When is the wave function single-valued?

It is shown that single-valuedness of the wave function can be lost because of an external field approximation. The Aharonov-Bohm effect is studied in detail as an example of the problem. Specifically, it is shown that the solenoid (represented as a rotating, charged cylinder) has a wave function that undergoes a phase shift equal in magnitude, but with opposite sign, to the phase shift suffered by the electron's wave function when the electron passes the solenoid.     

Magnetic response to applied electrostatic field in external magnetic field

We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to the simple example of a spherically symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space; the pattern of the lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics.     

Stability of the flow of weakly electro-conductive fluid in the presence of a spiral magnetic field

The stability to small disturbances of the flow in a pipe of annular cross section is considered in the presence of a spiral magnetic field. The investigated duct configuration consists of two infinite coaxial cylinders between which a weakly electroconductive viscous incompressible fluid is placed, which moves under the axial pressure gradient. The azimuthal magnetic field is created by a current flowing through the central cylinder, and the longitudinal magnetic field is created by an external solenoid. The magnetohydrodynamic approximation is used. It is found that the introduction of the azimuthal magnetic field may lead to a flow destabilization as compared to the case of only the longitudinal magnetic field.     

复合磁场引导的小型化二极管初步设计

设计了一种非浸没式小型化轴向无箔二极管,其阴极发射区位于螺线管中心孔以外,采用螺线管、永磁体和软磁体构成的复合引导磁场系统。采用CST优化设计二极管结构,使其满足800 kV电压下绝缘要求; 优化设计磁场系统结构及物理参数,使其满足引导强流相对论电子束高效率传输的要求。采用粒子模拟(PIC)软件仿真电子束产生及传输过程,验证其高传输效率。设计的阳极筒直径比原结构缩小约40%,在产生同样均匀区轴向磁场强度情况下,引导磁场重量和功耗比原结构降低约40%,仿真结果显示主引导磁场0.85 T下,8 kA电流能够实现100%传输效率。     

核磁共振成像用的球形磁体和环形磁体性能比较

本文对核磁共振成像用的球形空心线圈磁体和环形空心线圈磁体的性能进行计算机模拟比较证明环形磁体在很多方面可以与球形磁体相比拟。由于环形磁体加工容易,调节方便,因而可以取代球形磁体作成像仪器的主要部件。     

Flux quantization in a hollow superconducting cylinder with a solenoid inside a cavity

The behavior of a hollow superconducting cylinder with a long solenoid inside a cavity is considered within the framework of the Ginzburg-Landau theory. The general form is found of the thermodynamic potential of the system, which describes its behavior under the influence of the solenoid's field. It is shown that the magnetic field appears inside a cavity, when the solenoid's flux is not zero. The total flux in the system changes by jumps, due to the effect of flux quantization. The dependence of the superconducting order parameter on the solenoid's flux is found, the phase diagram of the superconducting states is analyzed. The hysteresis transitions in the system are investigated, as well as oscillations of the critical temperature and of the specific heat of the cylinder. The connection with the paper of G. Kunstatter, M. Revzen, and L. E. H. Trainor (Ann. Phys. (N.Y.)145 (1983), 329), where the corresponding problem was first touched upon, is discussed.     

基于麦克斯韦方程的交变电流长螺线管磁场

为了分析方波驱动长螺线管内磁场畸变机理,利用麦克斯韦方程研究了螺线管内外的磁场分布情况。首先,利用麦克斯韦方程,分别建立了正弦波驱动螺线管内外电场、磁场模型,并结合安培环路定律和电磁感应定律选取了合适的边界条件,得到了正弦波驱动长螺线管的磁场分布;其次,通过傅里叶变换将方波信号变换为多个正弦信号叠加的形式,从而得到了方波驱动长螺线管磁场分布;最后,通过仿真试验重点分析了方波驱动信号频率对磁场的影响,并得出结论:方波驱动长螺线管磁场波形会失真、畸变,驱动信号频率较低、距离螺线管轴线距离较近处,磁场的方波特性较好。     

Skyrmions on an elastic cylinder

For a spin-polarized electron gas on an elastic cylinder in an external axial magnetic field and an axial electric field we find that the corresponding Euler-Lagrange equation is the double sine-Gordon (DSG) equation with an exact 2π-skyrmion solution. The DSG skyrmion is stabilized, without Coulomb repulsion, by the curvature of the cylinder. It adopts a characteristic length ξ which is smaller than the radius of the cylinder. For an elastic cylinder this mismatch of length scales causes a deformation of the cylinder in the region of the skyrmion. Received 23 October 2001 / Received in final form 8 March 2002 Published online 2 October 2002 RID="a" ID="a"e-mail: rossen.dandoloff@ptm.u-cergy.fr     

The effect of a magnetic field on the crossover from the linear to quadratic frequency dependence of phononless hopping conductivity in disordered systems

The effect of an external magnetic field on the frequency dependence of phononless hopping conductivity in disordered system is studied. The dependence of the low-temperature phononless conductivity on the applied magnetic field is established. It is shown that in the limit of a strong magnetic field, the frequency of the transition (crossover) from linear to quadratic frequency dependence of phononless conductivity grows logarithmically with the value of a magnetic field.     

Magnetoplasma oscillations of a two-dimensional electron layer in a bounded system

The spectrum of magnetoplasma oscillations of a two-dimensional electron layer in a transversal magnetic field is studied under the condition that the electron system is unbounded along the layer plane and screened in the perpendicular direction. It is shown that under certain conditions oscillation frequencies much lower than the electron cyclotron frequency exist. Also the electromagnetic wave-guided oscillations in the system are described. It is shown that a strong magnetic field causes a frequency shift and splitting, depending inversely on the external magnetic field and the transversal specific dimension.     

Interaction of a Relativistic Electron Beam with a Plasma

The dispersion relation for the interaction of a relativistic electron beam in a thermal plasma, in the absence of an external magnetic field, is studied. It is shown that there are two distinct beam-plasma branches present, and that one of them couples to the electromagnetic eigenmode of the beam-plasma system with a magnetic field and a Poynting flux associated with it. It is also shown that these branches can couple together.     

Electromagnetic field perturbation by an internal void in a conducting cylinder excited by a wire loop

A thin prolate spheroidal void in an infinite conducting circular cylinder is used to model an internal flaw in a wire rope. The rope is excited by an electric ring current which is a model for a thin solenoid or multi-turn wire loop. The anomalous external fields are computed from the induced electric and magnetic dipole moments of the void. For this type of excitation, the induced axial magnetic dipole moment is the dominant contributor to the scattered field. The results have application to nondestructive testing of wire ropes.     

Filamentation of a rotating electron beam in a magnetized plasma

Filamentation of a nonrelativistic rotating electron beam in a magnetized plasma is investigated by solving the kinetic equation and finding its dielectric permitivity. The period and the establishment time of the filamentation structure and threshold for instability development are obtained. It will be shown that only when the external magnetic field strength becomes smaller than a characteristic value, filamentation appears.     

Exchange interaction and oscillations of the magnetization of the electron gas in a quantum cylinder

The exchange energy of the electron gas on a cylindrical surface in a constant magnetic field has been calculated. Analytical formulas describing the contribution of the exchange interaction into oscillations of the magnetization of the electron gas in a quantum cylinder have been obtained. It is shown that the magnetic response of the system exhibits Aharonov-Bohm oscillations for both degenerate and Boltzmann electron gases.     

Experimental investigation of magnetohydrodynamic action on a heat flux toward the surface of a model

Experimental data for magnetohydrodynamic (MHD) action on a supersonic nitrogen flow about an axisymmetric model are presented. The experiments were carried out in the Big Shock Tube (Ioffe Physical-Technical Institute), at the end of which a test section equipped with a supersonic nozzle was mounted. A test conic model coupled with a cylinder is attached to the output cross section of the nozzle. A magnetic field is produced by a solenoid placed on the cylindrical part of the model through which a pulsed current due to an external voltage source discharging passes. Electrodes on the conic part of the model initiate a gas discharge, which rotates about the axis of the model in the solenoidal magnetic field. The influence of the magnetic field on the gasdynamic pattern of the flow near the model and on the heat flux toward its surface is investigated. Schlieren patterns of the flow about the model, photographic scans of the discharge glow, and heat flux measurements are taken. It is found that the magnetic field has an effect on the gasdynamic pattern of the flow near the model and on the heat flux toward its surface. The dependence of MHD effects on the external voltage polarity is also revealed.     

Nonadiabatic screening of proton charges in the case of tunneling methyl groups in external magnetic field

The equation of motion corresponding to methyl groups embedded in solid lattices and reorienting around their symmetry axes is considered in the presence of external magnetic field. It is known that the Born-Oppenheimer approximation does not describe the electronic screening of the magnetic field as seen by the nuclei, i.e., the protons interact with the magnetic field with their bare charges. To obtain the screening, one has to include the non-adiabatic terms in the analysis. Using the rotating coordinate system fixed to the methyl group, we have shown that the effective chargeq, describing the interaction of the protons with the magnetic field, satisfiesq>0.24e (–e is the electron charge). The possibility of experimental verification is also discussed.     

Transport and focusing of a low-energy electron beam in low-pressure ionized argon

The transport and focusing of low-energy electron beams with effective transfer of stored energy in low-pressure ionized argon are investigated under the conditions of a high degree of charge neutralization in an external longitudinal magnetic field. It is shown that a nonuniform magnetic field provides the range of parameters where one can tightly stabilize the position of the maximum of the beam on the target and, if necessary, compress the beam. It is demonstrated that the parameters of the electron beam can be controlled by appropriately selecting the configuration of the magnetic field matched to self-fields.     

Toroidal plasma rotation induced by the dynamic ergodic divertor in the TEXTOR tokamak

The first results of the Dynamic Ergodic Divertor in TEXTOR, when operating in the m/n=3/1 mode configuration, are presented. The deeply penetrating external magnetic field perturbation of this configuration increases the toroidal plasma rotation. Staying below the excitation threshold for the m/n=2/1 tearing mode, this toroidal rotation is always in the direction of the plasma current, even if the toroidal projection of the rotating magnetic field perturbation is in the opposite direction. The observed toroidal rotation direction is consistent with a radial electric field, generated by an enhanced electron transport in the ergodic layers near the resonances of the perturbation. This is an effect different from theoretical predictions, which assume a direct coupling between rotating perturbation and plasma to be the dominant effect of momentum transfer.     

Dielectric response of cylindrical nanostructures in a magnetic field

We study the magnetic field dependence of the dielectric response of large cylindrical molecules such as nanotubes. When a field-induced level crossing takes place, an applied electric field has two effects: it may cause a linear instead of the usual quadratic Stark effect or the difference in the quadratic Stark coefficient of the two levels leads to a discontinuity in the polarization. Explicit calculations are performed for doped nanotubes and a rich structure in the real part of the low-frequency dielectric function is found when a magnetic field is applied along the cylinder axis. It is suggested that studies of can serve as a spectroscopic tool for the investigation of large ring-shaped or cylindrical molecules. Received 11 January 2000 and Received in final form 19 May 2000     

A Mathematical Representation of Quantizing the Motion of Relativistic Electrons in a Magnetic Field

It is shown that the quadratic component of the kinetic energy of continuous longitudinal motion of relativistic electrons in the external magnetic field is varied continuously between 0 and 2(2m _e c ²_B H) within each Landau energy level, undergoing an abrupt change at the boundaries of the levels. This results in the fact that in the quantum limit of a superstrong magnetic field where all electrons are at the zero Landau level, the maximum quadratic component of the kinetic energy of free longitudinal electron motion along the direction of the magnetic field is twice as high as the maximum quadratic component of the kinetic energy of its bound transverse motion.