Steady-State Spatial Solitons in Low-Amplitude Regime in Biased Photorefractive-Photovoltaic Crystals

A theory of the space-charge field is improved in biased photorefractive-phorovoltaic crystals. Steady-state spatial solitons are obtained in the low-amplitude regime in biased photorefractive-photovoltaic crystals. When photovoltaic effect is neglected, these solitons are screening solitons, and their space-charge field is the space-charge field of screening solitons. When the external field is absent, these solitons are photovoltaic solitons for the closed or the open circuit and we also predict that gray solitons exist in photorefractive-photovoltaic crystals, and their space-charge field is the space-charge field of photovoltaic solitons.     

Space-charge limiting current in spherical cathode diodes

The results of the investigation on the space-charge limiting current for a spherical-cathode diode in the nonrelativistic situation are presented in this paper,The results show that the current enhancement factor equals the square of E-field enhancement factor on the cathode surface,The generated space-charge limiting current is deduced.In the case of a pin-shaped-cathode diode,the space-charge limiting current is also obtained.Indicating that the current is independent of the geometric paramters of the diode.Analyses of the shielding effects and the conditions for generation of the uniform space-charge limiting beam show that ,for pin-arrayed cathodes,the distance between pins should be in the range from 1.2D to 1.5D.where D is the distance between the two electrodes.     

基于伽辽金级数的空间电荷场计算模型

利用局部伽辽金矩量法,建立了电子注空间电荷场的2.5维计算模型. 将空间电荷场在径向展开为各个模式的叠加,利用伽辽金级数表示,通过求解其系数方程组, 最终求得空间电荷场.利用本文的模型,计算分析了电子注空间电荷场的特性, 并研究了模型中仿真参量对空间电荷场计算结果的影响.本文的空间电荷场计算模型利用粒子模拟基本方法, 可以应用到速调管注波互作用计算模型中.     

静电加速管中强流空间电荷效应的研究

 对一种工业用大功率电子加速器(450kW)的加速管中的空间电荷效应作了5点假设，建立了物理模型。对模型的束内外径向电位分布、空间电荷对轴上电位的影响，以及空间电荷力对束流传输的影响等进行了理论分析，得到了束内径向电位分布。结果表明：束流内部径向电位沿径向均呈抛物线变化，并在轴上达到最小值；而空间电荷产生的束内电场与半径呈线性变化；空间电荷不仅会引起轴上电位的跌落，而且对束流有发散作用，特别是在电子速度较低时更为明显。在考虑了空间电荷效应后，强流静电加速管的电场设计关键在加速管的前端，与弱流加速管相比，强流加速管的电场变化要大得多。     

Higher-order space-charge field effects on the self-deflection of photovoltaic dark spatial solitons

We investigate theoretically the effects of higher-order space-charge field on the self-deflection of photovoltaic dark spatial solitons by numerical method under steady-state conditions. The expression for an induced space-charge electric field, including higher-order space-charge field terms is obtained. Numerical results indicate that photovoltaic dark solitons possess self-deflection process during propagation, and the solitons always bend in the direction of the c-axis of the crystal. The self-deflection of dark solitons can experience considerable increase especially in the regime of high photovoltaic field strengths. Relevant examples are provided.     

四种磁绝缘传输线的横向空间电荷流

 根据电磁场基本理论及电子运动守恒方程，导出平板、圆柱、圆锥和圆盘这4种常用传输线的横向空间电荷流的数值模型和磁绝缘临界条件。通过数值模拟得到:传输线的电压越高，无磁场的横向空间电荷流越大，但是磁缘性能却越显著；若分别增大圆柱、圆锥的几何结构因子，既有助于减小它们的无磁场横向空间电荷流又有助于增强它们的磁绝缘性能；对于圆锥，若电极夹角较大，内电极的极角较小，则对减小无磁场空间电荷流和增强磁绝缘性也有一定好处。     

Nonlinear behavior of localized space-charge waves in space-charge dominated electron beams

We present experimental observations of the abnormal growth of localized nonlinear space-charge waves in space-charge dominated electron beams passing through a resistive channel. The energy width of the space-charge waves is measured on both ends of the channel. Previous experiments had shown that, for small initial perturbations, the energy width of the slow waves increases, while the energy width of the fast waves decreases, in agreement with linear theory. We report that in the nonlinear regime (large initial perturbations), the energy width of the fast wave increases, which is unexpected, and, to the best of our knowledge, no theory exists that would predict this phenomenon.     

Investigation into MIS structures based on gradedband-gap hetero-epitaxial HgCdTe grown by molecular-beam epitaxy using photo-emf and conductivity methods

The effect of graded-band-gap layers on the differential resistance of space-charge region in MIS structures based on MBE HgCdTe (x = 0.225) is examined. It is shown that the effect of resistance of the epitaxial-film bulk on the measured capacitance and resistance should be taken into account for correct determination of space-charge region parameters. The presence of near-surface layers with increased Cd contents results in an increase in the resistance of the space-charge region in strong inversion. The product of semiconductor resistance by area as high as 15 Ω⋅cm² is obtained despite suppression of tunnel generation-recombination through deep levels in MIS structures with graded-band-gap layers. This might be due to background photogeneration and diffusion of minority charge carriers. The mechanisms for limitation of the differential resistance of space-charge region at different temperatures are discussed for n-HgCdTe (x = 0.225 and 0.292) and p-HgCdTe (x = 0.225).     

KTa_(1-x)Nb_xO_3:Cu晶体中直流空间电荷场的进一步研究

分别用扩束光和一束写入光对KTa_(1-x)Nb_xO_3:Cu(X=0.32)晶体中的光折变栅进行擦洗,通过不同的擦洗效果,进一步论证了在写入过程中除了形成周期分布的空间电荷场之外,同时还形成了直流空间电荷场.并对直流空间电荷场被擦洗的动态过程进行了详细研究.此外,在写入之前利用一束均匀光照射在外加电场作用下的KTa_(1-x)Nb_xO_3:Cu晶体,研究了直流空间电荷场的形成对衍射信号强度的影响.     

光折变晶体中间段空间电荷场强度特性研究

从Kukhtarev材料方程出发,在单载流子和不假定自由载流子线性复合情况下,推出了中间段非线性空间电荷场的表达式.对其强度特性进行了理论分析.用Ce:KNSBN晶体进行了两波耦合的强度特性实验研究.     

等离子体波在喇曼自由电子激光中的作用

本文用参量放大器模型,分析了喇曼型自由电子激光中等离子体波的作用。结果表明,在忽略电子束初始横向速度的情况下,慢等离子体波与散射波耦合的必要条件为k_wv₂₀>ω_c,即电子的平衡态运动应处于第一组轨道。文中还求出散射波的色散特性和增益公式,以及散射波与等离子体波的相位匹配关系。 关键词：     

稳定化氧化锆的晶界导电模型

晶界空间电荷层在高纯的稳定化ZrO₂的晶界电阻中起着重要作用，以此为基础，提出了一个稳定化ZrO₂的晶界导电模型，根据这个模型分析了Ca,Y和Al的晶界偏聚对稳定化ZrO₂的晶界导电性的影响，并同时分析了被广泛应用的以Bauerle等效电路为基础的晶界电阻测量方法的局限性，以及一些晶界性能表征参量的物理意义及欠妥之处. 关键词：     

Higher-order space-charge field effects on the self-deflection of two-photon bright photovoltaic spatial solitons

We investigate numerically the effects of higher-order space-charge field on the self-deflection of bright photovoltaic spatial solitons in two-photon photovoltaic photorefractive crystals under steady-state conditions. The expression for an induced space-charge electric field, including higher-order space-charge field terms is obtained. The dynamical evolution equation is built in which the effects that arise from these higher-order terms are considered. Numerical results indicate that bright photovoltaic solitons can bend towards both the same direction as the crystal's c-axis and the opposite direction, respectively. Specifically, self-deflection cannot occur for bright photovoltaic solitons if the strength of the photovoltaic field and the intensity of the input beam are appropriately selected. Relevant examples are provided.     

Traveling-wave-tube simulation: The IBC code

An interactive beam-circuit code (IBC) is presented, to run interactively on fast PCs or workstations, for purposes of first-cut design of traveling-wave tubes (TWTs) at small and large amplitudes. The new physics parts are the use of particle-in-cell methods to obtain the space-charge forces, and the following of the electron beam over the full length of the tube. The model is fully nonlinear and one-dimensional, with the transverse space-charge fields approximated by one mode. The slow-wave circuit is modeled by a transmission line. All variables are displayed continuously, such as the velocity displacement of all the particles (phase space), beam charge and current densities, space-charge field, circuit field, voltage and current, circuit power, and the location of the added loss. Some initial runs are presented     

Mode Coupling in a Partially Filled Plasma Waveguide With a Dielectric Liner

The stimulated Raman scattering of a perturbed TM mode in a dielectric loaded partially filled plasma waveguide is considered. The radiation is the result of the scattering of pump electromagnetic wave, which is an EH waveguide mode, off of a space-charge wave. A nonlinear wave equation for a three-wave interaction is used to investigate the coupling of the space-charge and waveguide modes. Dispersion relations for electromagnetic modes are solved numerically to study the frequency characteristics of the interaction of the EH waveguide modes with the space-charge modes. Formulas for the growth rates of the backscattered wave near the electron cyclotron frequency are derived, and the effect of a dielectric liner on the growth rates is investigated. Numerical studies show that the presence of the dielectric liner has an effect on the phase-matching condition and leads to rather larger growth rates close to electron cyclotron resonance.      

The Spectrum of Deep Levels in the InP Schottky Barrier

The energy spectrum of deep levels in the space-charge region of the Schottky barrier of InP field-effect transistors is determined by the method of tunneling spectroscopy. It has been established that for the most part the space-charge region of the Schottky barrier has electron traps with large capture cross sections that control the tunneling current in the Schottky barrier.     

带状电子束的空间电荷场

 利用理论分析和数值计算的方法研究了矩形波导内均匀电流密度的带状电子束模型的空间电荷场,给出了该带状电子束模型的空间电荷场的解析表达式,并研究了空间电荷场随带状电子束的几何参数和物理参数的变化规律。研究表明：在不改变电流密度的前提下,更宽的电子束可以传输更强的束流,而空间电荷场并不随束宽度的增大而增大,但是增加电子束厚度会使空间电荷场显著增强,从而不利于高流强电子束的传输;对于相同电流的带状电子束,保持电子束厚度不变,增大电子束宽度,相应地降低电流密度是降低空间电荷场的一个很好的途径,而保持电子束的宽度不变,增大束厚度,相应地降低电流密度只会使沿着电子束截面宽度方向的电场减小,而沿着电子束截面厚度方向的电场基本不变;对于相同电流和电流密度的带状电子束,更宽、更薄的电子束横截面尺寸能使沿着电子束截面宽度方向的电场降到更低,而沿着电子束截面厚度方向的电场只是略有减小。     

Reduced space-charge fields in near-stoichiometric LiTaO3 for blue, violet, and near-ultraviolet light beams

The wavelength dependence of the space-charge field as induced in near-stoichiometric LiTaO₃ crystals is investigated by measuring the bulk photogalvanic effect and the photoconductivity. LiTaO₃ crystals of composition nearer to stoichiometry exhibit a pronounced reduction of the saturated space-charge field, which results from a larger increase in the photoconductivity relative to the photogalvanic effect. Especially, at near-UV wavelengths, the saturated space-charge field of the order of 0.1 kV/cm reaches a minimum that is two orders of magnitude lower than typical values observed in undoped near-stoichiometric LiNbO₃. Received: 11 July 2002 / Revised version: 2 September 2002 / Published online: 20 December 2002 RID="*" ID="*"Corresponding author. Fax: +41-1/633-1056, E-mail: mojca@fiz.uni-lj.si     

多次聚束的空间电荷波理论

本文采用空间电荷波的观念,讨论了包括电子相互作用的多次聚束问题。所得结果,在电流接近以零为极限时,简化成费恩柏格(E.Feenberg)由运动学观点出发的结果。但是空间电荷效应的包括,显示了多次聚束系统一些不能由运动学方法得到的特徵。本文的分析,可以应用在一系列的微波电子器件上。文中对这方面,也提供了一些具体的方向。     

Relations Between Focusing Power of Space-Charge Lenses and External Electromagnetic Fields

Under different external electromagnetic fields,the electron densities of the electron cloud in a self-sustaining space-charge lens are measured with the radio-frequency method and the energy distributions of the ions produced in ionization are measured with the stopping field method.From them the relations between the focusing power of space-charge lenses and the external electromagnetic fields are determined.The available region of the Lebedev-Morozov formula is discussed.