Bulk high-Tc Superconductors Research Articles

Emergent high-temperature superconductivity at interfaces

Abstract

Modeling of High-Tc Superconducting Bulk using Different Jc–T Relationships over Dynamic Permanent Magnet Guideway

The linear temperature dependence of critical current density Jc∝((Tc-T)/(Tc-T0)) and the nonlinear functions of Jc∝(1-(T/Tc)2)α with the exponent α equal to 1, 3/2, and 2 are used to calculate the dynamic levitation force, the temperature distribution, and the current density distribution of the high-temperature superconducting (HTS) YBaCuO bulk over a permanent magnetic guideway (PMG). The calculations were based on the H-formulation and E–J power law. The model of the HTS bulk and the PMG has been built as a geometric entity by finite element software. To simulate the magnetic field fluctuation caused by the PMG arrangement irregularity, a small amplitude vibration in the vertical direction is applied to the PMG during the calculations. Both the low vibration frequency of 2 Hz and the high vibration frequency of 60 Hz are analyzed as the representative converted linear speeds of 34 km/h and 1018 km/h for magnetic levitation (Maglev) application. We compared the electromagnetic-thermo-force modeling with the experiments and the previous model without considering the thermal effect. The levitation force computed by the Jc–T relationship, in which Jc is proportional to (1-(T/Tc)2)2, is found to be in best agreement with the experimental data under quasi-static conditions. This work can provide a reference for the HTS electromagnetic-thermal-force coupling reproduction method of HTS Maglev at high speed.

One-dimensional Stress Evaluation of a Ring Bulk HTS with Shrinkage Fit by an Iron Ring

The stress distributions of a ring bulk high-Tc superconductor are studied in the one-dimensional numerical analysis. Boundary condition is derivated under shrinkage fit by an iron ring. Convergences of the solutions are compared with the simple iteration method and the successive approximation method. Maximum hoop stresses are evaluated during the field-cooled magnetization. Differences of the solutions are also discussed between the present and the previous boundary conditions.

Maximum Hoop Stress Evaluation of a Hollow Cylindrical Bulk Superconductor in Field-Cooled Magnetization

Stresses are induced in a bulk high-Tc superconductor (HTS) by field-cooled magnetization. The stress distributions of a hollow cylindrical bulk HTS are numerically studied in the axisymmetric three-dimensional analysis. Shielding current distributions are obtained through a macroscopic numerical simulation with the Maxwell equations and the critical state model. Stress distributions are obtained by using the finite-difference method and iterative calculations. Maximum hoop stress during the field-cooled magnetization is discussed for open and fixed boundary conditions.

Effect of Pre-magnetization on Quasi-static Force Characteristics in a Space Superconducting Interface Structure Adopting High T c Superconductors

Flux-pinned interaction between high Tc superconductors (HTSs) and an applied magnetic field provides a new, no-contact interface approach that can be used in docking and assembling process of space module systems. Unlike operations on the Earth, the magnetization of the HTS happens in orbit which differs from the traditional field cooling (FC) magnetization, and the additional field has to be used to magnetize the HTS in advance and make it produce a self-stable force in the interacting process with the interfacing magnet. This paper presents a type of superconducting interface structure configuration consisting of bulk HTSs, actuation electromagnets and interfacing magnets, and discusses the effects of different magnetization conditions on the quasi-static force interaction between the HTS and the interfacing magnet. Primary experiments show that the HTS after pre-magnetization can show self-stable force behavior, which often happens in the traditional FC magnetization, and the self-stable force is further enhanced with the increase of the pre-magnetizing current. Multi-pulse field magnetization after the pre-magnetization is also applied to raise the trapped field strength (BT) of the superconductor. The results show that BT is added with the increasing number of the pulsed field, and the corresponding self-stable force properties are also improved. Therefore, the pre-magnetization combined with the pulsed field magnetization can enhance the flux trapping in the HTS and bring more stable force for the superconducting interface structure.

Axisymmetric Three-Dimensional Stress Distribution in a Hollow Cylindrical Bulk Superconductor

In magnetization process by field cooling of a bulk high-Tc superconductor (HTS), stresses are induced by the Lorentz force between shielding currents and magnetic fields. Evaluation of the maximum stress during the magnetization is important from the viewpoint of the destruction of the bulk HTS. Stresses in a hollow cylindrical bulk HTS are numerically evaluated in the axisymmetric three-dimensional analysis. Shielding current distributions are obtained through a macroscopic numerical simulation with the Maxwell equations and the critical state model. Uniform trapped fields are discussed for piled bulk magnets. The stress distributions are obtained through numerical analysis with the finite-difference method. Maximum hoop stress is discussed for different boundary conditions of the bulk HTS.

Improvement of the rotational characteristics in the HTSC-permanent magnet hybrid bearing using ring shaped magnet

We have developed the hybrid magnetic bearing using permanent magnets and the high-Tc bulk superconductor (HTSC). Pinning force of the HTSC is used for the levitation and the guidance. Repulsive force of the permanent magnets is introduced to increase the load weight of the magnetic bearing. In this system, the stator side permanent magnet has the ring type structure so that both pinning force and repulsive force are used effectively.In this paper, influence of the hybrid system on dynamic characteristics of the rotor is studied. The rotor which is supported by the hybrid magnetic bearing is rotated. Then, vibration and the gradient angle of the rotor are measured until the rotor reaches to the end of the resonance state. Three dimensional numerical analysis of the flux which penetrates on the surface of the HTSC is undertaken. The relation between the dynamic characteristics and the flux is considered, and that of the hybrid system is compared with the non-hybrid one. In the hybrid system, the flux is changed by the influences of the stator side permanent magnet. Vibration and the gradient angle of the hybrid system are shown to be smaller than that of the non-hybrid one.

Magnetic Force Investigation of High-Tc Superconducting Bulk over Permanent Magnet Railway under Different Lateral Offsets with Experimental Methods

The magnetic levitation transportation system is one of the potential applications of high-Tc superconducting (HTS) maglev system. The prototype HTS magnetic levitation system is composed of one HTS bulk and a permanent magnet railway (PMR). The maglev transportation system performance is influenced by the maximum levitation force, the maximum guidance force and the maximum of external applied magnetic flux density. The applied magnetic field distribution also needs to be considered carefully. In the paper, the magnetic levitation force of cylindrical HTS bulk over PMR is experimentally studied. During the experiment, symmetrical PMR and Halbach PMR are used separately. The levitation force-gap loops of different lateral offset of the HTS bulk above PMRs are obtained experimentally. The results show that the HTS bulk levitation performance is tightly relative to the external applied magnetic field distribution. The maximum magnetic levitation forces of HTS bulk above symmetrical PMR decrease linearly with the lateral offset increasing. When the lateral offset changes from 0 mm to 25 mm, the maximum magnetic levitation forces of HTS bulk above Halbach PMR increase with the lateral offset increasing. When the lateral offset exceeds the center of the Halbach PMR by 25 mm, the maximum force decreases rapidly with the increase of the lateral offset of the bulk sample.

Stress Evaluation in a Bulk High Tc Superconductor with Anisotropic Poisson's Ratio

Abstract In magnetization process by field cooling of a bulk high-Tc superconductor (HTS), stresses are induced by the Lorentz force between shielding currents and magnetic fields. Stresses in a cylindrical bulk HTS are numerically evaluated in the axisymmetric three-dimensional analysis. Shielding current distributions are obtained through a macroscopic numerical simulation with the Maxwell equations and the critical state model. The stress distributions are obtained through numerical analysis with the finite- difference method. Maximum stresses are discussed for the case with anisotropic Poisson's ratio of the bulk HTS.

Remagnetization effects due to lateral displacement above a PMG on bulk HTS magnet

For a high-Tc superconducting (HTS) maglev system with large force requirements, the use of magnetized bulk high-Tc superconductor magnets (MBSCMs) is a good candidate because of its strong flux pinning ability and corresponding high trapped flux. Different from the rare-earth permanent magnet (PM), the trapped flux of a MBSCM is sustained by the supercurrent produced by a magnetizing process, so the trapped flux is sensitive to variations of the supercurrent. The lateral displacement of a MBSCM above a PM guideway (PMG) will provide disturbance of the applied field and then alter the supercurrent as a process of remagnetization. Different magnetization histories will bring different remagnetization characteristics and consequently diverse levitation performances for a MBSCM during the lateral displacements. When the MBSCMs are applied into the HTS maglev system, the influence of lateral displacements on levitation performance should be taken into consideration. This article investigates the remagnetization characteristics of a MBSCM when it is subject to the lateral displacements above a PMG with different trapped magnetic flux and opposite magnetization polarities. Relevant analyses about the internal supercurrent configuration based on the critical state model are also included to better understand the remagnetization characteristic of a MBSCM.

Feasibility of introducing ferromagnetic materials to onboard bulk high-Tc superconductors to enhance the performance of present maglev systems

Performance improvement is a long-term research task for the promotion of practical application of promising high-temperature superconducting (HTS) magnetic levitation (maglev) vehicle technologies. We studied the feasibility to enhance the performance of present HTS Maglev systems by introducing ferromagnetic materials to onboard bulk superconductors. The principle here is to make use of the high magnetic permeability of ferromagnetic materials to alter the flux distribution of the permanent magnet guideway for the enhancement of magnetic field density at the position of the bulk superconductors. Ferromagnetic iron plates were added to the upper surface of bulk superconductors and their geometric and positioning effects on the maglev performance were investigated experimentally. Results show that the guidance performance (stability) was enhanced greatly for a particular setup when compared to the present maglev system which is helpful in the application where large guidance forces are needed such as maglev tracks with high degrees of curves.

Pore structure dependence with the sintering time for dense ceramic bulk YBa2Cu3Oy

Technological applications of bulk high-TC superconductors, in particular of YBa2Cu3Oy, require polycrystalline materials with improved physical properties which strongly depend on the presence of pores and their characteristics. In this work we have studied the pore structure and their principal features in dense YBa2Cu3Oy samples prepared with different sintered times. The samples were prepared through a classic solid state reaction method. The critical temperatures of the samples were measured by using zero field cooling magnetization. The pore structure and their features were studied through N2 sorption measurements. Our experimental results show that the principal characteristics of the pore structure depend on the sintering time. In particular, samples sintered during 24h show a higher porosity and external surface area, as also a more heterogeneous pore distribution slightly shifted to the low pore widths region, when compared to other samples sintered by using different times. Our work shows the importance of the sintering conditions regarding the controlling of the porous character of bulk YBCO superconductors.

Low-Temperature Operation of a Bulk HTSC Staggered Array Undulator

A use of bulk high-temperature superconductors (HTSs) for an undulator is attractive since a high magnetic field can be generated at low-temperatures. While potential for generation of the high magnetic field is high, in-situ magnetization of the bulk HTSs for periodic field generation is challenging issue. Recently, we proposed a new type of undulator using bulk high-Tc superconductors (HTS) and a solenoid magnet. The undulator, named Bulk HTSC staggered array undulator (Bulk HTSC SAU), consists of a stacked array of bulk HTSs and copper insulators and a solenoid magnet. A proof of principle experiment at 77 K using liquid nitrogen has been carried out. The estimated performance at about 30 K was estimated using results of property measurements for the HTS used for the Bulk HTSC SAU. The expected undulator peak field reaches to 1.08 T for undulator period length of 9.9 mm for the undulator gap of 4.0 mm. This performance is about 2 times higher than that of existing technologies.

Numerical evaluation of field profile in an undulator with bulk HTS

Application of a bulk high-Tc superconductor (HTS) to a permanent magnet undulator is numerically evaluated using macroscopic numerical simulation based on the critical state model. Shielding currents are induced by field-cooled magnetization with increasing of the gap length between magnets of the undulator. A hole of the HTS ring is treated as low conductivity region. Magnetic field at the center of the undulator is compared for cases with and without the bulk HTS. Numerical results agree well with the experimental results. Shielding field of the HTS ring is also numerically evaluated and discussed with experimental results.

Ultra-low DC Magnetic Field Detection Using Ceramic Superconductors

In the present study, the linear behavior of the second harmonic signal generated by application of very low DC magnetic fields to the polycrystalline bulk high-Tc superconductors has been examined. The amplitude of AC field, Hac, intergranular first critical field, H1cJ, and minimum field required for the magnetization of specimen as a whole, H∗, were determined and a special coil design has been presented. The results reveal that the second harmonic signal varies linearly with the applied DC field in the −0.1 Oe to 0.1 Oe range. Additionally, detection of ultra-low DC fields as small as 5 nT has been achieved. Repeatability and reproducibility tests were performed and the resultant data have been found to be consistent. In the light of our study, a commercial magnetometer can be produced to be utilized in successful detection of very low magnetic fields.

Influence of lateral displacement on the levitation performance of a magnetized bulk high-Tc superconductor magnet

Compared with the permanent magnet, the magnetized bulk high-Tc superconductor magnet (MBSCM) can trap higher magnetic field due to its strong flux pinning ability, so it is a good candidate to improve the levitation performance of high-Tc superconductive (HTS) maglev system. The trapped magnetic flux of a MBSCM is sustained by the inductive superconducting current produced by the magnetizing process and is susceptible to the current intensity as well as configuration. In the HTS maglev system, the lateral displacement is an important process to change the superconducting current within a MBSCM and then affects its levitation performance, which is essential for the traffic ability in curve-way, the loading capacity of lateral impact and so on. The research about influence of lateral displacement on the levitation performance of MBSCM is necessary when MBSCM is applied on the HTS maglev vehicle. The experimental investigations about the influence of lateral displacement on the levitation performance of a MBSCM with different trapped fluxes and applied fields are processed in this article. The analyses and conclusions of this article are useful for the practical application of MBSCM in HTS maglev system.

Rotational characteristics in the resonance state of the HTSC-permanent magnet hybrid magnetic bearing

The hybrid magnetic bearing using permanent magnets and the high-Tc bulk superconductor (HTSC) has been developed. Repulsive force of the permanent magnet is introduced to increase the load weight of the magnetic bearing. Effect of the hybrid system has been shown.In this paper, influence of the hybrid system on the dynamic characteristics of the rotor is studied. The rotational characteristics in the mechanical resonance state are studied, and the equivalent magnetic spring coefficient is estimated from the experimental results of the load weight. The resonance frequency is measured by the rotation experiments. The rotor achieves stable levitation even in the resonance state. In the hybrid system, effect of the pinning force becomes smaller than that of the lateral force generated by the repulsive force between the two permanent magnets at the smaller air gap. Thus influence of the lateral vibration and the gradient angle in the resonance state becomes larger at a smaller air gap. The equivalent magnetic spring coefficient becomes also small, and the resonance frequency becomes small in the hybrid bearing system.

Conceptual design of a novel insertion device using bulk superconducting magnet

An undulator or a wiggler with a strong magnetic field will play an important role in future synchrotron light sources, free electron lasers, and linear colliders. We proposed the bulk high critical temperature superconductor staggered array undulator (Bulk HTSC SAU) in order to generate a strong periodic field. The Bulk HTSC SAU consists of stacked bulk high-Tc superconductors (HTSs) and a solenoid magnet which is used to magnetize the bulk HTSs. A periodic magnetic field was produced and controlled using a prototype of the Bulk HTSC SAU using 11 pairs of REBaCuO bulk HTSs at 77K. The expected performance at low temperatures around 20K is calculated using a loop current model.

High-Performance Permanent Magnet Railway Design Consideration of Magnetic Stiffness Parameters of YBCO Bulk Arrays

The monopole permanent magnet railway (PMR) is used in the present high-Tc superconducting (HTS) maglev vehicle system. In order to improve the performance of the present maglev vehicle system, many studies have been done to optimize the maglev system. Stiffness is one of the important parameters for maglev vehicle system design. In this article, measurement of the vertical and lateral magnetic force stiffness of HTS bulk arrays above monopole PMR and double-pole PMR are measured. Comparing the experimental results, it is found that the magnetic force stiffness of bulk arrays above double-pole PMR is better than that of monopole PMR. The experimental results show that the running stability of HTS maglev vehicle system using double-pole PMR is much better than that of using monopole PMR.

Levitation performance of the magnetized bulk high- Tc superconducting magnet with different trapped fields

To a high- T c superconducting (HTS) maglev system which needs large levitation force density, the magnetized bulk high- T c superconductor (HTSC) magnet is a good candidate because it can supply additional repulsive or attractive force above a permanent magnet guideway (PMG). Because the induced supercurrent within a magnetized bulk HTSC is the key parameter for the levitation performance, and it is sensitive to the magnetizing process and field, so the magnetized bulk HTSC magnets with different magnetizing processes had various levitation performances, not only the force magnitude, but also its force relaxation characteristics. Furthermore, the distribution and configuration of the induced supercurrent are also important factor to decide the levitation performance, especially the force relaxation characteristics. This article experimentally investigates the influences of different magnetizing processes and trapped fields on the levitation performance of a magnetized bulk HTSC magnet with smaller size than the magnetic inter-pole distance of PMG, and the obtained results are qualitatively analyzed by the Critical State Model. The test results and analyses of this article are useful for the suitable choice and optimal design of magnetized bulk HTSC magnets.