Penetration of a magnetic field into a thin unclosed ellipsoidal sheath in the presence of a thick-walled conducting spherical sheath

The solution of the problem of magnetic field penetration into a conducting unclosed ellipsoidal sheath in the presence of a conducting thick-walled spherical sheath is reduced to the solution of the integral Fredholm equation of the second kind. The effect of the apex angle of the unclosed ellipsoidal sheath, geometric parameters of the screens, and electrophysical properties of the spherical sheath material on the field attenuation coefficient inside the ellipsoidal sheath is studied numerically.     

Shielding of low-frequency electric fields by a set of shields consisting of a thin unclosed spherical sheath and thin-walled pervious spherical shell

The penetration of low-frequency electric fields through a thin-walled spherical conducting shell in the presence of a thin unclosed spherical perfectly conducting sheath is considered. The problem is solved by the method of pair summational equations with averaged boundary conditions. The effect of the central angle of the unclosed spherical sheath and field source position on the field attenuation inside the closed thin-walled shell is studied numerically for different shell thicknesses and materials.     

Electrostatic problem for a thin, unclosed ellipsoidal shell and disk

The axisymmetric electrostatic problem of a thin, unclosed ellipsoidal shell and disk is solved. The capacitance coefficients are calculated for a representative set of values of the geometrical parameters of the conductors. Zh. Tekh. Fiz. 69, 1–5 (February 1999)     

Distribution characteristic of scattering field for an ellipsoidal target irradiated by an electromagnetic wave from an arbitrary direction

It is of great importance for engineering applications to obtain the expression of scattering field for an ellipsoidal target irradiated by an electromagnetic wave from an arbitrary direction. Literature relevant to this problem is seldom found. In this paper, the scattering field for an ellipsoidal target is presented by utilizing the scale transformation of electromagnetic field and the rotation of coordinate system, with an electromagnetic wave projecting on the target from an arbitrary direction. The obtained result is in good agreement with the solution available from the literature if we consider the scale factors to be unity. Taking a conducting ellipsoidal target for sample, we perform the partial simulations of the ellipsoidal model and a plant leaf model by choosing different scale factors. The obtained results show that the distribution characteristic of scattering field is sensitively affected by the polarization of the incident wave and varies not much with the incident wave angle but changes with the observation point. At some points the scattering energy arrives at its maximum.     

基于行波管螺旋导电面模型的空间电荷场研究

通过分析行波管螺旋导电面模型中的电磁场，给出了色散和耦合阻抗计算公式，并深入研究了非线性理论中的空间电荷降低因子.结果表明，螺旋导电面模型相对理想导电圆筒中的空间电荷降低因子在较高频段变化不大.空间电荷降低因子的变化反映了螺旋线外电磁场对电子注的作用，同样的慢波结构，较高频率的电磁场应有较大的影响.因此，使用螺旋导电面模型在较高频段计算空间电荷降低因子是不合适的. 关键词： 行波管 非线性 螺旋导电面 空间电荷降低因子 色散 耦合阻抗     

Spreading resistance and 1/f noise of embedded ellipsoidal electrodes in a conductor

Results of calculations for the spreading resistance and the resistance fluctuations due to 1/f conductivity fluctuations are presented. The resistor consists of a conducting medium between a small embedded ellipsoidal electrode and a large electrode at a large distance from the small one. The resistance and resistance fluctuations are compared with the simple results for an embedded hemispherical electrode. The results are presented graphically and can be used for ohmic contacts on semiconductors or for embedded ellipsoidal electrodes in an ionic solution.     

非圆截面托卡马克轴对称模的反馈稳定

通过直接解真空区扰动磁面的边值问题,本文解析地研究了非闭合导壳对托卡马克中轴对称MHD模的反馈稳定性。我们取等离子体截面为椭圆,反馈系统由导壳和主动反馈线圈构成。结果表明,两块放在等离子体上下的导体块有很强的稳定作用;电阻壳可用以抑制高频模式,主动反馈线圈可用以稳定低频模式。 关键词：     

Self-consistent nonlinear resonance and hysteresis of a charged microparticle in a RF sheath

A self-consistent model is proposed to study nonlinear phenomena, such as secondary resonance and hysteresis in the vertical oscillations of a charged microparticle in a radio-frequency sheath. The motion of a single microparticle in the sheath is simulated by solving Newton's equation in which various forces acting on the particle are taken into account. The particle charging and the sheath electric field are described by a self-consistent model of the collisional radio-frequency sheath dynamics. It is found that the nonlinearity is related to the particle's charge, the sheath electric field, and the external excitation force, as well as the ion drag force and neutral-gas friction on the particle.     

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利用发射探针诊断了处于扩散等离子体流场中平板两侧的鞘层电势分布并给出鞘层厚度及边界电场。结合Child-Langmuir(CL)定律并利用一维流体模型,分析对比了鞘厚及边界电场。结果显示,上下游的鞘层呈现不对称结构,下游比上游厚,边界电场下游比上游弱,并且下游的预鞘还呈现类似虚阳极的结构。上下游CL鞘的厚度满足线性比例关系,比例系数约为1.2,且实验值与理论值非常接近。上下游CL鞘的边界电场与模型Te/(eλD)比较接近,上游Bohm鞘边界电场的实验结果与过渡区模型 较符合,但下游Bohm鞘的边界电场与现有模型有较大差异。     

磁化等离子体的鞘层结构

采用流体方法数值研究了斜磁场作用下的等离子体鞘层结构.模拟结果显示磁场对鞘层结构有显著的影响,特别是在磁鞘边界附近离子的密度分布产生了明显的变化.分别讨论了离子垂直入射和斜入射两种情况,当离子斜入射进鞘层时,其运动情况要相对复杂一些.在适当的条件下,洛伦兹力的作用使离子在某些区域产生相对聚集,离子密度分布产生波动. 关键词： 鞘层 等离子体 磁场     

Acoustic characteristics of pulse detonation engine with ellipsoidal reflector

Acoustic characteristics of a pulse detonation engine(PDE) with and without an ellipsoidal reflector are numerically and experimentally investigated. A two-dimensional(2 D) non-splitting unstructured triangular mesh Euler solver based on the space-time conservation element and solution element(CE/SE) method is employed to simulate the flow field of a PDE.The numerical results clearly demonstrate the external flow field of the PDE. The effect of an ellipsoidal reflector on the flow field characteristic near the PDE exit is investigated. The formation process of reflected shock wave and reflected jet shock are reported in detail. An acoustic measurement system is established for the PDE acoustic testing. The experimental results show that the ellipsoidal reflector changes the sound waveform and directivity of PDE sound. The reflected shock wave and reflected jet shock result in two more positive pressure peaks in the sound waveform. The ellipsoidal reflector changes the directivity of PDE sound from 20 to 0. It is found that the peak sound pressure level(PSPL) and overall sound pressure level(OASPL) each obtain an increment when the PDE is installed with a reflector. The maximum relative increase ratio of PSPL and OASPL are obtained at the focus point F2, whose values are 6.1% and 6.84% respectively. The results of the duration of the PDE sound indicate that the reflecting and focusing wave generated by the reflector result in the increment of A duration and B duration before and near focus point F2. Results show that the ellipsoidal reflector has a great influence on the acoustic characteristic of PDE sound. The research is helpful for understanding the influence of an ellipsoidal reflector on the formation and propagation process of PDE sound.     

The sheath criterion for a collisional plasma sheath at the presence of external magnetic field

The Bohm sheath criterion is modified for collisional plasma containing Boltzmann electrons and cold fluid ions at the presence of external magnetic field. Based on fluid model, the effects of the strength and the orientation of an external magnetic field on the upper and lower limits of Bohm sheath criterion have been studied by considering the collision frequency between ions and neutrals. The results show that the sheath criterion depends on the orientation and magnitude of magnetic field and the ion flow velocity at the sheath boundary.     

一种基于离轴椭球面的小光程差波面整形系统

为了实现空间中一定距离的近似等光程光束传输,设计了一种包含离轴椭球面反射镜的波面整形系统。基于几何光学与初级像差理论,结合Zemax光学设计软件,分析了椭球面反射镜圆锥系数、离轴量对像面处光程差的影响;设计了平面-椭球面反射镜和双椭球面反射镜2种光学结构的波面整形系统,并比较了2种结构的公差。分析结果表明:平面-椭球面反射系统和双椭球面反射系统均实现了空间中1 m距离的光束传输,且2种结构系统在3 mm物高视场和孔径角为6°条件下,各视场光瞳之间的光程差分别为0.14 mm和0.04 mm,因此,双椭球面反射结构整形效果优于平面-椭球面反射系统,但双椭球面反射结构对公差的敏感度更高。     

Nonlinear properties of a medium with ellipsoidal ferroelectric nanoinclusions

A model describing the dielectric properties of a composite material with ellipsoidal ferroelectric inclusions has been developed. The dependence of the effective permittivity of the composite material on the applied external electric field is determined for different sizes of ferroelectric inclusions. The controllability of the composite material under consideration is evaluated.     

Electrostatic field penetration through a slot on a conducting half-plane

In this study, electrostatic field penetration through a slot on a conducting half-plane is investigated based on the Mellin transform and mode matching. To formulate the field behavior by the slotted half-plane, a slotted conducting wedge with a line charge is considered as an analysis model. A fast convergent series solution is obtained through the application of eigenfunction expansion and residue calculus. Numerical computations of the electrostatic field are conducted to demonstrate the penetration characteristics for the slotted conducting half-plane in terms of the slot dimensions and the position of the line charge. The computed results are also compared with simulated results.     

斜磁场中碰撞等离子体鞘层的玻姆判据

采用双流体模型研究了斜磁场作用下的碰撞等离子体鞘层的玻姆判据,讨论了磁场对鞘层玻姆判据的影响.结果表明:玻姆判据存在上限和下限,磁场强度、角度以及离子进入鞘层的状态都对离子马赫数的取值范围有影响.     

Sagdeev Potential and Sheath Criterion for a Multi‐Component Plasma

A charged sheath between a multi‐component plasma and an absorbing and conducting wall was considered analytically in the framework of a hydrodynamic model. The model accounted for the inertia and pressures of all the plasma components and both wall polarities. An existence criterion for the steady sheath with a monotonous distribution of the electric potential was derived based on analysis of the Sagdeev potential. The model was applied to some special cases of two‐and three‐component plasmas such as a plasma with macroparticles, and electro‐positive and ‐negative plasmas. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

磁场中等离子体鞘层的结构

采用流体力学理论，研究了斜磁场作用下的等离子体鞘层结构.在不同大小及方向的磁场作用下，对鞘层的离子，电子密度分布，离子流速度分布，电势分布和Bohm判据进行了讨 论.结果显示磁场对鞘层的结构有明显的影响.在静电力和洛仑兹力的作用下，离子流作螺旋进动，离子密度分布产生振荡. 关键词： 磁鞘 等离子体 磁场     

A molecular-dynamics study of oscillations of unclosed crystal nanostructures based on bilayer metal films

Behavior of unclosed nanostructures is investigated in the course of their formation from bilayer films of a Ni–Cu system with crystal structure. The investigation is performed on the basis of the molecular dynamics method using a many-body potential of interatomic interaction. It is shown that the edges of an unclosed nanostructure produced from a bilayer metal film can perform free harmonic oscillations. The dependence of the oscillation amplitude of the nanostructure on the size of the initial film is investigated. Optimum geometrical parameters of the initial film are determined in order to form unclosed nanostructures oscillating with maximum amplitude. The results obtained are promising for the development of components for nanodevices of different types and applications.