNETIC FIELD

The use of a background plasma in a dielectric Cherenkov maser can effectively increase the efficiency and the microwave output power of the device. Here, the effect of the longitudinal uniform magnetic field on the wave-beam interaction of the plasma-filled dielectric Cherenkov maser is examined by solving the beam-plasma, dielectric lined waveguide dispersion equation. And the effects of the longitudinal magnetic field, plasma density and dielectric parameters on the linear spatial growth rate and the energy ratio are presented.     

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.     

Instabilities Driven by an Intense Beam in a Plasma-Filled Dielectric-Lined Waveguide Immersed in a Finite Axial Magnetic Field

A linear analysis is described on stabilities driven by an intense relativistic electron beam in an infinitely long, plasma-filled, and dielectric-lined circular waveguide immersed in a finite strength axial magnetic field. A dispersion equation is derived from the cold fluid theory and solved numerically. Beam-plasma instabilities due to interaction between beam modes and the Trivelpiece-Gould modes appear as well as the Cherenkov and the cyclotron Cherenkov instabilities. Parametric researches are carried out varying magnetic field strength, plasma density, and dielectric constant. Effects of a finite magnetic field and plasma filling are discussed in connection with the possibilities of using this system as a microwave radiation source.     

考虑纵向磁场的等离子体介质切伦可夫脉塞

在介质切伦可夫脉塞中加入背景等离子体可有效地提高器件的效率和微波输出功率。本文通过求解束-等离子体、内衬介质的波导色散方程,重点分析了纵向均匀磁场对等离子体介质切伦可夫脉塞注波互作用的影响,给出了磁场、等离子体密度、介质参量等对线性空间增长率和能量比的影响曲线。     

环形相对论电子注激励的等离子体介质切伦可夫脉塞

利用自洽线性场理论，考虑电子的三维扰动，分析了环形相对论电子注在填充背景等离子体的介质筒慢波波导产生的切伦可夫辐射，其环形电子注对主波互作用的作用完全要用一跳变条件来描述，导出了其色散方程和波波互作用的同步条件，求得了是子注产生的波增长率，分析了背景等离子体密度和电子注半径对波增长率的影响。     

考虑回旋共振增强效应的平面单栅注波互作用线性分析

基于电子注纵横运动与电磁场纵横分量同时同步相互作用,该文从麦克斯韦方程和线性伏拉索夫方程出发,推导出将回旋共振和契伦科夫共振同时考虑在内的平面单栅注波互作用热色散方程。在合理选择几何参数和电参数的基础上,通过热色散方程数值计算和分析,发现具有回旋共振增强效应下的注波互作用增益和频带都高于只有契伦科夫共振辐射下的结果。     

Particle-In-Cell Simulations from a X Band Coaxial Relativistic Backward Wave Oscillator

A high-power x-band coaxial relativistic backward wave oscillator has been conceptually designed and analyzed. The TM_on dispersion relations in the coaxial corrugated cylindrical waveguide used in the device was calculated. MAGIC,an electronmagnetic particle-in-cell code, is being used to investigated the nonlinear beam-wave interaction and other design optimization issues. Preliminary simulation results shows that the coaxial BWO can generate 2. 2 GW peak power microwave at 10. 15GHz in the TM₀₂ mode driven by a 600-KV 20-KA electron beam, the peak power efficiency is about 18%.     

实心注在等离子体介质筒产生的切伦可夫辐射

利用自洽线性场理论：考虑电子的三维扰动，分析了轴向实心相对论电子注通过填充背景等离子体介质筒慢波波导产生的切伦可夫辐射，导出了描述其不稳定性的色散方程和注液互作用的同步条件，求得出电磁波辐射的时间增长率，分析了背景等离子体密度和实心电子注半径对波增长率的影响。     

Design and Characterization of a W-Band Folded-Waveguide Slow-Wave Structure

A single-section slow-wave structure for a W-band folded-waveguide traveling-wave tube with operating bandwidth of around 4% was designed for delivering the output power of 50 W at the operating voltage of 13.5 kV and operating beam current of 80 mA. The design was carried out using analytical formulations and 3D electromagnetic simulations. The beam-wave interaction analysis was carried out using large signal Lagrangian analysis and particle-in-cell simulation. The folded-waveguide slow-wave structure along with input-output couplers and RF windows were fabricated. Cold test measurements were carried out for dispersion characteristics of the slow-wave structure and voltage standing-wave ratio and insertion loss characteristics of the RF window. The measured cold circuit parameters show close agreement with the analysis.     

同轴内导体盘荷慢波结构注波互作用机理研究

采用理论分析和粒子模拟方法研究同轴内盘荷慢波结构注波互作用的物理机理。采用场匹配理论得到色散方程,通过数值计算得到了准TEM模的色散曲线及不同电子注电压下注波互作用的增长率;采用粒子模拟技术研究了注波互作用的物理过程。结果表明,随着电子注电压的不断增加,器件的工作状态由返波振荡转换到行波振荡;通过对辐射谱特性进行分析表明粒子模拟结果与理论计算结果基本一致。     

填充环形等离子体的介质切伦可夫脉塞

利用线性场理论,对填充环形等离子体的介质切伦可夫脉塞进行了详尽的分析;讨论了薄环形相对论电子注包围环形等离子体、处于环形等离子体之间和位于环形等离子体之内,这三种情况下的注波互作用,分别导出了其色散方程;并对色散方程直接进行了数值求解;求得了系统的截止频率、工作频率和波增长率,讨论了有关参数对它们的影响。     

An Experimental Study on Cyclotron–Cherenkov Radiation

We searched numerically dielectric-loaded cylindrical waveguide configurations with an injected electron beam in which the growth rate of the cyclotron-Cherenkov instability surpassed that of the Cherenkov instability, and found such a configuration. This configuration consists of a metallic core and an outer metallic cylinder with a dielectric liner on the inner surface. In order to investigate experimentally radiation due to the cyclotron-Cherenkov instability, we designed and assembled an experimental device using the computational results. We studied beam propagation in the dielectric-loaded coaxial waveguide and microwave radiation due to the cyclotron-Cherenkov instability and the Cherenkov instability.     

A Cherenkov source for freely-propagating terahertz beams

Using a unique cylindrical optical arrangement, the authors have coupled out a Cherenkov electromagnetic shock wave from the confining dielectric substrate and have used this shock wave as a source to produce freely propagating terahertz pulses. The shock wave is initially generated by a surface-dipole distribution propagating faster than the phase velocity in the underlying dielectric substrate     

Analysis and Calculations on Dispersion Relation and Coupling Resistance of Periodic Plasma-Cavities

The plasma tensor dielectric permittivity and electromagnetic field accurate expressions in the external axial magnetic field are obtained from the Maxwell’s equations and the double component plasma particle linear movement equations. Further, the flux of energy inside the plasma-cavity drift channel is presented. Based on them, some of the property of cavity passband dispersion and coupling resistance of plasma-filled coupled-cavities slow wave structure in different plasma density and magnetic field conditions is analyzed according to the numerical calculation.     

耦合腔行波管大信号注波互作用研究与设计

行波管中注波互作用的特点是电子的速度调制、群聚及其与高频场的能量转换等过程沿整个慢波结构连续且同时进行,这是行波管可以在很宽频带内得到大输出功率的原因。在研究冷腔特性的基础上,使用三维PIC粒子模拟软件定量分析了耦合腔行波管的大信号注波互作用过程,完成了X波段连续波行波管的设计。设计参数:工作频率7.18.5GHz,带宽18%,最大输出功率3kW。     

Design and Experimental Demonstration of Cherenkov Radiation Source Based on Metallic Photonic Crystal Slow Wave Structure

This paper presents a kind of Cherenkov radiation source based on metallic photonic crystal (MPC) slow-wave structure (SWS) cavity. The Cherenkov source designed by linear theory works at 34.7 GHz when the cathode voltage is 550 kV. The three-dimensional particle-in-cell (PIC) simulation of the SWS shows the operating frequency of 35.56 GHz with a single TM₀₁ mode is basically consistent with the theoretically one under the same parameters. An experiment was implemented to testify the results of theory and PIC simulation. The experimental system includes a cathode emitting unit, the SWS, a magnetic system, an output antenna, and detectors. Experimental results show that the operating frequency through detecting the retarded time of wave propagation in waveguides is around 35.5 GHz with a single TM₀₁ mode and an output power reaching 54 MW. It indicates that the MPC structure can reduce mode competition. The purpose of the paper is to show in theory and in preliminary experiment that a SWS with PBG can produce microwaves in TM₀₁ mode. But it still provides a good experimental and theoretical foundation for designing high-power microwave devices.     

Analysis of the properties of slow-wave structures based on coaxial resonators coupled by two arc-shaped waveguides

The dispersion and the coupling resistance of spatial harmonics of slow-wave structures formed by a chain of coaxial resonators coupled by arc-shaped waveguides are theoretically analyzed. A 3D vector boundary value problem is solved in the rigorous electromagnetic formulation with the use of projection methods. The 2D problems of excitation of a coaxial resonator are considered and amplitudes of excited waves are determined and used for solution of the 3D problem of the junction of arc-shaped waveguides and a coaxial resonator. The dispersion equation for the considered slow-wave structure is obtained. The results of calculation of the dispersion and the coupling resistance for different numbers and different configurations of coupling apertures are analyzed.