Levitation Force Between a Small Magnet and Superconducting Sphere

Based on the Meissner effect and the image method, we studied the interaction between a magnetic point dipole and a superconducting sphere. We obtained analytical expressions for the interaction energy and the levitation force when the dipole is in an arbitrary orientation. Our calculations show the validity of using the image method for a antisymmetrical superconducting sphere-magnet system. Results show that the energy and the force are maxima when the magnetic dipole is perpendicular to the surface of superconductor and minima when it is tangent to the surface. Furthermore, the force acting on the tip of a magnetic force microscope above a superconducting sphere was derived as a generalization of the levitation force acts on a point dipole.      

Superconducting Sphere and Finite-Size Permanent Magnet: Force, Torque, and Alignment Effect Calculation

Using a local first-order interaction model, previously described, the force and torque between a superconducting sphere in the Meissner state and a finite-size permanent magnet are calculated. These findings are compared to results obtained by other models for the force based on the images method for a point magnetic dipole. It is demonstrated that the first-order calculation is a good approximation. Moreover, the torque between a superconducting sphere and a magnet in different positions and angular orientations is calculated for the first time. We describe the alignment effect that tends to align a magnet tangentially to the superconducting sphere surface. In addition, it is shown that the finiteness of the magnet reduces the magnitude of the repulsive force.     

Interaction Force Between a Magnetic Tip and a High Temperature Superconducting Cylinder

Based on the dipole-dipole model and the critical state model, we derived analytical expressions for the levitation force between the magnetic tip and the finite superconducting cylinder in two states: the Meissner state and the critical state. The effect of the geometrical parameters of the levitating system on the force was investigated.     

Size Effects on Levitation Force Between a Magnet and a Superconducting Thin Film in the Meissner State

The levitation force between a permanent magnetic disk and a thin superconducting disk in the Meissner state is calculated using the dipole–dipole interactions model. The levitation force as a function of the magnet and superconductor radii, the levitation height, and the superconductor thickness is studied under the assumption that the radius of the magnet is much smaller than the radius of the superconductor. Results showed an increase in the levitation force as a function of the radius of the superconducting disk. However, the levitation force decreases as the radius of the permanent magnetic disk increases. Demagnetizing effects are taken into account by considering the appropriate demagnetizing factor for the suggested system.     

Correlations Between Magnetic Flux and Levitation Force of HTS Bulk Above a Permanent Magnet Guideway

In order to clarify the correlations between magnetic flux and levitation force of the high-temperature superconducting (HTS) bulk, we measured the magnetic flux density on bottom and top surfaces of a bulk superconductor while vertically moving above a permanent magnet guideway (PMG). The levitation force of the bulk superconductor was measured simultaneously. In this study, the HTS bulk was moved down and up for three times between field-cooling position and working position above the PMG, followed by a relaxation measurement of 300 s at the minimum height position. During the whole processes, the magnetic flux density and levitation force of the bulk superconductor were recorded and collected by a multipoint magnetic field measurement platform and a self-developed maglev measurement system, respectively. The magnetic flux density on the bottom surface reflected the induced field in the superconductor bulk, while on the top, it reveals the penetrated magnetic flux. The results show that the magnetic flux density and levitation force of the bulk superconductor are in direct correlation from the viewpoint of inner supercurrent. In general, this work is instructive for understanding the connection of the magnetic flux density, the inner current density and the levitation behavior of HTS bulk employed in a maglev system. Meanwhile, this magnetic flux density measurement method has enriched present experimental evaluation methods of maglev system.     

3D Modeling Permanent Magnet Guideway for High Temperature Superconducting Maglev Vehicle Application

A three-dimensional analytical method is proposed to model the permanent magnet guideway (PMG) involved in the high-temperature superconducting (HTS) maglev vehicle system, and with this analytical method, the non-uniformity of magnetic field along the longitudinal direction of the PMG due to the existent gap between the adjacent permanent magnet (PM) can be taken into account in the simulation of the HTS maglev vehicle system. The analytical expressions for two rectangular PM with different magnetization directions are deduced from the Biot–Savart’s law. The 3D modeling of the PMG is validated from the four aspects, i.e., the comparison of the measurement and calculation value of the magnetic field; the magnetic field contour of the PMG; the comparison of the 3D method results with the 2D method; and the comparison of the results from the present 3D analytical model and previous finite element software. Currently, using the 3D analytical model, we have proposed a 3D method to numerically investigate the HTS magnetic levitation/suspension system with bulk high-temperature superconductor (HTSC).     

Magnet Guideways for Superconducting Maglevs: Comparison Between Halbach-Type and Conventional Arrangements of Permanent Magnets

The characteristics of the permanent magnets composing the guideway in superconducting magnetic levitation devices are very important for their performance in terms of levitation force and stability. From a model based on minimizing the magnetic energy in the superconductor and considering realistic parameters of actual maglev devices, we calculate the levitation and guidance forces and stability arising from both conventional arrangements and recently proposed Halbach-like arrangements. When a comparison is carefully made under similar conditions, we conclude that not always complicated arrangements based on Halbach arrays bring significant improvements with respect to some simpler arrangements that also provide large force. These results may help improving the design of actual maglev devices.     

Calculation of Levitation Force between Small Superconducting Cylinder and Magnetic Ring in the Critical State

Levitation force between a small superconducting cylinder in the mixed state and a magnetic ring was calculated using the critical state model. The dependence of the levitation force on the size of the superconductor as well as the magnet was investigated. The finite size effect of the superconductor is included by demagnetizing factor approximation. The stiffness for the levitating system was calculated. The position of the maximum levitation force depends on the size of the superconductor and the magnet. Trend of the calculated force is in agreement with the experimental results.      

Numerical Analysis on Laser-Generated Guided Elastic Waves in a Hollow Cylinder

Numerical analyses are presented for laser-generated guided elastic waves in a hollow cylinder. Time-dependent displacement at the outer surface of a hollow cylinder is expressed by summation of longitudinal and flexural type modes by employing the normal mode expansion (NME) method, then the transient waveforms excited by a single beam of laser pulse and four beams of laser pulse with an axisymmetric spatial distribution are calculated numerically. The influence of the spatial distribution of laser pulses on the waveforms are discussed in detail, and the features of major modes are explained based on dispersion curves. Finally, the total waveform of longitudinal modes obtained by the NME method is compared to that predicted by the finite element method (FEM), and a good agreement is obtained.     

Analysis of Transient Heat Conduction in a Hollow Cylinder Using Duhamel Theorem

The objective of this paper is to derive the mathematical model of two-dimensional heat conduction at the inner and outer surfaces of a hollow cylinder which are subjected to a time-dependent periodic boundary condition. The substance is assumed to be homogenous and isotropic with time-independent thermal properties. Duhamel’s theorem is used to solve the problem for the periodic boundary condition which is decomposed by Fourier series. In this paper, the effects of the temperature oscillation frequency on the boundaries, the variation of the hollow cylinder thickness, the length of the cylinder, the thermophysical properties at ambient conditions, and the cylinder involved in some dimensionless numbers are studied. The obtained temperature distribution has two main characteristics: the dimensionless amplitude ( $A$ ) and the dimensionless phase difference ( $\varphi $ ). These results are shown with respect to Biot and Fourier and some other important dimensionless numbers.     

Thermal Analysis of a Superconducting Magnet Stabilization Using a 3D Simulative Finite Element Model

Quench behavior is an important issue in stability of superconducting magnets for practical applications. A 3D FEM model was developed to study the cryogenic stabilization of a solenoid magnet. The magnet is a ‘notched’ superconducting solenoid of 170 mm in inner diameter, 223.8 mm in outer diameter and 504 mm in length which has been designed, and manufactured by a group comprising the members from Technical Institute of Physics and Chemistry (TIPC) and Institute of Modern Physics (IMP) Chinese Academy of Sciences (CAS). Quench behaviors, such as minimum quench energies and current decay, are also studied by this model. The calculated results based on this model are in good agreement with the experimental data presented by Martin N. Wilson.     

二硼化镁超导线带材及磁体应用研究进展

由于具有超导转变温度（39K）较高,晶体结构简单,原材料成本低廉以及长线制备容易等一系列特点,金属间化合物二硼化镁（ MgB2）超导体自2001年被日本科学家发现以来,引起人们广泛的关注,被认为是目前最有可能首先实现大规模工业应用的超导材料。尤其在制冷机工作温度（15～20 K）、较低磁场（1～2 T）条件下的医疗核磁共振成像仪（ MRI）超导磁体应用上有着广泛的前景。本文主要围绕实用化 MgB2超导长线（带）制备研究而展开,重点回顾了近年来粉末套管法、连续粉末装管成型法及中心镁扩散法等MgB2超导线（带）材制备及加工方面的最新研究进展;同时综述了在 MgB2超导线带材工程临界电流密度性能改进方面的最新研究工作;最后,对近几年来 MgB2超导磁体及线圈等应用研究进展进行了回顾。     

Rotor Position Estimation for Permanent Magnet Synchronous Machines using Electromotive Force and Anisotropy Using Extended-Kalman-Filter

In this paper a new rotor position observer for permanent magnet synchronous machines (PMSM) based on an Extended-Kalman-Filter (EKF) is presented. With this method, just one single EKF is sufficent to evaluate the position information from electromotive force (EMF) and anisotropy. Thus, the PMSM can be controlled for the entire speed range without a position sensor and without the need to switch or synchronize between different observers. The approach covers online estimation of permanent magnetic field and mechanical load. The resulting EKF-based rotor position estimator is embedded in the existing cascaded control concept of the PMSM without need of additional angle trackers or signal filters. The experimental validation for the position sensorless control shows optimized dynamic behaviour.

     

Analysis of Photonic Band Gaps in a Two-Dimensional Triangular Lattice with Superconducting Hollow Rods

In this work, we use the plane wave expansion method to calculate photonic band structures in two-dimensional photonic crystals which consist of high-temperature superconducting hollow rods arranged in a triangular lattice. The variation of the photonic band structure with respect to both, the inner radius and the system temperature, is studied, taking into account temperatures below the critical temperature of the superconductor in the low frequencies regime and assuming E polarization of the incident light. Permittivity contrast and nontrivial geometry of the hollow rods lead to the appearance of new band gaps as compared with the case of solid cylinders. Such band gaps can be modulated by means of the inner radius and system temperature.     

Thermo-Stressed State of a Hollow Polymer Dielectric Cylinder

Journal of Engineering Physics and Thermophysics - The paper presents a mathematical model describing the distribution of stresses in a hollow cylinder caused by a one-dimensional steady...     

Wide Variety of Experiments Using a Cryogen-Free 27.5 T Hybrid Magnet and a Cryogen-Free 18.1 T Superconducting Magnet

A cryogen-free hybrid magnet without liquid helium for operation, generating 27.5 T in a 32 mm room temperature bore of an 8 MW water-cooled resistive insert magnet in an 8.5 T background field of a cryogen-free superconducting outsert magnet, is being operated for basic research at low temperatures down to 17 mK in combination with a dilution refrigerator. In addition, we are developing functional materials using a differential thermal analysis DTA at high temperatures up to 1473 K in high fields up to 27 T. This cryogen-free hybrid magnet will be upgraded to generate 29 T by improving the outer superconducting magnet. A cryogen-free 18.1 T superconducting magnet with a 52 mm room temperature experimental bore, consisting of a Bi₂Sr₂Ca₂Cu₃O₁₀ (Bi2223) insert coil, has been developed using a GM-JT cryocooler. Recently, bronze-tape-laminated Bi2223 has revealed excellent irreversible stress tolerance of 250 MPa at 77 K. In addition, the critical current properties for recent Bi2223 tapes are largely improved from 200 to 400 A/cm-width at 77 K in a self-field. Therefore, the stainless steel reinforcement tape incorporated for the previous Bi2223 insert coil is no longer needed for a new Bi2223 one. A new Bi2223 insert coil with almost the same size as the existing insert coil can generate two times higher fields at the elevated operation current from 162 to 191 A. An upgraded cryogen-free superconducting magnet can offer a long-term experiment at the constant magnetic field of 20 T for an in-field heat-treatment investigation.     

中小型超导磁体用低温恒温器的安全

从工作压力角度分析了中小型超导体磁作用低温恒温器的安全问题，并给出了超导磁体猝灭引起低温恒温器压力变化的实验观察实例，以及超导Ｗｉｇｇｌｅｒ磁体低温恒温器的安全设计。     

永磁同步驱动电机运行性能与振动分析

驱动电机的运行性能和振动分别影响电动汽车的动力性和乘坐舒适性.考虑较多学者仅对电机运行性能或振动性能进行单独研究存在不足的情况,采用数值计算方法分析8极48槽同步电机的运行性能和振动响应.先建立二维有限元模型并验证模型正确性;然后进行运行性能和分析,发现其输出功率效较高,但其转脉动值较大,约为27.12％;最后进行振动...     

Development of a Superconducting Magnet System with Zero Liquid Helium Boil-off

A homogeneous magnetic field superconducting magnet with a cold bore of 250 mm and a central field of 4.3 T has been designed, manufactured, and tested with zero liquid helium boil-off. As a result of magnetic field homogeneity considerations, the magnet is composed of three coaxial coils: one main coil and two compensation coils. All coils are connected in series and can be charged with a single power supply. The magnetic field homogeneity is about ±3.0 % from ?200 mm to 200 mm in axial direction with 86 mm in diameter. The magnet can be operated in persistent mode with a superconducting switch. A two-stage GM cryocooler with a capacity of 1.5 W at 4.2 K was used to cool the superconducting magnet. The cryocooler prevents the liquid helium from boiling off and leads to zero helium loss during static operation. The magnet can be operated in liquid helium circumstance by cooling the gas helium with the cryocooler without additional supply of liquid helium. Under this condition, the magnet is successfully operated up to 4 T without quench. The magnet system can be generating 0.25 L/h liquid helium with the cryocooler by supplying the gas helium without loading the magnet. In this paper, the magnet design, manufacture, mechanical behavior analysis, and the performance test results of the magnet are presented.