Analysis and optimization of blocks in high-frequency sections of linear accelerators and deflectors of charged particles using an equivalent circuit

Analysis and optimization of blocks in high-frequency sections of linear accelerators and defectors of accelerated particles is performed using an equivalent circuit. This circuit correctly simulates the lowest accelerating mode as well as the first dipole mode of the E-type for various structures consisting of coupled cells. Analytic expressions are derived for parameters of individual cells of sections for which traveling waves with a preset form of oscillations propagate at a given frequency; optimization of the parameters of the input and output wave-type transformers is carried out. Simple analytic expressions are considered for calculating the complex reflection coefficient of a section in a certain cross section of the lead-in waveguide. The sections may contain identical cells as well as different cells.     

五层MOS光波导TE模光学特性的简化分析

应用一种简化的方法对五层MOS光波导的光学特性进行了分析,给出了TE模传播常数和吸收损耗系数的近似计算公式,并结合计算结果检验了本方法及公式的精度,为实现波导中TE_0模低损耗单模传输,讨论了某些波导参量的选择.     

天线罩电厚度与材料电参数六端口测量系统设计

 介绍了一个可用于天线罩电厚度与介质材料介电常数测量的六端口反射计系统,它由对称波导五端口结与定向耦合器组成,其关键部件波导五端口结用HFSS软件仿真与设计。介绍了天线罩相对电厚度复反射系数的测量方法。用该系统对滑动短路器复反射系数进行了测量,测量结果表明,系统工作稳定,测试精度高。利用短路波导法测量了材料介电常数和损耗角正切,测量结果显示：介电常数测量的精度和稳定度较高,损耗正切的测量误差较大。     

Computation of the Reflection Coefficient of a Triangular Semiconductor Prism in a Rectangular Waveguide

In this paper we present a method to solve Maxwell's equations that enables to compute waveguide structure containing a semiconductor triangular prism. The numerical study has showed that the triangular prism in the waveguide has a wider frequency band in comparison with a square rod under equal conditions. The reflection coefficient dependencies on frequency, prism size and its permittivity have been computed. The algorithm and computer programme have been tested and compared with the numerical results and experimental data of the paper [1] with good agreement.     

Quantum and semiclassical studies on photodetachment cross sections of H~- in a harmonic potential

The photodetachment cross section of H~- in a linear harmonic oscillator potential is investigated. This system provides a rare example that can be studied analytically by both quantum and semiclassical methods with some approximations. The formulas of the cross section for different laser polarization directions are explicitly derived by both the traditional quantum approach and closed-orbit theory. In the traditional quantum approach, we calculate the cross sections in coordinate representation and momentum representation, and get the same formulas. We compare the quantum formulas with closed-orbit theory formulas, and find that when the detachment electron energy is larger than3/2hω, where ω is the frequency of the oscillator potential, the quantum results are shown to be in good agreement with the semiclassical results.     

稀土掺杂固体发光材料的光谱分析

光谱分析是评价稀土发光材料光谱性质的主要依据,Judd-Ofelt(J-O)理论是光谱分析的基础。详述了采用J-O模型拟合三个强度参量和估算一些重要辐射参量的操作细节,讨论了相关公式的合理应用,总结了计算中误差的主要来源,并推荐了一种通过低温实验获得较可靠光谱参量的途径。建议采用透射光谱数据计算实验跃迁振子强度,吸收系数和吸收截面的计算应该扣除光反射、散射和基质本身吸收的影响,平均波数和平均波长的取值须考虑线形因子。并建议通过发射光谱的实测线形计算各波长的发射截面。由于J-O模型涉及许多近似和假设,计算结果误差较大,可能导致结果不可靠。通过分析指出,采用低温下测得的能级寿命和荧光分支比进行相关参量的估算可获得较可靠、较有意义的结果。     

浅水近距离测量声场的干涉结构分析

为指导浅水中水平距离在十倍水深范围内进行的近距离声学测量工作,选取对软底浅水声场产生主要贡献的直达声线和一次水面反射声线,经过合理的近似处理,以射线解析方式给出了中低频信号声场干涉结构的表达式,并将表达式由单频信号推广到宽带信号和线性调频等信号形式。所得到的解析关系式定量给出了浅水中声场干涉结构与信号频率、信号带宽、设备布放深度和水平距离等参数的关系,由此进一步得到浅水条件下中近距离干涉声场的一些特性和规律。通过数值模拟和实际试验数据对上述关系式所进行的检验表明:在浅水的常规测量试验条件下,这些关系式可以较为准确地反映近距离干涉声场的起伏特征,由关系式推论得到的声场特性和规律也得到了初步验证。     

Asymptotic Formulas for the Eigenvalues of Hybrid Modes in Optical Fibers with Step-Like Profiles of the Refractive Index

Based on the approximations for the cylindrical-function ratios in the characteristic equation, we obtain asymptotic formulas for the eigenvalues of hybrid modes. The obtained expressions allow one to take into account variations in any waveguide parameter and to calculate the difference of the eigenvalues of modes belonging to the same mode group.     

Three-dimensional vectorial analysis of waveguide structures with the method of lines

The method of lines (MoL) a special eigenmode algorithm has been proven as an efficient tool for the analysis of waveguide structures in optics and microwaves. The electric and magnetic fields in the cross-section and their derivatives with respect to the cross-section coordinates are discretized with finite differences (FD) while analytic expressions are used in the direction of propagation. The numerical effort for analyzing three-dimensional structures with a two-dimensional discretization can be very high, particularly if vectorial characteristics have to be taken into account. In this paper we introduce a reduction of the eigenmode system to keep the effort moderate. Only a certain number of eigenmodes is determined with the Arnoldi algorithm. We will show then how the electric field distribution of the eigenmodes can be computed from the magnetic field and vice versa. To match the fields at the interfaces we introduce left eigenvectors which are the inverse of the field distributions. The formulas were applied to the analysis of a polarization converter consisting of a periodical perturbation of a waveguide structure. A rotation angle greater than 80° was determined.     

Approximate Transmission Coefficients in Heavy Ion Fusion

In this paper, we revisit the one-dimensional tunneling problem. We consider different approximations for the transmission through the Coulomb barrier in heavy ion collisions at near-barrier energies. First, we discuss approximations of the barrier shape by functional forms where the transmission coefficient is known analytically. Then, we consider Kemble’s approximation for the transmission coefficient. We show how this approximation can be extended to above-barrier energies by performing the analytical continuation of the radial coordinate to the complex plane. We investigate the validity of the different approximations considered in this paper by comparing their predictions for transmission coefficients and cross sections of three heavy ion systems with the corresponding quantum mechanical results.     

Analytic study on acoustic interference pattern in shallow water

Analytic formulas for acoustic interference patterns in shallow water are derived by ray method. Which can be used to guide acoustic measurements with limited horizontal distances. Some necessary approximations are taken for a concise expression. The analytic formulas represent the quantitative relationships between the interference-pattern and the signal frequency, bandwidth, depth of source and horizontal distance. Monofrequent signals, complicated signals and frequency-modulated signals are all studied. Several inferences are also deduced from the formulas. Both numerical simulations and experiment data are presented to prove that these formulas and their inferences can describe the critical characters of the acoustic interference pattern in the waveguide with a satisfying precision.     

Numerical Method of Determining the Cutoff Frequency and Mode Speckle Pattern of Optical Waveguides

Based on a numerical solution of the nonstationary wave equation, an algorithm for determining the eigenfunctions and eigenvalues of the LP_im modes of axially symmetric optical waveguides is suggested. The cutoff frequency of the LP₁₁ mode of different waveguides is determined using the algorithm constructed. The results obtained are compared with the well-known analytical formulas and results of numerical calculations for the equivalent step-index waveguide model. Based on the analytical results obtained, an eigenfunction and eigenvalue search algorithm is suggested for a waveguide with a two-dimensional refractive index profile (in particular, for an axially nonsymmetric waveguide).__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 11–16, January, 2005.     

Reflection and transmission coefficients of electromagnetic waves with different polarizations on a one-dimensional layer of an inhomogeneity of the medium

We have obtained strict formulas (without approximations) for the reflection and transmission coefficients of electromagnetic waves with an arbitrary polarization in an isotropic medium with a one-dimensional layer of an inhomogeneity of an arbitrary profile playing the role of a transition layer between two different homogeneous media. Since these formulas involve values that are found by numerically integrating the first-order ordinary differential equations, the result of this paper is a fast and convenient method for calculating the above coefficients. The calculated results for two particular cases are given. An analytical limiting passage from the obtained formulas to the particular case of a sharp interface between the media (i.e., to known Fresnel formulas) is presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 9, pp. 1075–1086, September, 1996.This work was supported by the Russian Foundation for Fundamental Research.     

Benchmark calculations for Monte Carlo simulations of electrontransport

Benchmark calculations have been performed for electron transport coefficients with an aim to produce a body of data required to verify the codes used in plasma modeling. The present code for the time resolved Monte Carlo simulation (MCS) was shown to represent properly DC transport coefficients in a purely electric field, in crossed electric and magnetic fields, and in the presence of nonconservative collisions, ionization, and attachment. In addition, we have suggested tests of the time dependent solutions. Relaxation of the initial transport coefficient may serve as an accurate test of the code as well as the input data for some fluid codes. In this paper, we show only one example, but several different sets of conditions and cross sections should be used as well. Finally, we propose application of the quasi-steady state results in RF fields. As an example we suggest calculation of the components of diffusion tensor showing anomalous longitudinal diffusion and calculations made with nonconservative collisions (ionization in this case). We also check the application of approximate formulas to determine drift velocity on the basis of total collision frequency and to determine a diffusion coefficient by using the Einstein relation. Other tests required to verify the transport data calculations are discussed as well     

Effect of coherence property of incident light on prism waveguide coupling

The accurate reflection coefficient of prism waveguide coupler that takes coherence property of incident light into account is obtained at first. Based on the reflection coefficient, the effect of coherence property of incident light on prism coupling is discussed in this work. It is shown that extra damping in waveguide caused by the coherence property is larger for high-order resonant mode than that for low-order mode. For 100 fs Gaussian pulses incidence, the reflected spectra at different resonant modes are obtained theoretically and experimentally, which show that coherence property has a strong effect on prism coupling at high-order modes.     

Reflection of plane waves from an elastic layered medium: Resonance approach and numerical modeling

The resonance formalism developed earlier by H. Überall for a model of a liquid layer overlying a liquid halfspace is extended to a model of an elastic layer overlying an elastic halfspace. Using the Thomson—Haskell matrix technique, an exact analytical expression is obtained for the complex reflection coefficient. Characteristic equations are derived, and their roots, which determine the positions of the resonances of the reflection coefficient for longitudinal and transverse waves, are obtained analytically. In the resonance approach, the exact expression for the reflection coefficient is replaced by an approximate one that describes the behavior of the reflection coefficient near the resonances. The comparison of the exact and approximate values of the reflection coefficient shows good agreement between the results near the frequency and angular resonances.     

Reflection characterization of multilayer surface films

The reflection of linearly polarized light from a multilayer system of ultrathin dielectric surface films is investigated both analytically in the long-wavelength limit and numerically by the standard way of calculating the reflection characteristics for the layered medium. The second-order approximate formulas for reflection coefficients and characteristic reflection angles are derived and their accuracy is estimated. It is shown that approximate expressions obtained for reflection parameters of multilayer system in the long-wavelength limit are of immediate interest to the solution of the inverse problem for ultrathin layered surface structures. Innovative possibilities for optical diagnostics are generated by means of polarizing and principal angles. For determining the parameters of multiple surface layers an appropriate method is found by combining differential reflectance with ellipsometry.     

多天线信道空间衰落相关性近似算法及其复杂性研究

信道空间衰落相关性(SFC)主要取决于波达信号的功率方位谱(PAS)和多天线阵列收发模式.深入研究了移动通信系统中多天线阵列SFC近似计算法及其复杂性.首先导出在典型PAS为均匀分布、高斯分布以及拉普拉斯分布下的SFC函数的闭合表达式.再研究在波达信号PAS小角度扩展时的近似计算法,建立多输入多输出(MIMO)多天线接收信道模型,深入分析所选择的天线阵列和电波传播参数对MIMO系统信道容量的影响.通过理论计算和仿真实验得出近似计算法在特定条件下具有很好的拟合度,定量分析了近似计算法在对MIMO多天线系统分析时的适用性和计算效率.该算法能极大地减低理论计算复杂性,提高分析和仿真MIMO多天线系统的效率.     

Reflection coefficient of low-energy ions as a universal function of the scaled transport cross section

Multiple collision theory of heavy ion ranges in an infinite medium has been used to calculate the reflection coefficient from the penetration profile, by a method first described by Bottiger et al. Interaction with target electrons has been neglected and nuclear collisions have been described by the power cross sections. Calculations are restricted to low reduced ion energies )₀А.1 and to target/ion mass ratios 7⢪, when electronic stopping is much less than the nuclear stopping. The Gaussian approximation of the penetration profile and the reflection coefficient are found in a form of simple analytic formulas. Furthermore, the penetration profile was constructed by using Edgeworth expansion and moments of the distribution up to the fourth order, and the reflection coefficient was determined from the profile. Good agreement between the analytical results and the reflection coefficient obtained from Edgeworth expansion was found, for target atom/ion mass ratios 7̿.3. It is shown that the reflection coefficient is a universal function of the scaled transport cross section. The scaling is fulfilled for v̀, when ion reflection is determined by large-angle multiple collisions, and breaks down for v<1 i.e. 7<1, when scattering angles are small. Results are compared with TRIM computer simulation data.