介质加载回旋行波管小信号分析

 应用分析回旋行波管绝对不稳定性的Briggs-Bers相碰判据与小信号色散方程，结合介质加载波导的冷场分析，数值计算并比较了不同介质加载条件下回旋行波管工作模式的起振电流与寄生模式的起振长度。改变加载介质的特性参数可以增加行波损耗从而显著提高工作模式起振电流，并抑制掉寄生模式的返波振荡。结合介质加载波导冷场分析与回旋行波管小信号色散方程，分析了介质加载条件下回旋行波管小信号增益，计算得出了不同介质加载条件下的回旋行波管的小信号增益带宽曲线。     

Kα波段介质加载回旋行波管小信号分析与设计

应用分析回旋行波管绝对不稳定性的Briggs-Bers相碰判据与小信号色散方程，并结合介质加载波导的冷场分析，通过数值计算比较了不同介质加载条件下回旋行波管工作模式的起振电流与寄生模式的起振长度，通过改变加载介质的特性参数从而增加行波损耗可以显著提高工作模式起振电流，并抑制掉寄生模式的返波振荡.结合介质加载波导冷场分析与回旋行波管小信号色散方程，分析了介质加载条件下回旋行波管小信号增益，给出了不同介质加载条件下的回旋行波管的小信号增益带宽曲线.在对介质回旋行波管自激振荡与小信号增益的综合分析基础上，对Kα     

Kα波段介质加载回旋行波管小信号分析与设计

应用分析回旋行波管绝对不稳定性的Briggs-Bers相碰判据与小信号色散方程,并结合介质加载波导的冷场分析,通过数值计算比较了不同介质加载条件下回旋行波管工作模式的起振电流与寄生模式的起振长度,通过改变加载介质的特性参数从而增加行波损耗可以显著提高工作模式起振电流,并抑制掉寄生模式的返波振荡.结合介质加载波导冷场分析与回旋行波管小信号色散方程,分析了介质加载条件下回旋行波管小信号增益,给出了不同介质加载条件下的回旋行波管的小信号增益带宽曲线.在对介质回旋行波管自激振荡与小信号增益的综合分析基础上,对Kα 关键词： Kα波段介质加载回旋行波管 绝对不稳定性 自激振荡 小信号增益     

W波段回旋行波管绝对不稳定性的分析

 绝对不稳定性是制约回旋行波管性能的主要因素之一。通过回旋行波管色散方程,详细分析了W波段基波回旋行波管绝对不稳定性的形成和特征,提出了采用多段损耗波导来抑制绝对不稳定性的方法。分析表明,绝对不稳定性的起振存在一定阈值,起振电流对电子注参数和电路参数极其敏感,确定起振电流是稳定器件工作的前提条件。通过PIC模拟,给出了采用无损耗波导结构,且工作电流为25 A和10 A条件下的放大器频谱图和功率图,结果表明绝对不稳定性的出现与否主要由工作电流是否超过起振的阈值电流决定,损耗波导是抑制绝对不稳定性的有效手段。     

太赫兹波段Smith-Purcell辐射的介质加载光栅高频特性

提出了一种用于Smith-Purcell效应器件的介质加载光栅慢波结构,通过研究该结构的注-波互作用过程,推导出带电子注的色散方程,并数值求解出波的线性增长率.利用色散方程,结合电磁场传播的边界条件,推导出Smith-Purcell效应振荡器工作所需的起振电流.详细研究了高频结构长度、电子注主要参数和介质相对介电常数对起振电流的影响,并与普通金属光栅结构进行了比较.结果表明:保持其他参数不变时,高频结构长度越短,起振电流越大;保持高频结构参数不变时,起振电流随电子注厚度和注-栅距离的增大而增大,随电子注电压的增大而减小;与金属光栅相比,介质的引入提高了注-波互作用的增长率,有效减小了振荡器的起振电流.理论计算结果与软件CHIPIC的模拟结果比较符合.     

具有分布损耗波导结构的回旋行波放大器绝对不稳定性

 详细推导了具有分布损耗波导结构的回旋行波放大器的色散特性。通过绝对不稳定性振荡出现的条件,给出求解具有损耗波导结构回旋行波管放大器的绝对不稳定性起振电流的数值计算方法。研究结果表明：绝对不稳定性起振电流与损耗波导的集肤深度有关,选择有较大的集肤深度的损耗波导可以提高绝对不稳定性起振电流;绝对不稳定性起振电流同时也与工作磁场偏离饱和磁场的程度以及电子束的纵横速度比有关;通过设计具有分布损耗波导结构的注-波互作用电路,以及工作磁场、电子束的纵横速度比,可以在兼顾带宽、效率的条件下,保证回旋行波管放大器稳定工作。     

基于损耗介质加载波导的回旋行波管放大器的互作用分析

损耗介质波导对提高回旋行波管放大器的稳定性等性能具有积极的作用.本文基于损耗介质波导中工作模式的场表达式,推导出电子回旋脉塞互作用线性理论.通过系统的数值计算发现损耗介质波导与光滑金属圆波导中的工作模式从场型分布和色散关系上都具有一一对应关系;通过Laplace变换,利用互作用线性理论计算工作模式的起振场型和阈值,并研究互作用系统磁场、电流和介质层对放大特性的影响.这些研究成果对促进损耗介质在回旋行波管放大器中的运用和高稳定性回旋行波管放大器的发展具有积极的作用.     

分布损耗对回旋行波放大器稳定性的影响

基于电磁模式的色散方程和回旋管非线性理论,研究了损耗层厚度对回旋行波放大器注-波互作用的影响.结果表明,合理选择损耗层电导率和厚度能够让期待的工作模式TE₀₁衰减较小,而对应的竞争模式TE₂₁因损耗很大而更难以起振,随厚度的增加,放大带宽从两边向中间收缩变窄,频带中间部分的输出功率会上升,曲线更加平坦,从而达到改善互作用稳定性的目的. 关键词： 回旋行波放大器 起振长度 起振频率 饱和功率     

回旋行波放大器输出端反射对其稳定性的影响

 基于回旋行波放大器的线性理论和反射边界条件,建立了渐变输出端存在反射时回旋行波放大器模型,分析了TE₀₁圆电模基波回旋行波放大器输出端反射对其增益、返波起振长度、返波起振电流和返波起振频率的影响。结果表明,随着反射增强,线性增益降低,返波起振长度和起振电流减小,返波起振频率的变化较小;反射增强将在一定程度内影响放大器的稳定性。     

分布损耗加载回旋行波管多模稳态注波互作用理论与比较证实

基于目前国际上实验研究的均匀介质加载和周期介质加载结构,建立了一种分布式损耗加载回旋行波管(gyro-TWT)多模稳态注波互作用理论.利用这一理论,以TE01模式基波gyro-TWT注波互作用为例,将Ka和W波段的理论结果与实验和软件仿真进行比较,以证实理论的合理性.     

Geometrical Effects on the Performance of Coaxial-Waveguide Gyrotron Traveling-Wave Amplifiers

This theoretical investigation examines the feasibility of improving the stability of the coaxial-waveguide gyrotron traveling-wave tube (gyro-TWT) by selecting the geometrical parameter C, i.e., the ratio of the outer radius to the inner radius. The effects of the geometrical parameter C on the start-oscillation currents of oscillation modes are analyzed to determine the optimum operating conditions. Simulation results indicate that the coaxial gyro-TWT with distributed wall losses can be stably operated at a higher beam current by optimizing C. Additionally, the saturated behaviors of the operating TE₀₁ mode are evaluated for several C values to investigate the geometrical effects on the amplification of the coaxial gyro-TWT. Moreover, performance of the fundamental harmonic coaxial gyro-TWT achieved with the optimized C value is predicted under stable operating conditions.     

Periodicity-suppressing effect of periodic lossy-dielectric-loaded cylindrical waveguide

Periodic dielectric-loaded waveguide is one of the diaphragmatic waveguides.For the excellent mode-selective propagation ability,it is of value for applications in gyrotron-traveling-wave amplifiers(gyro-TWT),accelerators,and other microwave propagation systems.This paper focuses on studying the application of the strong lossy-dielectricloaded periodic waveguide in millimeter-wave gyro-TWT.It is revealed that due to the lossy property of the dielectric,the energy in the dielectric slots is absorbed effectively and the high order Bloch harmonics induced by the periodicity of the structure are suppressed,which changes the discrete spectrum under lossless condition into a continuous one.As a result,the periodicity of the system is severely suppressed and a mode in the hollow region could be approximated by a fast wave mode in an empty waveguide.These results bring specific guidance for the applications of the lossy dielectric-loaded waveguide in gyro-TWTs and other devices.     

W波段TE02模式回旋行波管带宽输入耦合器设计

输入耦合器是回旋行波管的重要组成部分之一,其作用是将矩形波导TE₁₀模式的信号,通过模式变换结构转换为回旋放大器件中的模式,输入耦合器性能的优劣直接影响了回旋管整管的带宽等性能。通过对W波段TE₀₂模式回旋行波管的输入耦合器进行理论分析,指出影响主模传输损耗的一个因素是杂模的崛起使主模的传输系数降低,利用仿真软件进行仿真,通过优化耦合孔的尺寸,抑制杂模的产生,将损耗从3.9 dB降低到了0.8 dB。根据优化尺寸加工,实际测试,得到3.0 dB带宽7.9 GHz的输入耦合器,与设计符合较好。     

140-GHz gyrotron experiments based on a confocal cavity

We have designed and experimentally demonstrated the operation of a novel quasioptical gyrotron oscillator based on an overmoded confocal waveguide cavity. This cavity effectively suppresses undesired modes, and therefore has extremely low mode density. Stable single-mode, single-frequency operation was achieved in the TE₀₆ mode at 136 GHz. A peak RF output power of 66 kW, corresponding to an efficiency of 18%, was measured. By varying the cavity magnetic field, high-power generation was observed at 136 GHz in the TE₀₆ mode and at 114 GHz in the TE₀₅ mode. These frequencies correspond to the high Q modes of the confocal resonator. The low Q modes were either weak or not observed. In this paper, we will review the design procedure for this cavity and present experimental data verifying its effectiveness in reducing the number of modes that can be excited. The confocal waveguide could also be used in high-power, gyro-TWT amplifiers to provide greater operating stability and bandwidth, especially in an overmoded waveguide structure     

Stable 1 MW, third-harmonic gyro-TWT amplifier

The concept that the relatively weak harmonic gyro-TWT interactions allow high values of electron beam current for stable operation has been extended to design two extremely high power, 140 GHz, third-harmonic TE₃₁ gyro-TWT amplifiers. One device is driven by an axis-encircling electron beam from a cusp gun and the other employs a magnetron injection gun (MIG). These devices are predicted by a self-consistent nonlinear numerical simulation code to yield, respectively, output powers of 775 kW and 937 kW with 15.5% and 18.7% efficiency, saturated gains of 27 dB and 30 dB, and saturated bandwidths of % and 6.5%. The stability of the amplifiers is ensured by limiting the length of the interaction section(s) to the shortest starting oscillation length as determined by linear theory. The cylindrical waveguide circuits of both amplifiers have been sliced to suppress modes without a threefold azimuthal symmetry. The amplifier utilizing a MIG yields superior performance because the dominant competing interaction is minimized for the choice of the beam's guiding center radius. The advantages as well as limitations of this approach for high power microwave generation are also addressed     

Effects of Beam and Magnetic Field Parameters on Highly Competing TE01 and TE21 Modes of Vane Loaded Gyro-TWT

In this paper, the dispersion relation for a vane-loaded cylindrical waveguide, considering the azimuthal harmonic effects arising from the azimuthal periodicity of the vanes, excited in transverse electric (TE) modes and the gain for a gyro-TWT have been presented. The effects of beam and magnetic field parameters on two highly competing modes have been studied.     

Large-signal theory of gyro traveling wave tubes at cyclotronharmonics

A nonlinear theory of gyrotron traveling wave tubes (gyro-TWTs) at cyclotron harmonics has been developed taking into account the electron velocity spread and the possibility of operating with significant Doppler frequency up-shift (CARM operation). It is shown that the orbital efficiency of the relativistic gyro-TWT operating at the second cyclotron harmonic with large frequency up-conversion may exceed 60%. It is also shown that the influence of the axial inhomogeneity of the wave field on the relation between amplitudes of electric and magnetic fields of the wave causes small changes in the efficiency of gyro-TWTs. The results obtained demonstrate the sensitivity of the harmonic gyro-TWT efficiency with respect to electron velocity spread at different axial wave numbers. The expressions for the gain are derived and discussed,