Superconducting Levitation Research Articles

Controlled levitation of bulk superconductors

Levitation of bulk Y-Ba-Cu-O superconductors could successfully be controlled using a Bi-Sr-Ca-Cu-O superconducting electromagnet. It was found that stable levitation without tilting was obtained only when the sample trapped a certain amount of field, the minimum of which depended on the external field and the sample dimensions. We also employed a novel analysis method for levitation based on the total energy balance, which is much simpler than the force method and could be applied to the understanding of general levitation behavior. Numerical analyzes thus developed suggested that stable levitation of superconductors with large dimensions can only be achieved when the induced currents can flow with three dimensional freedom.

Magnetic damping of the electrodynamic suspension-type superconducting levitation system

The damping characteristic of the bogie motion is one of the most important issues to be investigated in the superconducting magnetically levitated system based on electrodynamic suspension (EDS). We have therefore studied the damping characteristics and the mechanism of magnetic damping. Electric circuits consisting of coil resistances and inductances can describe the electromagnetic behavior of the levitation system. By numerical calculation based on the electric-circuit equations combined with the equations of motion, damping characteristics of the bogie are examined for the system consisting only of levitation coils and superconducting coils, and also for the configuration with magnetic shielding structures incorporated. Furthermore, paying attention to the energy balance in the levitation and propulsion system when the bogie is forced to oscillate sinusoidally, we have investigated the relation between the input energy and the running speed, and compared the waveforms of levitation force and bogie oscillation to consider the characteristics and the mechanism of the damping. © 1999 Scripta Technica, Electr Eng Jpn, 127(2): 49–60, 1999

Pulse motor with high-temperature superconducting levitation

A simple but stable noncontact high T/sub c/ superconducting levitation system with a vertical shaft has been presented. The system consists of a superconductor and permanent magnets. In the system, only a high T/sub c/ superconductor supports the lower end of the shaft, and the other end is supported by two ordinary permanent magnets. Since the restoring force is small with respect to the radial direction, the system becomes unstable when the force acts in the radial direction, so it is difficult to drive the shaft by electromagnetic forces when using motors. A driving system using electromagnets has been presented, in which the balanced forces act on two opposite sides of the disc-type rotor in the axial direction. Since the system has no unbalanced force from an analytical point of view, the rotor will be able to rotate without control. In the system, however, since there is eccentricity between the center of rotation and the magnetic center, vibrations are generated. This study also presents an optimal control method for the vibrations. To validate the proposed system and the control method experimental tests have been carried out.

バルク超電導材料の基礎と応用 Ｙ‐Ｂａ‐Ｃｕ‐Ｏバルク超電導体の浮上とエネルギー解析

The levitation of bulk Y-Ba-Cu-O superconductors can be controlled using a Bi-Sr-Ca-Cu-O (Bi2223) superconducting electromagnet. It was found that stable levitation without tilting could be obtained only when the sample trapped a certain amount of fields, the minimum of which depended on the external field and sample dimensions. We employed a novel analysis method for levitation based on the total energy balance, which is much simpler than the force method and could be applied to understanding general levitation behavior. Numerical analyses thus developed showed that stable levitation of superconductors with large dimensions can only be achieved when the induced currents can flow with three-dimensional freedom.

Magnetic levitation of superconductors in the critical state

The vertical levitation force in a cylindrically symmetric system composed of a permanent magnet and a type-II superconductor is studied assuming the latter to be in a critical state. In a first step, a constant-field-gradient approximation along the length of the superconductor is used to see the effects of the dependence of the critical current density on the internal magnetic field. In a second step, the theory is generalized in order to study the case when the field gradient is not constant, as is usually found in levitation experiments with bulk superconducting samples. The model results are discussed in relation to recent experimental data on magnetic levitation of high-${T}_{c}$ superconductors, explaining the observed behavior and making some predictions for future experiments.

High temperature superconductor levitation motor

We show how it is possible to construct a high temperature superconductor levitation motor in an introductory physics laboratory. It is suitable for classroom demonstration and uses a simple yet efficient cooling method.

Mechanical stability of a high-T/sub c/ superconducting levitation system

This research deals with dynamics of a permanent magnet freely levitated above an excited high-T/sub c/ superconductor. Vertical restoring forces acting on the magnet were evaluated by analysis based on the critical state and flux flow models. The results show nonlinearity and frequency-dependence of the forces, which were observed in experiments. Vertical vibration properties of the system were also evaluated analytically by considering the above properties of the restoring forces. The results show good agreement with experimental ones, which include effect of the frequency-dependent stiffness on the resonant frequency, the primary resonance characteristics, stability of the steady-state motions and so on.

Magnetic Damping of the Electrodynamic Suspension Type Superconducting Levitation System

The damping characteristic of the bogie motion is one of the most important issues to be investigated in the superconducting magnetically levitated system based on the Electrodynamic Suspension (EDS). We have therefore studied the damping characteristics and the mechanism of magnetic damping. Electric circuits consisting of coil resistances and inductances can describe the electromagnetic behavior of the levitation system. By numerical calculation based on the electric circuit equations combined with the equations of motion, damping characteristics of the bogie are examined for the system consisting only of levitation coils and superconducting coils and also for the configuration with magnetic shielding structures incorporated. Furthermore, paying attention to the energy balance in the levitation and propulsion system when the bogie is forced to oscillate sinusoidally, we have investigated the relation between the input energy and the running speed and compared the waveforms of levitation force and bogie oscillation to consider the characteristics and the mechanism of the damping.

Modeling of lateral force-displacement hysteresis caused by local flux pinning

The permanent magnet and high- T c superconductor levitation system has a large variety of setups for positioning and scaling. The flux pinning effect of HTSC has the important role to support a permanent magnet as a flux source. As for the HTSC magnetic bearing which includes both linear and rotary systems, it positively applies the effect to guide the levitated body along the zero-gradient direction of the external field. On the other hand, the relation between force and displacement is well known to have hysteretic characteristics for the change of relative position of the permanent magnet and the superconductor. In this paper, the relation of the lateral force and the lateral displacement around the locally pinned flux on the surface of HTSC is investigated experimentally. Moreover a hysteresis model is proposed based on the experimental force and displacement relation.

Comparison of the levitation forces of melt-processed YBaCuO superconductors for different magnets

It is difficult to compare the levitation force of superconductors for different magnets. A new parameter, α, is proposed in this paper, which is defined as the ratio of a superconducting levitation force to the limitation force for a given magnet. Using this parameter, the comparison between different superconducting levitation forces in melt-processed YBaCuO superconductors (QMG) has been done, such as a levitation force of 269 kN/m 2 (=2.74 kgf/cm 2) for a superconductor 77.3 mm in diameter and a magnet of NdFeB 50 mm in diameter, and a levitation force of 260 kN/m 2 (= 2.65 kgf/cm 2) for a superconductor 46.5 mm in diameter and a magnet of PrFeBCu 36 mm in diameter. The former is α = 0.67 and the latter is α = 0.81.

Mechanical resonance characteristics of a high-T/sub c/ superconducting levitation system

This research deals with dynamic response of a permanent magnet freely levitated above an excited high-T/sub c/ superconductor. Evaluation of dynamic characteristics is required in mechanical design of high-T/sub c/ superconducting levitation systems. Their dynamics is coupled with type II superconducting phenomena. By a numerical approach based on some macroscopic models we evaluate mechanical resonance characteristics of a superconducting levitation system. Numerical results show some nonlinear properties and effect of the flux flow in type-II superconductors, which are observed in experiments or predicted by analyses.

Analysis of a high T/sub c/ superconducting levitation system with vibration isolation control

This paper presents a method for controlling vibrations of a levitated high Tc superconducting body subjected to base disturbances. To have the control forces, an actuator consisting of a permanent magnet with an electromagnet was presented. The analytical solution for calculating levitation forces due to the permanent magnet and the control currents in the electromagnet was obtained. The levitation forces obtained coincide with the previously published results. The equation of motion of the levitated body subjected to base disturbances under the control was presented. Nonlinear vibrations of the body were first discussed; then the method of vibration isolation control using the direct disturbance cancellation combining the velocity feedback control was investigated. Numerical calculations were carried out for the levitation forces, with respect to the levitated body subjected to harmonic or pulse base excitations. It was clarified that the present method Is valid for controlling nonlinear systems like the magnetically levitated superconducting body.

Sling launch of a mass using superconducting levitation

A sling concept is discussed in which a projectile could be slowly accelerated around a circular path to extremely high velocity (>10 km/s) in a closed evacuated cryogenic tube that guides it around the circular path. A high normal conductivity layer is maintained on the inner surface of the guide tube, and a launch package with superconducting magnets is levitated in the tube so that EM drag is minimized and it moves in a nearly frictionless state. An accelerating coriolis force is then experienced inside the tube by driving a smooth low-speed displacement motion of the entire accelerator tube using rotating machinery distributed outside the closed tube around the circular path. The projectile accelerates under a force proportional to its mass and in a manner equivalent to sliding down an inclined plane of very small angle in a gravitational field of strength increasing as the square of the projectile velocity. This accelerating wave can be programmed to travel around the accelerator at extremely high speed. The kinetic energy invested in moving the circular guide tube is small compared with that in the projectile, although the tube momentum is dominant. Future applications depend on advances in the technology of strong superconducting levitation, but could range from hypervelocity impact research using small masses to the launch of large masses (tons) into space from the surface of the earth or moon.

Proposal and FEM analysis of superconductive magnetic gradient levitation

A magnetic levitation system that enables a stable levitation even at a standstill without active control has been studied by numerical analysis of electromagnetic field. The new superconductive magnetic levitation system consists of superconducting coils and iron rails, and its principle of levitation is based on a magnetic gradient in space, which is obtained by the flux-conservation characteristic of superconducting coils. A two-dimensional FEM program was used for analysis of electromagnetic force characteristics in a two-dimensional plane and the distribution of coil current. These results show the two-dimensional stability of the system.

Magnetic levitation using high-temperature superconductors: a materials perspective

The relationships between system parameters and material properties for a superconducting levitation (or suspension) system are investigated. A superconducting levitation measurement system, constructed to produce 5-T uniform magnetic field and approximately 1-T/cm uniform gradient in static mode, was used to measure the levitation of high-temperature superconductors. Up to 0.5 T/cm of the gradient field may also be pulsed with switching time approximately 0.1 s which was designed to perturb freely levitated superconductors in dynamic measurements. The displacement of the levitated sample was monitored using phase-sensitive inductive techniques which provided the magnitude of a magnetic force. The control of temperature and magnetic field, as well as the data acquisition, was done through an IEEE-488 interface and a 9- mu s analog-to-digital converter (ADC) using an 80386-based personal computer. The measurements and the theoretical analysis are compared. >

Estimation of Uncertainties Caused by Elastic Deformations in a Superconducting Levitation System

A method for estimation of the uncertainties caused by elastic deformations in a superconducting levitation electromechanical system is proposed. For the VNIIM system, with a monolithic supporting coil, these uncertainties are estimated to be 1 to 3 parts in 108.

A Study of an Absolute Determination of the Magnetic Flux Quantum Using a Superconducting Levitation System

A study on a new method of determining the magnetic flux quantum φ0 possibly at subppm level using a superconducting levitation system is described with some data from a preliminary experiment. The method employs a superconducting levitation system to substitute the gravitational potential energy of the floating body for the magnetic energy. The estimation of the expected accuracy and methods of improving the experiment are discussed.

A proposed design for multishell cryogenic laser fusion targets using superconducting levitation

A method is described for using the diamagnetism of superconductors to levitate a permanently magnetized fuel pellet within a spherical superconducting shell in a multishell cryogenic laser fusion target. A general expression is derived for the magnetic force on the fuel pellet as a function of its displacement from the center of the outer shell, and is used to calculate the equilibrium displacement due to gravity in a typical case. For a PtCo inner shell with a radius of 50 μm and a thickness of 1 μm, within a superconducting outer shell with a radius of 100 μm, the maximum displacement is 0.54 μm.

Characteristics of inductive magnetic levitation system with monopolar train loops

Pneumatic and magnetic levitation systems for ultraspeed (500 km/h) trains are now being studied intensively in many countries. This paper analyzes the behavior of a monopolar vehicular coil-type superconducting levitation system by the steady-state periodic solution method and shows that this system behaves in the same way as the conventional system as regards lift force, drag force and lift-to-drag ratio. It also shows that the magnetic force is always positive and sufficiently strong (larger than a damping time constant of 1 sec).