Weibel型不稳定性增益机理的相位条件和宽频带慢波迴旅放大器

正 (一)引言 电子迴旋脉塞(Gyrotron)作为一类新型的快波器件,可在毫米、亚毫米波段有效地产生高功率相干辐射,标志着微波电子学的一大突破。 Gyrotron与普通微波管在作用机理上有很大的区别。它采用光滑波导或过模谐振腔作为高频结构,取代了传统的慢波电路或谐振腔。Gyrotron为快波型器件,而微波管一般为慢波型器件。不久前,有人提出利用慢波互作用的变态迴旋脉塞器件即weibel型器件。Gyrotron快波型器件的作用机理来自迴旋脉塞不稳定性,而Weibel型慢波器件的     

迴旋佩尼管束波互作用的理论和模拟

本文从电子的相对论运动方程和能量方程出发,详细分析了迴旋佩尼管内的束波互作用,提出了适用于任意TEmn模和任何次迴旋谐波工作的大信号理论。计算机模拟表明,这种器件具有电子效率高、工作磁场低的突出优点。从而开拓了毫米波迴旋脉塞器件的更广泛的应用前景。     

矩形介质镜象波导的单模带宽

本文分析了矩形介质镜象波导特征方程的性质,得到以下结论:(1)E_(11)~y模是唯一的没有截止频率的模。因此,无论几何尺寸α、b及介质的相对介电常数∈_r,取何值,最低模式只能是E_(11)~y模;(2)E_(12)~x模的截止频率可由,式直接确定;(3)单模区相应的归一化波导高度B必小于1。大量的数值计算均与上述结论一致。     

迴旋行波管中波型耦合系数的计算

本文用磁流体力学方程组推导了纵向磁化迴旋漂移相对论电子束的介电张量,然后将迴旋行波管作为部分填充各向异性介质的波导,计算了各本征模之间的耦合系数。计算结果表明,只有角向变化次数相同的模才发生耦合。本文对工作在非基模的迴旋脉塞器件估计模式纯度有一定实用价值。     

在迴旋管谐振迴路中利用缓变椭圆截面过渡段来抑制杂模的探讨

在迴旋管中圆截面谐振腔与圆环电子束相互作用是最合理的。但在这种腔中有与主模谐振频率极接近的杂模存在,本文探讨在相互作用区仍用圆截面谐振腔,而在互作用区外加进一段特殊设计的缓变椭圆过渡段用来抑制杂模的可能性。我们这样设计,其杂模场强能够延伸进过渡段而主模场强则不行;再在过渡段中加载,使其起到抑制杂模而保存主模(cTE0n和sTE1n)的作用。     

H02模二次谐波单腔迴旋脉塞的研究

设计在8mm波段的H_(02)模二次谐波工作的单腔迴旋脉塞(gyromonotron)已获初步结果,其峰值输出功率约30kW。文中比较详细地分析了二次谐波工作的物理机理,强调指出互作用的物理实质是拉莫尔半径效应,同时讨论了模式控制问题。由于在设计中从电动力学和电子学两方面采取了模式控制措施,因此主模工作较稳定。最后还展望了二次谐波工作的迴旋脉塞的前景。     

大迴旋半径电子迴旋脉塞的线性理论

本文利用扰动方法,详细研究了大迴旋半径(电子绕波导轴旋转)电子迴旋脉塞。导出了电子的扰动运动。求得了脉塞(包括迴旋管和迴旋潘尼管)的色散方程,并进行了讨论。     

回旋管简介

迴旋管(Gyrotron)作为一种大功率毫米波器件,在国内外受到普遍重视。本刊采访了有关研究单位,就迴旋管的工作原理、目前发展状况及类型、应用前景、研制中可能遇到的科学技术问题等提出了一系列问题,被采访的同志作了热情的解答。现摘要报导如下: 问:请谈一下迴旋管的发展历史及其工作原理,好吗? 答:迴旋管亦称电子迴旋脉泽(The Electron Cyclotron Maser),是指具有较大的横向能量的迴旋电子注在     

电磁波泵浦的自由电子激光器

本文研究了电磁波泵浦的自由电子激光器。从跃变磁场结构出来的大半径迴旋环形电子束通过圆柱形波导与圆柱形波导的TE11模入射电磁波相作用。利用电子束的弗拉索夫分布函数理论和三维波导模的波动方程求得在康普顿区域中的散射波色散关系。通过数值分析,讨论了轴向引导磁场,电子束能量,电子迴旋比和电子束环的径向位置等与散射波频率和增长率的关系。     

脉冲磁控管的阴极问题

在脉冲磁控管中,阳极电流可以用两个不同的公式表示。一是属于具体管型的,包含电磁参数和管的几何尺寸,它描述阳极如何从切向迴旋的电子云中提取电子。另一个只与阴极的热发射、回轰系数和次级发射系数有关,它描述阴极向迴旋电子云供应电子的一般方式。二者有紧密的联系,但又是不同的物理过程。我们将这两个公式和互作用空间中的电子云运动结合起来,便能更好地了解磁控管的工作机制。 为了使磁控管能稳定工作,就要使预振电压低于门槛电压,并且使空间电荷振荡的模式与谐振腔上高频振荡的模同步。在起振之后,阳极电流应近似地由次级发射供应,而回轰电流则近似地由热发射供应。此条件能保证得到较好的工作状态。     

The research of resonant cavity with elliptical cross-section at moderate eccentricity in gyrotron

In this paper, the method of calculating cut-off frequencies of TE modes in elliptical waveguide is given. From the calculations, it is demonstrated that the gyrotron utilizing a cavity with elliptical cross-section of moderate eccentricity has the following characteristics: (a) a large volume cavity can be used; (b) the density of modes which can oscillate is low; (c) it is allowable to use an electron beam with a large diameter; (d) it is possible to use a cavity mode with low azimuthal number.     

大半径同轴谐振腔太赫兹回旋管研究

 为了发展大功率太赫兹辐射源,本文对大半径同轴谐振腔回旋管进行了理论和数值模拟研究,理论计算结果表明在同轴谐振腔中其角向对称的TE_0n模式的截止频率与n近似成正比关系,与内外导体之间的距离近似成反比关系.根据上述特点作者设计了一只大半径同轴腔0.3THz、TE₀₄模回旋管,数值计算和粒子模拟结果表明:大半径同轴谐振腔太赫兹回旋管与空心波导谐振腔回旋管相比具有很多优点:腔体尺寸相对较大,工作电流可以大幅度提高;其对称的TE_0n模式与非对称的TE_mn模式的间隔较大,有利于克服模式竞争.     

Mode competition,suppression, and efficiency enhancement in overmoded gyrotron oscillators

Gyrotron oscillators are of great interest as sources of high power mm wave radiation for electron cyclotron resonance heating and current drive in magnetic fusion research devices. Gyrotrons capable of efficiently generating cw power ? 1 megawatt will be required in future magnetic fusion studies. However, as gyrotron power approaches the megawatt level, a very large, overmoded cavity must be employed in order to keep ohmic power losses in the cavity at an acceptable level, and the problem of mode overpopulation becomes severe. Also, it becomes increasingly important to optimize gyrotron efficiency for a number of important reasons including minimizing the problem of collecting the electron beam energy. In the present paper, a detailed experimental and theoretical study of mode competition and mode locking in an overmoded gyrotron is presented. Efficiency enhancement (to 60%) and high peak power (430 kW) were achieved in the TE_2,4,1 mode using magnetostatic profiling in the cavity. With selective mode suppression, peak power of 475 kW was generated in the TE_0,4,1 mode.     

Cylindrical Cavity with Distributed Longitudinal Corrugations for Second-Harmonic Gyrotrons

Metallic cavity with distributed longitudinal corrugations is proposed and studied for the use in a subterahertz second-harmonic gyrotron. The corrugated conducting walls are treated as a homogeneous surface with effective (averaged) anisotropic impedance. The theoretical study incorporates both single-mode and coupled-mode approaches. It is shown that the distributed longitudinal corrugations provide several-fold increase in the Q-value of the operating mode with respect to that of the fundamental competing mode at a reasonable level of ohmic losses and mode conversion in the gyrotron cavity.     

A mode-matching technique for mode coupling in a gyrotron cavity

The mode-matching technique (MMT) is used to compute the electromagnetic fields, stored energy, and input admittances of a gyrotron cavity coupled to one or more waveguides. The method is based on matching the cavity and waveguide eigenmodes across the cavity apertures and accommodates cavity walls of finite conductivity. The MMT is used in the gyrotron problem because fields in and near the aperture must be computed accurately, and because the eigenmode decomposition is advantageous for inclusion of an electron beam. Irrotational modes are part of the complete set of orthogonal vectors required to expand an H-field in an open cavity, but were excluded in most gyrotron literature; here, this is corrected. The MMT is numerically implemented for cavities of rectangular and circular cross section. Coupling between different modes in a gyrotron cavity through external and ohmic losses is demonstrated. A coupled (complex) cavity gyrotron design is analyzed using MMT. The energy and modal spectra of the cavity are computed, demonstrating the mode selective properties of the design     

Design of a Quasi-Optical System Converting the TE06 Output Mode of a Gyrotron into a Gaussian-Like Beam

Gaussian optics can be used to design a quasi-optical system converting the TE₀₆ mode output (f=388 GHz) of a submillimeter wave gyrotron into a well-collimated, linearly-polarized free-space beam with a circular cross-section. A quasi-optical antenna produces a main beam with an elliptical cross-section, which is then converted by two mirrors into a well-collimated beam with a circular cross-section.     

Multimode Oscillation and Mode Competition in High-Frequency Gyrotrons

Stable operation in a single mode is an important goal of high-power gyrotrons. Both multimoding and switching into unwanted modes can lead to lower efficiency and undesirable heating of components not designed to accommodate parasitic modes. We have extensively studied mode behavior in a pulsed 100-kW, 140-GHz gyrotron using a variety of mixing techniques. As a result, a number of multimoding regions have been identified. Two possible explanations are presented. If the ratio of beam thickness to cavity radius is relatively large, different parts of the beam can excite different modes. Secondly, it can be shown theoretically that, under certain conditions, the presence of one mode can enlarge the excitation region of a neighboring, parasitic mode by favorably prebunching the beam. Experimental evidence strongly supports this latter interpretation. To our knowledge, this is the first use of mixing techniques in conjunction with the study of gyrotron operation. These diagnostic methods are important becanse they can conclusively identify the presence of parasitic modes, even when these modes are weakly excited.     

Numerical Simulation and Analysis of a New Type of Complex Cavity for Gyrotron Applications

A new type of complex cavity structure is used to improve the selectivity of modes in gyrotron resonant cavity with a rational position of inter-cavity wall and the shape of coupling holes between inter- and outer-cavities. The resonant characteristics of the complex cavity operating in TE₀₂₁/TE₀₃₁ mode at Ka frequency band are simulated and analyzed with Ansoft HFSS code, which shows that mode competition can effectively be alleviated with the cavity structure and it may be useful to the formation of clustered-cavity for extending interaction frequency bandwidth.     

A cavity with reduced mode conversion for gyrotrons

Mode conversion at discontinuities of an ordinary gyrotron cavity is examined. It is shown how the production of unwanted spurious modes can be reduced substantially by introducing smooth transition regions between the individual parts of the cavity. The cavity of the 140 GHz KfK gyrotron operating in the TE_10,4 mode is used as an example. Cavity and adjacent tapered output waveguide are optimized as a single unit.     

Coaxial cavities with corrugated inner conductor for gyrotrons

This paper investigates coaxial gyrotron cavities with longitudinal slots on the inner conductor as a means to reduce the number of possible competing modes. In the analytic theory the corrugated surface is treated as a homogeneous impedance surface (“impedance corrugation”) to obtain simple formulas for the characteristic equation of the eigenmodes, for the electromagnetic fields and the wall losses. The developed model applies if the number of slots is sufficiently high (cutoff wavelength much larger than the corruption period). The characteristic equation in terms of the ratio C of the outer wall radius to the inner conductor radius is solved numerically to determine a range of eigenvalues and C where the eigenvalue curves are monotonically decreasing. In such a region a cavity having its inner conductor downtapered (radius decreasing toward the cavity output) can be used to reduce the diffractive quality factors of several modes, leaving the working mode undisturbed and without favoring other modes. In addition the electromagnetic field profiles are investigated, and in particular it is shown that for certain cavity parameters a mode could have its energy concentrated close to the inner conductor. As a check on the validity of the theoretical approximations, simulations with the MAFIA code are carried out. These give good agreement with the results of the analytic equations