Applications Of high-Tc Superconductors Research Articles

Attractive interaction between superconducting vortices in tilted magnetic fields

Many practical applications of high Tc superconductors involve layered materials and magnetic fields applied on an arbitrary direction with respect to the layers. When the anisotropy is very large, Cooper pair currents can circulate either within or perpendicular to the layers. Thus, tilted magnetic fields lead to intertwined lattices of Josephson and Abrikosov vortices, with quantized circulation across and within layers, respectively. Transport in such intertwined lattices has been studied in detail, but direct observation and manipulation of vortices remains challenging. Here we present magnetic force microscopy experiments in tilted magnetic fields in the extremely quasi-two dimensional superconductor Bi2Sr2CaCu2O8. We trigger Abrikosov vortex motion in between Josephson vortices, and find that Josephson vortices in different layers can be brought on top of each other. Our measurements suggest that intertwined lattices in tilted magnetic fields can be intrinsically easy to manipulate thanks to the mutual interaction between Abrikosov and Josephson vortices.

Dynamic simulations of actual superconducting maglev systems considering thermal and rotational effects

Recently, the application of high-Tc superconductors with longitudinal geometry to linear bearings and transportation devices has reached a higher stage of development. For these maglev systems, static stability has already been established; but dynamic stability is still under investigation, since these systems have multiple degrees of freedom and their dynamics are coupled with intricate superconducting phenomena. In this paper, in terms of Newton’s second law, the thermal diffusion equation, and Maxwell’s equations together with a nonlinear power-law constitutive relation, we build a two-dimensional thermal–electromagnetic coupling model to study the dynamics of actual maglev systems composed of a superconductor and a guideway formed by conventional and Halbach arrays of permanent magnets. We assume that the zero-field-cooled superconductor slowly descends to a working height and then its dynamic motion is triggered by an external disturbance or excitation. The results show that when the superconductor has a disturbance-induced initial translational or angular velocity at the working position, vibration and drift phenomena occur simultaneously in the lateral, vertical and rotational directions, and the local temperature rise will aggravate the center of the drift of vibration but will shorten the levitation stabilization time. Lowering the ambient temperature is effective at alleviating the levitation drift. However, a balance between the levitation force and lateral stability should be noted because an excessively low ambient temperature may lead to instability. Additionally, a resonance phenomenon will occur under an external excitation if its frequency is too close to the system’s resonance frequency, which causes a dramatic rise in local temperature and a further large drift for the center of vibration.

Effect Y substitution on the microstructure, transport and magnetic proprieties of Bi2Sr2Ca1Cu2O8+δ superconducting ceramics

AbstractIn high Tc superconductors (HTSC) the activation energy gives information about the pinning properties of a sample under applied magnetic field. Pinning of vortices determines the critical current density Jc which is of great importance for practical applications of HTSC. Instead of magnetic measurements, the activation energy may be calculated from resistivity measurements realized under magnetic field. This kind of measurement has been made in this work for yttrium doped samples of Bi2Sr2CaCu2O8+d (Bi-2212) for different values of applied magnetic field. Samples of Bi2Sr2Ca1-xYxCu2O8+d (x = 0, 0.025, 0.1, 0.25) were prepared by a sol-gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive analysis of X-ray. The measurements of resistivity were made using a classical four probe method and DC current. The magnetic field was applied with a constant amplitude of 0 T, 1 T, 2 T and 3 T. The obtained results show that the activation energy decreases with introduction of yttrium, but has a relative maximum when x is equal 0.1. The decrease of the activation energy is explained by the granular nature of the samples which promotes 3D transition to 2D of the vortex lattice.

Microstructural and magnetic analysis of a superconducting foam and comparison with IG-processed bulk samples

YBa2Cu3Oy (YBCO) foam samples show an open, porous foam structure, which may have benefits for many applications of high-Tc superconductors. As the basic material of these foams is a pseudo-single crystalline material with the directional growth initiated by a seed crystal similar to standard melt-textured samples, the achieved texture of the YBCO is a very important parameter. We analyzed the local texture and grain orientation of the individual struts forming the foam by means of atomic force microscopy and electron backscatter diffraction (EBSD). Furthermore, the magnetic properties of a foam strut are evaluated by means of SQUID measurements, from which the flux pinning forces were determined. A scaling of the pinning forces in the temperature range between 60 K and 85 K was performed. These data and the details of the microstructure are compared to IG-processed, bulk material.

Analysis of the microstructure of superconducting YBCO foams by means of AFM and EBSD

YBa2Cu3O y (YBCO) foam samples show an open, porous foam structure, which may have benefits for many applications of high-Tc superconductors. As the basic material of these foams is a pseudo-single crystalline material with the directional growth initiated by a seed crystal similar to standard melt-textured samples, the texture of YBCO is a very important parameter. Therefore, we analysed the local texture and grain orientation of the individual struts forming the foam by means of atomic force microscopy (AFM) and electron backscatter diffraction (EBSD). Due to the processing route starting with Y2BaCuO5 (211), a two-phase analysis must be performed, so a high surface quality is necessary to enable an automated EBSD scan. Good quality Kikuchi patterns were obtained from both the YBCO and 211 phases. We found an inhomogeneous distribution of the residual 211 particles, which are mainly randomly oriented and have sizes ranging between 200 nm and 15 μm. In contrast to this, the YBCO matrix shows a dominating orientation with cracks with a typical distance of 1–10 μm. Furthermore, the analysis of strut cross-sections reveals that the entire strut is converted to the YBCO phase.

Suspension of a YBCO Tape and its Numerical Evaluation

Superconducting electric power transmission is a useful power application of high Tc superconductors. In addition to the conventional Bi-system tape material, YBCO tape material reaches to the level of a practical use. The YBCO tape material has high critical current density and strong pinning force. In the paper, a field-cooled YBCO tape is suspended under a permanent magnet to confirm the strong pinning force. The experimental results are numerically evaluated with the flux pinning model by using Maxwell stress. The total pinning force is roughly discussed from experimental suspension limits.

Challenge to Functional, Efficient, and Compact Accelerator Systems using High <i>T</i><sub>c</sub> Superconductors

Application of high Tc superconductors to accelerator magnets provides the following benefits. It reduces power consumption compared to copper magnets, it allows simple operation and less governmental regulation compared to low Tc superconductors because of the applicability of cryocoolers, and it is potentially more stable thermally, when operated at high temperatures where the specific heats of materials are large. An R&D project focusing on fundamental technologies for accelerator magnets using coated conductors is in progress, funded by the Japan Science and Technology Agency from January, 2010. Stage I of the project was completed successfully in March, 2012, and the project moved to the four-year Stage II in April, 2012. We aim to realize application of high Tc superconductors to magnets of strong-focusing accelerators for carbon cancer therapy or accelerator-driven subcritical reactors (ADSR). In Stage I, we conceptually designed a couple of fixed-field alternating gradient (FFAG) accelerators for carbon cancer therapy and for ADSR as well as a beam transport line for a carbon cancer therapy facility. Based on the conceptual designs of accelerators, coil-dominated magnets and iron-dominated magnets wound with coated conductors were designed. The required winding technologies were clarified through designing these magnets, and the R&D of winding technologies for coils with three-dimensional shape and those with negative bend have been carried out. The influence of the magnetization of coated conductors on the field quality of magnets was studied experimentally. The influence of the neutron radiation on the conductivity of aluminum and that of copper was also studied.

Effect of addition of soft magnetic alloy particles on the flux trapping in Gd123 bulk superconductors

Pinning stability and the introduction of magnetic flux pinning is an essential problem in applications of high-Tc superconductors. Study on the role of addition of a variety of metal oxides into GdBa2Cu3O7−δ (Gd123) bulk superconductors was carried out. We found that the addition of 0.05 wt. % of soft magnetic alloy particles Fe-Cu-Nb-Si-Cr-B (Fe-B) into the Gd123 contributes to the enhancement of the critical current density (Jc) under a wide range of applied magnetic fields up to 3 T. The Fe-B particles refined less than 10 μm by ball milling indicate no remarkable contribution on the Jc under the magnetic field. The reduction of the Ba content resulted in the appearance of a peak of Jc which has been observed in the Gd/Ba solid solution with rich Ba content. These results let us discriminate the effect of the magnetic particles from other conventional flux pinning mechanism. The peak of Jc under magnetic field was not only observed in the part along the c-axis under the seed of the sample but also in the growth sector around the periphery of the Gd123 bulk with Fe-B addition. It indicates that the magnetic particles inclusions play an important role on the homogeneous enhancement of Jc and the high flux pinning performance.

Novel magnetic sensors using highTc superconductors

We propose a novel magnetic sensor to apply a new phenomenon in highTc superconductors of strongly anisotropic materials. We have found periodic oscillations in theflux-flow resistance of Josephson vortices in intrinsic Josephson junctions of single crystallineBi2Sr2CaCu2O8+y, fabricated by using a focused ion beam. The periodic oscillations in the flux-flowresistance have been observed at higher magnetic fields than 70 kOe at low temperatures.The period depends only on the junction width perpendicular to the magnetic fields andthe current, independent of temperature and magnetic field. The detailed analyses of theoscillations show that the characteristics of the flux-flow device can be applied asmagnetic sensors to detect an absolute magnetic field and to measure the fieldprecisely to an accuracy in the 1 mOe range, even under magnetic fields as high as70 kOe. We believe that this kind of sensor opens up new applications of highTc superconductors.

Selected problems in power applications of high Tc superconductors

Two important problems connected with power applications of BSCCO tapes are discussed: (i) the problem of developing prototypes when the tape properties are changing, and (ii) the problem of flux pinning in intrinsic BSCCO. An overview of the different projects on superconducting power cables is given.

Generation of coherent electromagnetic radiation by superconducting films at liquid-nitrogen temperatures

Generation of coherent electromagnetic radiation by GdBa2Cu3O7−x superconducting films is observed in the frequency range 1–10 MHz at the temperature of boiling liquid nitrogen. The generation is caused by the feedback synchronization of the jumps of Abrikosov vortices produced by a low-frequency external magnetic field. This offers new possibilities for the application of high-T c superconductors in superconducting electronics.

Josephson plasma observed in underdoped (110) YBa2Cu3O7−δ films

(110) oriented YBa2Cu3O7−δ thin films have been epitaxially grown on vicinal (110)SrTiO3 substrates by pulsed-laser deposition. Films with different oxygen deficiencies were obtained by annealing under various oxygen ambient. These films have very smooth surface and with their c axis aligned in one direction in the substrate plane. Electronic transport and polarized far-infrared reflectivity measurements reveal the unique features of the c-axis charge dynamics. A c-axis far-infrared reflectivity edge associated with the Josephson plasma in the superconducting state is observed. Our results demonstrate the potential usage of (110) thin films for the investigation of intrinsic interlayer charge dynamics as well as device application of high Tc superconductors.

Recent advances in the R&D of high- Tc superconductors for large-scale applications in China

The spectacular discoveries of high- T c superconductors (HTS) since 1986 have excited a great deal of application research interest. This paper will review the recent advances of the large-scale applications of HTS in China, including power cables, current leads, fault current limiters (FCL), MRI magnet, as well as bulk YBCO-based applications such as permanent magnets and bearings, etc.

Fundamental characteristic estimation based on finite element method for magnetic shielding type superconducting fault current limiter

The superconducting fault current limiter is expected to be the first application of high-Tc superconductors (HTSs) in power systems. To develop a magnetic shielding-type superconductor fault current limiter, we have carried out some fundamental experiments on the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into Bi-2223 cylinders are shown. An ac magnetic field is applied to the sample by a primary winding (copper coil) excited by ac triangular- and sinusoidal-waveform currents in the frequency range from 0.1 Hz to 100 Hz. We also developed a finite element method computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage–current (E–J) characteristic are compared with experiments. Next we carried out a current-limiting test with a small limiter model, and the developed finite element method computer program successfully simulated the electromagnetic behavior in current-limiting operation. © 2000 Scripta Technica, Electr Eng Jpn, 134(1): 17–27, 2001

有限要素法による磁気遮へい型超電導限流器の基礎特性評価

The superconducting fault current limiter is expected to be the first application of high-Tc superconductors (HTSs) in power systems. To develop a magnetic shielding-type superconductor fault current limiter, we have carried out some fundamental experiments on the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into Bi-2223 cylinders are shown. An ac magnetic field is applied to the sample by a primary winding (copper coil) excited by ac triangular- and sinusoidal-waveform currents in the frequency range from 0.1 Hz to 100 Hz. We also developed a finite element method computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage–current (E–J) characteristic are compared with experiments. Next we carried out a current-limiting test with a small limiter model, and the developed finite element method computer program successfully simulated the electromagnetic behavior in current-limiting operation. © 2000 Scripta Technica, Electr Eng Jpn, 134(1): 17–27, 2001

Review of Applications of High-Temperature Superconductors

Since the discovery of high-Tc superconductor oxides in 1986, much research and development have been carried out, and much progress has been made. In the last ten years our efforts have been devoted to the development of materials technologies for these difficult materials, and remarkable progress has been made. This is a great contribution not only for application but also for fundamental research on high-Tc superconductors. In this paper, we will present a review of applications of high-Tc superconductors discovered in the last ten years. At present, it can be said that we are in the transition period from the period of growth to the period of specialization, looking for future applications of high-Tc superconductivity.

Properties of superconducting Bi-2223 tubular current leads

The superconducting current leads to conventional or high Tc superconducting magnets operating at low temperatures are one of the earliest applications of high Tc superconductors. Optimization of the preparation procedure of the BiPbSrCaCuO ceramic superconductor (2223 phase) with respect to texturing and critical current density made possible fabrication of tubular superconducting current leads of relatively thin wall and enhanced texture. They exhibit the self-field critical current density of about 1000 A/cm2 at 77 K. The basic physical properties necessary for proper design of the current leads, i.e. dependencies of the critical current on the external magnetic field, the self-field critical current density on the temperature and the thermal conductivity on the temperature are shown in the work. The use of protective metal cases protects the superconductor ceramic tubes against a damage caused by thermal shocks and overcurrents, as well.

Low-critical-current applications of high-Tc superconductors

The short-term large-scale applications of high-Tc superconductors are not limited only to the high critical-current ones (electrotechnical, levitation). Several low-critical-current applications are possible. Some, which already have industrial potential, are reviewed in this paper: magnetic shielding, thermal shielding and magnet current leads, all making use of extended thick ( > 50 μm) films. The state-of-the-art of the results is briefly summarized.

Prospects for applications of high-Tc superconductors

In ten years of short history in research and developments of high-Tc superconductors, the material technology on these difficult materials made quick and big progress. And the directions of research and developments in wide range of applications are becoming clear. At present these directions are classified into three categories: (a) Developments of high quality superconducting wires and tapes. (b) Developments of large bulk superconductors having high critical currents. (c) Developments of new superconducting electronic devices. All this application research must be based on how we can control those materials in quality and functions. After describing problems in material technologies, prospects for applications are discussed.

Stability and AC losses in HTSC/Ag multifilamentary strands

Large-scale applications of high-Tc superconductors (HTSCs) stem not only from their obviously high Tc values which offer the possibility of operation in liquid hydrogen, liquid helium as well as refrigerated gases, but also from their high Hc2 values when high operating temperature is not the primary consideration. The cryophysical properties central to dynamically and adiabatically stable conductor design are the temperature-dependent thermal conductivity and specific heat, respectively. Based on these data and the field and temperature dependence of Jc for melt-processed YBCO, calculations are presented of the limiting filament diameters for flux-jump-stable operation (at 4 and 77 K, and 0 and 5 T) of a hypothetical YBCO/Ag composite strand. A calculation is also presented of the field-amplitude dependence of 50 Hz hysteretic and eddy current losses of a model multifilamentary (MF) HTSC/Ag composite strand. It is demonstrated that the eddy current loss of a fully coupled MF strand is considerably larger than the hysteretic loss of the equivalent monocore. The roles of filamentarization and twisting in MF HTSC/Ag strands are discussed. The results of an experimental AC loss study of a series of MF Bi:2212/Ag strands are also presented. Various features of the AC loss are interpreted in terms of: (i) flux-creep enhanced field sweep rate dependence, (ii) bridging and “current-sausaging” enhanced effective filament diameter, deff; and (iii) bridging-induced sample-length dependence of the per-cycle AC loss and its modification by extreme current sausaging also referred to as ‘minor current loops’.