无引导磁场Raman自由电子激光实验的理论分析

本文分析Raman自由电子激光中常用的双绕螺旋线摇摆器的自聚焦过程和自聚焦能力,得出束流稳定传输的条件,并与无引导磁场Raman自由电子激光实验中测得的传输束流进行分析比较。文中还对在电子脉冲线加速器EPA-74上完成的无引导磁场自由电子激光实验的辐射输出进行分析。理论分析与实验结果相符合。 关键词：     

圆柱螺旋电磁Wiggler的场形分析

 利用载流圆柱螺旋线系统内部的磁标势满足的Laplace方程, 以及系统磁矢势的积分形式, 定出Laplace方程通解的未知系数, 求得左(右)旋单绕圆柱螺旋线的磁标势。应用磁场的叠加原理以及积分法, 给出了各种类型如双绕、双双绕、交叉绕等螺旋形Wiggler的场形分布公式。     

分流环型绝热过渡区双绕螺旋线Wiggler束流传输实验

束流传输实验结果表明，分流环型过渡区双绕螺旋线圆极化Ｗｉｇｇｌｅｒ的端口区磁场，具有良好对称性，能基本保证磁场强度由零绝热过渡到均匀区，没有磁场畸变，因而对电子束流的能散度影响小，端口束流损失少。当入口端γ＝２的５００Ａ束流时，有约３５０Ａ束流传输到均匀区，而在相同条件下，喇叭口型绝热过渡区Ｗｉｇｇｌｅｒ只有１２０Ａ的束流传输到３４ｃｍ处的均匀区。分流环型变磁场技术可用于双绕螺旋线Ｗｉｇｇｌｅｒ变参自由电子激光。     

通电圆线圈轴线上磁场分布分析

由毕奥一萨伐尔定律导出通电圆线圈轴线上磁场分布公式．由该公式出发推出一个更适用的表达式,并据此分析了单线圈的磁场和双线圈合成磁场．用标准偏差理论分析了两线圈间距取不同值时,两线圈间磁场的均匀程度．     

磁化等离子体填充螺旋线的色散方程

利用等离子体流体理论和纵向场分量法，结合螺旋线的导电面模型，对在有限磁场作用下，填充等离子体的螺旋线进行了严格的场分析. 在给出各区域电磁场分量表达式的基础上，利用螺旋线的边界条件，导出了磁化等离子体填充螺旋线中电磁波传播所满足的色散方程，并对所导出的色散方程进行了讨论. 关键词： 有限磁场 等离子体 螺旋线 色散方程     

新型反绕双螺旋线慢波系统的分析与设计

 基于降低工艺难度的目的,提出了一种新型反绕双螺旋线慢波系统,该系统的正绕反绕螺旋线半径不等。利用3维电磁软件CST MWS仿真分析了结构参数对色散和耦合阻抗的影响。结果表明：耦合阻抗在螺旋带内半径较大时没有明显下降;减小螺旋带宽度有利于降低相速度和提高耦合阻抗;在一定范围内,相速度随螺距的减小而增大。在此基础上,结合工程要求设计了8 mm波段行波管的新型反绕双螺旋线慢波系统,耦合阻抗达到21 Ω,工作电压约为20 kV,同时由于电子通道半径较大,降低了对电子光学系统的要求;纵向翼片加载的引进较为有效地展宽了带宽。     

金属中逆法拉第效应的经典理论

研究电子在圆偏振光驱动下的经典动力学问题以及金属中逆法拉第效应(IFE)的经典微观机制.得到电子在圆偏振光驱动下的一个解,表明其运动轨道是螺旋线.忽略电子与磁场的相互作用,电子作绕平行于其初速度的轴、横截面为椭圆的螺旋线运动,产生了一个平行于其初速度、方向由圆偏振光的手征性决定的磁矩.磁矩的统计结果与Hertel从电子气整体出发得到的结果一致.     

左右旋双双绕螺旋线线极化摇摆器的磁场分布及束流传输

给出了双双绕螺旋线线极化Wiggler轴线上磁场的积分表达式,以此公式数字模拟此装置端口区的磁场分布,并进行了实验测定,结果表明,端口区磁场峰值突变和对称性均比圆极化好。另一方面,用洛仑兹运动方程,考虑了电子束空间电荷效应,证明此装置对电子束传输有自聚焦能力,给出了电子运动方程,电子束流与Wiggler峰值磁场的关系,数字模拟电子束运动轨迹也表明,此装置能自聚焦传输电子束,有希望应用于线极化自由电子激光实验中。     

水介质Blumlein型螺旋脉冲形成线的研究

 分析了螺旋线脉冲形成线脉宽加宽的原理,利用程序对Blumlein型螺旋脉冲形成线进行了模拟研究,模拟结果与理论分析得到的脉宽表达式吻合较好,并可以给出螺旋线中筒的电场和磁场分布。加工了一套Blumlein型螺旋脉冲形成线,并开展实验研究,解决了绝缘支撑耐压问题,得到充电电压550 kV,二极管电压500 kV,电流28 kA,半高宽128 ns的脉冲输出。     

平行共轴线圈的磁场特征研究与实验设计

通过计算机及相关的传感器和数据采集接口辅助,研究了平行共轴双线圈间距分别为0.5R,R,1.5R时,轴线方向磁场强度的分布规律及特征.从平行共轴双线圈间距为R的亥姆霍兹线圈所形成的均匀磁场出发,结合理论推导,自己设计并组装了三线圈实验装置,实现了平行共轴三线圈均匀磁场区域扩大、强度增强的实验设计,在一定程度上弥补了传统亥姆霍兹线圈磁场测量的不足并有助于对其深入的理解和研究.     

Simulation of induction at low magnetic Prandtl number

We consider the induction of a magnetic field in flows of an electrically conducting fluid at low magnetic Prandtl number and large kinetic Reynolds number. Using the separation between the magnetic and kinetic diffusive length scales, we propose a new numerical approach. The coupled magnetic and fluid equations are solved using a mixed scheme, where the magnetic field fluctuations are fully resolved and the velocity fluctuations at small scale are modeled using a large eddy simulation (LES) scheme. We study the response of a forced Taylor-Green flow to an externally applied field: topology of the mean induction and time fluctuations at fixed locations. The results are in remarkable agreement with existing experimental data; a global 1/f behavior at long times is also evidenced.     

Model of line preserving field line motions using Euler potentials

We consider behavior of finite magnetic field lines during reconnection processes. We portray field line motions using Euler potentials representation. Here, we propose a new insight into plasma flow fields related with magnetic reconnection. In this approach reconnection is treated as a breakage of magnetic topology, which results in deviation from the line preserving flow regime. We derive constraints and the general equations for these flows. In our approach the flux preserving flows are treated as a special case of line preserving regime. We also derive a constraint on a non-ideal term in Ohm’s Law within diffusion regions, which relates plasma flow with resistivity, and which must hold for non-reconnective diffusion. We also propose a new method of detecting magnetic reconnection.     

Phonon-assisted tunneling and shot noise in double barrier structures in a longitudinal magnetic field

The phonon-assisted resonant tunneling is studied for the double barrier structures in a longitudinal magnetic field. Using the scattering matrix approach with an appropriate one-particle Green's function we are able to calculate the current and the zero frequency shot noise power spectrum in a large range of the magnetic field and to any order of the electron-phonon interaction. Obtained results describe well the relevant experimental data and provide new suggestions for further examinations.     

Negative Magnetoresistivity of ErBi and Its Crystal-Field Levels

A theoretical approach is generalized and employed in this work to evaluate the magnetoresistivity of ErBi in external magnetic fields. The calculated results and theoretical analyses show that when an external magnetic field is applied in the z-direction, the magnetoresistivity can be reduced considerably due to the degeneracy lifting of the crystal-field levels. However, when the magnetic field is exerted along the x-axis, the magnetoresistivity will be increased because of the formations of new magnetic states of the Er ion and its transitions within and between these new states.     

Spin-flavor oscillations of Dirac neutrinos described by relativistic quantum mechanics

Spin-flavor oscillations of Dirac neutrinos in matter and a magnetic field are studied using the method of relativistic quantum mechanics. Using the exact solution of the wave equation for a massive neutrino, taking into account external fields, the effective Hamiltonian governing neutrino spin-flavor oscillations is derived. Then the The consistency of our approach with the commonly used quantum mechanical method is demonstrated. The obtained correction to the usual effective Hamiltonian results in the appearance of the new resonance in neutrino oscillations. Applications to spin-flavor neutrino oscillations in an expanding envelope of a supernova are discussed. In particular, transitions between right-polarized electron neutrinos and additional sterile neutrinos are studied for realistic background matter and magnetic field distributions. The influence of other factors such as the longitudinal magnetic field, the matter polarization, and the non-standard contributions to the neutrino effective potential, is also analyzed.     

Control of the binding energy by tuning the single dopant position,magnetic field strength and shell thickness in ZnS/CdSe core/shell quantum dot

Recently, the new tunable optoelectronic devices associated to the inclusion of the single dopant are in continuous emergence. Combined to other effects such as magnetic field, geometrical confinement and dielectric discontinuity, it can constitute an approach to adjusting new transitions. In this paper, we present a theoretical investigation of magnetic field, donor position and quantum confinement effects on the ground state binding energy of single dopant confined in ZnS/CdSe core/shell quantum dot. Within the framework of the effective mass approximation, the Schrödinger equation was numerically been solved by using the Ritz variational method under the finite potential barrier. The results show that the binding energy is very affected by the core/shell sizes and by the external magnetic field. It has been shown that the single dopant energy transitions can be controlled by tuning the dopant position and/or the field strength.     

Magnetic field induced orbital polarization in cubic YbInNi4: determining the quartet ground state using x-ray linear dichroism

We have been able to induce a linear dichroic signal in the Yb M(5) x-ray absorption white line of cubic YbInNi(4) by the application of a magnetic field. The nonzero integrated intensity of the magnetic field induced dichroic spectrum indicates a net noncubic 4f orbital polarization. A quantitative analysis of the temperature and field strength dependence establishes that the crystal-field ground state is a Γ(8) quartet. The results demonstrate the potential of magnetic field induced linear dichroism as a new powerful approach for the investigation of the degeneracy and orbital degrees of freedom of cubic heavy-fermion and Kondo systems.     

由正负磁单极对相互作用诱导的孤立狄拉克弦

基于三维旋量Gross-Pitaevskii(GP)方程研究在含时周期性外磁场作用下玻色-爱因斯坦凝聚体的动力学行为.结果显示,在含时周期外磁场的作用下,铁磁态自旋为1的玻色-爱因斯坦凝聚体将发生拓扑形变.当磁场的两个零点进入凝聚体后,自旋向上态的密度布居图在z轴上分别形成向上和向下的凸起.随着磁场的两个零点在凝聚体内逐渐重合,向上和向下的凸起被拉长,最终自旋向上态在z轴上呈线状分布,这与理论分析预测得到的孤立狄拉克弦相对应.最后,通过计算凝聚体的超流涡度给出磁单极的表征图.结果显示,凝聚体在磁场的两个零点处形成正、负磁单极对,分别对应着自旋向上态在z轴上向上和向下的凸起.随着磁场的两个零点重合,正、负磁单极对中的两条狄拉克弦逐渐靠近,之后大约经5 ms,它们完全相连,最终形成孤立的狄拉克弦.     

Supercurrents through barriers

Superconducting systems partitioned by barriers which are thin enough to allow supercurrents to pass through them are discussed. The implications for such systems of superconducting long-range order are considered, and a phenomenological theory developed and applied to a number of topics: penetration of a magnetic field into a barrier, interference of supercurrents in the presence of a magnetic field, the cut-off frequency associated with the propagation of electromagnetic waves along a barrier, a.c. supercurrents, and structure in the d.c. current-voltage characteristics of a barrier resulting from an applied microwave field or the a.c. supercurrent. The phenomenological theory is justified by the use of microscopic theory, and a new approach, based on the Gor'kov method, is described. The results of this approach, which is of more general validity than the tunnelling Hamiltonian method, are shown to be expressible in terms of Feynman diagrams. Attention is drawn to the analogy between supercurrents and other processes involving phase coherence.     

一种新的测量大尺度冷原子团温度的方法

报道了一种新的测量大尺度冷原子团温度的方法。这种方法利用反亥姆霍兹线圈产生四极磁场,探测光沿着竖直方向逐点测量冷原子团的分布情况,获得冷原子团在不同自由下落时间下的密度分布曲线,进而拟合出冷原子团的温度值。通过实验,利用这种方法测量了积分球中冷原子团的温度,为73±12μK,并与飞行时间(TOF)方法的测量结果进行了比较。