2PO8-20 Increase in Levitation Force by Replacing Ferromagnets with Field Cooled YBa₂Cu₃O_y Trapped Field Magnets

W. Hennig, D. Parks, R.-P. Sawh, and R. Weinstein, Department of Physics and TCSUH, University of Houston, Houston, TX 77204-5506, USA

Presenting Author: W. Hennig

YBa₂Cu₃O_y HTS, cooled in a field of 2.3T, are used in place of permanent ferromagnets (PM) as the source of field in levitation. The HTS, cooled in a field greater than their maximum trapped field (B_t,max), are fully saturated (fc_sat). They produce fields equal to B_t,max (up to 1.6T in this work). Since commonly used PM produce only ~0.5T, replacing the PM in levitation systems with such HTS trapped field magnets, TFM, significantly increases the magnetic field and thus the levitation force, F_L.

The TFM is opposed by a second HTS which is (1) cooled in zero field, (2) fc_sat, or (3) cooled adjacent to the TFM. F_L and its dependence on B_t,max is investigated. Lateral forces are used to estimate the stability of the configurations.

Compared to common levitation systems with PM, F_L increases by a factor of 4-10 with TFM as the source of field; up to 393N (125N/cm²) are obtained. F_L(B_t,max) is normalized to a common curve for data sets with different TFM. The common curve is calculated from the average magnetization of the HTS. Single-sample configurations, depending on the cooling conditions, have limited stability. However, arrangements of several samples are shown to improve stability.

2PO8-21 Drag Torque and Power Loss in High T_c Superconductor Magnet Bearings with Multi-piece Ring Magnets or Superconductors.

Yevgeniy V. Postrekhin, Hong Ye, Ki Bui Ma, and Wei-Kan Chu, Texas Center for Superconductivity University of Houston, Houston TX 77204

Presenting Author: K.B. Ma

In order for a superconductor magnet levitation bearing to rotate freely, the magnetic field from the magnet must be axisymmetric about the axis of rotation. In contrast, the shape of the superconductor need not be axisymmetric. This allows us to make a large ring of high temperature superconductor out of smaller pieces in the fabrication of superconductor magnet bearings. Nevertheless, permanent magnets typically have a few percent fluctuation of the magnetic field around its circumference that leads to a small power loss in the bearings made from these magnets. The problem then arises as to whether the substitution of a single large piece of superconductor by smaller pieces might contribute to additional power loss. We have investigated this by studying the drag torque experienced by multi-piece ring magnets as they turn above multi-piece rings of superconductors, and comparing with results from single pieces of similar sizes. We have coordinated the variation of the drag torque during a turn with the relative orientation of the magnet and superconductor pieces. We use the mean value of the drag torque over several turns as a measure of power loss and studied this as a function of speed and magnet/superconductor configuration.

2PO8-22 Force and Stiffness in a Superconductor Magnet Journal Bearing

Yevgeniy V. Postrekhin, Yong Zhang, Chong Wang, Ki Bui Ma, Quark Chen, and Wei-Kan Chu, Texas Center for Superconductivity, University of Houston, Houston TX 77204

Presenting Author: Y.V. Postrekhin

The purpose of a journal bearing is to provide a frictionless interface between a rotor and its stationary supports that confines the rotating axis of the rotor to designated position and direction. In addition, a journal bearing is required to provide balancing forces along the rotor axis in certain applications. Using superconductors and magnets, a journal bearing could consist of a permanent magnet cylinder in a superconductor ring, or a superconductor cylinder in a magnet ring. We have assembled superconductor magnet journal bearings of both configurations, and investigated the behavior of the axial force, and the axial and lateral stiffnesses that each can provide. We have put together numerical models of the interaction between the permanent magnet and the superconductor that is capable of describing these experimental results semi-quantitatively. Combining direct experimental measurements and using the numerical models proposed, we have studied the effect of changing the various dimensions of the components, material parameters such as the critical current density of the superconductor, and material quality such as the homogeneity of the superconductor samples.

2PO8-23 Bi-2212/Ag Tapes and Laminates: Bending and Joining Effects

A.Y. Ilyushechkin, T. Yamashita and P. Talbot, Advanced Ceramics Development, UniQuest6 Ltd., The University of Queensland, St. Lucia, Queensland 4072, Australia

Presenting Author: A.Y. Ilyushechkin

Superconducting composite Bi-2212/Ag tapes and laminates and their joints are fabricated by a combination of dip-coating and partial melt processing. The heat treated tapes have critical current (I_c) between 7 and 24 A, depending on tape thickness and number of Bi-2212 ceramic layers (for laminated tapes). Current transmission up to 100% has been achieved through the joints of single tapes and laminated tapes.

We have investigated different types of HTS joints of Bi-2212/Ag tapes and laminates and degradation of their transport properties during winding operations. It is found that the quality of joints depends on the laminate's composition and the joint configuration. From observations of laminates and their joints microstructure, possible factors of current losses are discussed.

Irreversible strain (e _irr) for laminated tapes and their joints has been determined and it has been found that degradation of I_c during tape bending is dependent upon the type of joint. From this information joint types can be selected for applicability for fabrications of HTS coils by "react-and-wind" or "wind-and-react" method.

2PO8-24 Review of the Fabrication of Superconducting Joints using Powder Metallurgy Method

Gan Liang, Dept. of Physics, Sam Houston State University, Huntsville, TX 77341

Presenting Author: G. Liang

High resolution NMR spectrometer magnets require the use of superconducting joints for splicing magnet coils. In recent years, we have developed various NbTi-NbTi, Nb₃Sn-NbTi, Nb₃Sn-Nb₃Sn, and HTS-LTS superconducting joints for various HTS and LTS wires/tapes using the powder mettallurgy (PM) method. In this paper, the joint fabrication process and test results are reviewed. Our results show that the PM joint fabrication technique can produce joint with extremely low electrical resistance, suitable for the construction of persistent mode high-field NMR spectrometer magnets and other applications.

2PO8-25 Bulk HTS Bi-2223 Bar Strong Current Performance and Applications

Jian X. Jin, Xue K. Fu, and Shi X. Dou, Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia

Presenting Author: J.X. Jin

A high temperature superconducting (HTS) Bi-2223 textured bulk bar with solid current terminals has been produced using hot-press techniques. High critical current has been achieved at 77 K, and therefore it can be ideally employed for strong current applications such as to form current lead and fault current limiter element. A sample produced has been measured to identify its practical performance related to large transport currents. The sample and its testing results will be introduced, and the sample will also be analyzed with regard to applications for current lead and fault current limiting element.

2PO8-26 Low resisitivity connection between YBCO superconductor and silver using dipping method

Susumu Seiki, Junya Maeda, Yuichi Nakamura, Teruo Izumi, and Yuh Shiohara, Superconductivity Research Laboratory(SRL), International Superconductivity Technology Center (ISTEC), 1-10-13, Shinonome, Koto-ku, Tokyo 135-0062, Japan

Presenting Author: S. Seiki

For practical applications of superconducting current leads and wires of REBCO superconductor, the low resistivity connection between the superconductive oxide and metals is required to supply a large current. In this work, YBa₂Cu₃O_x (Y123) superconducting rods prepared by the unidirectional solidification method were dipped into the molten silver in order to fabricate a metal contact on the surface of the superconductor. In the case of the dipping into the pure molten silver, a copper poor reacted layer was formed at the boundary between Y123 and silver metal, although the temperature of the molten silver was controlled lower than the decomposition temperature of the Y123 phase. This copper poor reacted layer is thought to be formed by the partial dissolution of Y123 into the pure molten silver. This phenomenon can be explained by the difference of chemical potential of copper element between Y123 matrix and silver melt. The formation of this reacted layer could be suppressed by means of addition of Y123 powder into the molten silver. Saturation of Y123 in the silver melt leads optimization of the concentration for suppression of dissolution. This method successfully realized the contact with the low resistivity of 10-12ƒ¶m2.

This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) as Collaborative Research and Development of Fundamental Technologies for Superconductivity Applications.

2PO8-29 Design and Evaluation of a High Temperature Superconducting Maglev System

Kris Vandenbroucke 1, Ari Zachas 1, Rupert J. Cruise 1, Charles F. Landy 1, Malcolm D. McCulloch 2, and Gary Barnes 2. 1 Department of Electrical Engineering, The University of Witwatersrand, Private Bag 3,Wits 2050, South Africa. 2 Department of Engineering Science, University of Oxford, United Kingdom.

Presenting Author: Kris Vandenbroucke

A High Temperature Superconducting (HTS) magnetic levitation system has been evaluated. The proposed system is a linear motor that generates the propulsion force, the suspension force and stabilization force from a single excitation source. The linear motor consists of a V-shaped linear motor primary winding and a secondary of 18 HTS pellets in a molded polystyrene container. A finite element model was employed to model the behaviour of machines made from HTS materials. The critical state model forms the basis of the method by governing the movement of the magnetic flux within the superconductor. This paper presents the results from the simulations showing that the maximum thrust and levitation forces generated by such a machine is a function of the critical current density, the applied magnetic field magnitude and the separation distance between the HTS pellets. The relation between these parameters which results in the most efficient secondary configuration has been deduced from simulations as well as the practical implementation of the linear motor. The motor runs asynchronously and can best be classed as a linear hysteresis motor.Measure-ments taken on the proposed system revealed a maximum levitation force of 14.2 N and a maximum thrust force of 1.3 N. The maximum levitation height obtained for the scale-model was 26 mm.