Dimensional Magnetic Field Research Articles

Some Propagation Properties of the Iwatsuka Model

In this paper we study a two dimensional magnetic field Schrodinger Hamiltonian introduced in [7]. This model has some interesting propagation properties, as conjectured in [2] and at the same time is a special case of the class of analytically decomposable Hamiltonians [5]. Our aim is to start from a conjugate operator, intimately related to the band structure of the Hamiltonian and to prove existence of an asymptotic velocity in one spatial direction and a theorem giving minimal and maximal velocity bounds for the propagation associated to the Hamiltonian. A simple example of this model, with a very simple conjugate operator, has been given in [9]. At the same time, by using the Virial Theorem, we obtain a generalisation of the hypothesis in [7].

Semi-classical bounds on scattering cross sections in two dimensional magnetic fields

AbstractWe prove the uniform boundedness of averaged total cross sections or of quantities related to scattering into cones in the semi-classical limit for scattering by two dimensional magnetic fields. We do not necessarily assume that the energy under consideration is in a non-trapping energy range in the sense of classical dynamics.

Laser Ablation. Fabrication of Micro-Magnetic Device by Excimer Laser Ablation.

A micro-magnetic divice consisting of patterned Sr-ferrite by excimer laser ablation is described. By using a projection-patterned etching, the etched pattern of 80μm in depth is achieved in focused laser irradiation (600mJ/cm2, 10Hz, 45 minutes) in air. The magnetic properties for aspect ratio and profile of laser etched grooves are calculated by a three dimensional magnetic field analysis. Furthermore, the magnetic flux density onto the Sr-ferrite substrate is also measured by magneto-optical sensor.

Equilibrium magnetic fields and currents in a nonaxisymmetric torus: external magnetic fields in stellarators

The three dimensional (3-D) and axisymmetric (2-D) magnetic fields produced by currents flowing in plasmas that are confined in stellarators with a nearly planar geometrical axis are investigated. Using the Green's function method to solve the 3-D linear equation derived previously, a simple procedure is presented here to determine the structure of plasma induced external magnetic fields in stellarators. A detailed numerical analysis of the values of the external 3-D magnetic fields and their dependences on the plasma profiles is performed. Analytical formulas are derived that could be useful for estimations. The possibility of using the measurements of these fields for the experimental identification of the magnetohydrodynamic (MHD) equilibria is considered. Also discussed are some interesting aspects of the influence of the magnetic hump on the value of the Pursch-Schluter currents (that appear in recent Heliotron-E experiments) and the influence of different features of the vacuum magnetic field on the dipole component of plasma induced field is classified. The results of calculations related to the modern experiments are presented, and the case that may be typical for future experiments is also considered

A three dimensional finite element modelling of rotating machines involving movement and external circuit

The paper describes a combination of methods for the three dimensional magnetic field simulation of rotating machines using the finite element method. The modelling takes into account both the external circuit and movement of the rotor. The electric coils are represented in a mesh-independent fashion by the line current model. The equations from a nodal analysis of the electric circuit are solved simultaneously with the finite element equation system at each time step. The movement is treated using a finite element connection between the two independent stator and rotor meshes.

Simplified magnetic field modeling and calculation of large air-core reactor coils

A simplified magnetic field model for large air-core reactor coils is proposed. It uses three flexible magnetic dipoles with their numbers of turns and positions flexible. The magnetic flux density was calculated along 5 typical traverses for three different types of coils. At designated field points, close to the coil, the calculation error of the proposed model is less than 5%. The three flexible dipole model proposed is not only simple and easy to be implemented but also gives satisfactory accuracy in the regions of practical interest. It can be applied easily to the calculation of the three dimensional power frequency magnetic field distribution of substations.

3D line current model of coils and external circuits

The paper describes a method of three dimensional magnetic field simulation with finite elements including the eddy current problem of coils that are coupled with an electric network. The coupled problem is treated in a time stepping scheme. The electric coils are represented in a mesh-independent fashion by the line current model. The equations from a nodal analysis of the electric circuit are solved simultaneously with the finite element equation system at each time step. >

Three Dimensional Magnetic Field Analysis of A System Containing Coil Currents and Iron Elements by Virtual Current Method.

This paper proposes a method of analyzing three dimensional magnetic field of a system containing coil currents and magnetic substances using virtual currents. Various methods have been presented for analysis of three-dimensional static field of open boundary space, but, in a large-scale problem, the size of computation easily exceeds the acceptable limit of computing time and the capacity of a machine. The basic idea of the proposed method is to divide the whole region into interior and exterior region with an artificial boundary and to substitute virtual currents for source currents and magnetic substances within the boundary. The use of virtual currents reduces the number of elements for the analysis and shortens computing time while maintaining accuracy of analysis. In this paper, a method of determining virtual current is proposed and principal parameters of virtual currents which affect accuracy of analysis are examined. The conditions under which the virtual current method can be applied are examined through analysis of errors introduced by virtual current method. This method has been applied to analyze magnetic shielding of a magnet for magnetic resonance imaging. This example proves that the proposed method is effective in reducing scale of analysis and computing time.

Electron band structure in a two-dimensional periodic magnetic field.

In this paper we study the energy spectrum of a two dimensional electron gas (2DEG) in a two dimensional periodic magnetic field. Both a square magnetic lattice and a triangular one are considered. We consider the general case where the magnetic field in a cell can be of any shape. A general feature of the band structure is bandwidth oscillation as a function of the Landau index. A triangular magnetic lattice on a 2DEG can be realized by the vortex lattice of a superconductor film coated on top of a heterojunction. Our calculation indicates a way of relating the energy spectrum of the 2DEG to the vortex structure. We have also derived conditions under which the effects of a weak magnetic modulation, periodic or not, may be reproduced by an electric potential modulation, and vice versa.

Effects of Hall currents on the instability of a gravitating partially ionized plasma in a two dimensional horizontal magnetic field

The instability in a stratified layer of a self-gravitating infinitely conducting incompressible inviscid partially ionized plasma has been studied in the presence of effects of Hall currents, for a plasma permeated by a uniform two dimensional horizontal magnetic field, the proper solution has been obtained through the use of a variational principle which is shown to characterize the problem for a plasma in which the density is stratified exponentially along the vertical, the dispersion relation has been derived. Numerical calculations of the growth rate of the unstable modes of propagation have been performed from the dispersion relation for different values of the physical effects. It is found that the Hall currents have a destabilizing effect while the neutral gas frictional effects have a stabilizing influence on the instability of a conducting plasma.

Equilibrium magnetic fields and currents in a non-axisymmetric torus

This paper describes an investigation of the three dimensional (3-D) magnetic fields produced by currents flowing in plasmas that are confined in stellarators and in tokamaks with magnetic field ripples. A simple semianalytical procedure is proposed and a linear 3-D equation is derived that makes it possible to investigate the influence of finite pressure effects and plasma currents on the ripples of the longitudinal magnetic field. Analytical estimations are presented that can be useful for the analysis of the transport properties of finite beta plasmas. It is shown that the accuracy of the experimental identification of the magnetohydrodynamic (MHD) equilibria can be improved using external measurements of the 3-D magnetic fields. This method appears to have considerable promise for the investigation of fairly weak effects, as for example, for distinguishing bootstrap current profiles in stellarators. Analytical expressions for the 3-D external magnetic fields produced by plasma currents are derived that can be used for a rough interpretation of the experimental data

Three dimensional magnetic field computation by a coupled vector-scalar potential method in brushless DC motors with skewed permanent magnet mounts-the formulation and FE grids

A three dimensional finite element (3D-FE) method for the computation of global distributions of 3D magnetic fields in electric machines containing permanent magnets is presented. The formulation of this 3D-FE method including 3D permanent magnet modeling, which is based on a coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) approach, is given. The development of the necessary 3D-FE grids and algorithms for the application of the method to an example brushless DC motor, whose field is three dimensional due to the skewed permanent magnet mounts on its rotor, is also given here. A complete set of results of application of the method to the computation of the global 3D field distributions and associated motor parameters under no-load and load conditions are detailed in a companion paper. >

Three dimensional magnetic field computation by a coupled vector-scalar potential method in brushless DC motors with skewed permanent magnet mounts-the no-load and load results

The coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) method of computation of 3D magnetic fields by finite elements (3D-FE) is applied here to a brushless DC motor with skewed permanent magnet mounts on its rotor. Results of the CMVP-MSP and 3D-FE computation of the magnetic field and associated motor parameters (EMFs and armature inductances) are detailed in this paper. These results demonstrate vividly the three dimensional nature of the computed flux distributions, caused by the torque ripple reduction design employing skewed magnet mounts on the rotor. Experimental evidence supporting the validity of the BD-FE field computations, through comparison between computed and measured armature EMF waveforms is also provided in this paper.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

コールド・クルーシブルのスリット設計が磁場分布,発熱速度に及ぼす効果

In order to clarify the effects of the design parameters of a cold crucible such as the width and the number of slits on the process variables, experiments and theoretical analyses were conducted. Magnetic field was measured and an aluminium charge was melted in cold crucibles with different slit widths. The two variables of electrical resistance and inductance were introduced into an equivalent circuit model of a cold crucible and their variations caused by the change of the slit width were calculated by use of the data obtained by measuring the input power and the coil voltage. Furthermore, the three dimensional magnetic field around a cold crucible system was calculated by using of the boundary element method. To confirm the accuracy of the circuit model and the numerical analysis, the variations of the electrical resistance computed by both theoretical ways were compared with each other. By use of the three dimensional computer code, the effects of width and number of slits on the heat generation rates in the crucible, the coil and the charge were evaluated.

Three dimensional magnetic fields in extra high speed modified Lundell alternators computed by a combined vector-scalar magnetic potential finite element method

A three-dimensional (3-D) finite-element (FE) approach was developed and implemented for computation of global magnetic fields in a 14.3 kVA modified Lundell alternator. The essence of the method is the combined use of magnetic vector and scalar potential formulations in 3-D FEs. This approach makes it practical, using state-of-the-art supercomputer resources, to globally analyze magnetic fields and operating performances of rotating machines which have 3-D magnetic flux patterns. The 3-D FE computed fields and machine inductances as well as various machine performance simulations of the 14.3-kVA machine are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

ANALYSIS OF MAGNETIC FIELDS IN TRANSFORMER CORES USING PERSONAL COMPUTERS

The finite element technique has been used to develop a software package which, with the help of an IBM/PC 386 computer, can determine two dimensional magnetic fields and power loss in transformer cores. The program takes into account both the non‐linear B‐H characteristic and the anisotropy of the core material.

サンドイッチ型磁性アタッチメントに関する基礎的検討

A dental magnetic attachment has recently attracted vivid attentions from many prosthodontists for their clinical availabilities as a retainer for prostheses. Several types of dental magnetic attachments are commercially available at the moment. However none of them are clinically satisfactory. They must possess strong retention and complete corrosion resistance, since the available space is limited and the exposed magnet is easily corroded in the oral cavity.A very small and powerful attachment has been developed by devising a sandwich typed construction and the elliptic cross-section with the aid of three dimensional FEM magnetic field analysis. The attachment is sealed up with a stainless steel cap laser-welded to the yoke. It has shown sufficient attractive force (560 gf) and stability in various fundamental tests.

Three Dimensional Magnetic Field Analysis of Permanent Magnet by Boundary Element Method

Three dimensional analysis is necessary for complicated structural problems, but it requires substantial computer capacity. In this paper, the magnetic field of a permanent magnet was analyzed by the boundary element method. The calculated results were compared with measured results and were found to agree. This method reduces the computing capacity.

Effect of gauge fixing term in three dimensional stationary magnetic fields problem

Gauge fixing in 3-D stationary linear magnetic fields in a finite volume is achieved under some particular assumptions. Divergence of inner region A satisfies the Laplace equation by using a conventional gauge-fixing term to the gauge-invariant Lagrangian. Taking into account the assumed zero boundary condition for divA on the natural boundary condition surface, it is found that divA vanishes all over the region theoretically. Uniqueness of the solution is proved in another particular case. A numerical analysis is presented and the optimal value of the gauge-fixing parameter alpha is examined. >

有限要素法による二次元交流磁界解析のためのアダプティブ分割法

Fine mesh divisions are essential to obtain accurate solutions of two dimensional AC magnetic field analysis. But it requires the technical know-how to find fine mesh divisions and moreover it is complicated to divide the analysis domain. So we have developed the adaptive mesh generator using equalization of energy variation of every element and applying the technical know-how to divide the conductor or magnetic material under consideration of the skin effect by the eddy current. And we have applied this adaptive mesh generator to the loss analysis of the infinite copper-plane, and we have obtained accurate solutions.