A magnetic drug delivery system (MDDS) has recently been developed enabling magnetic seeded drugs to be navigated around the diseased parts of the human body. To improve the magnetic drug delivery performance, a portable superconducting bulk magnet system with strong magnetic fields has also been developed. This magnet system primarily consists of small bulk high-temperature superconductors and a compact Stirling-cycle cryocooler. The materials used in the high-temperature superconductors are rare earth 123 single domain compounds (GdBaCuO). The main body of the magnet is 9.5 kg and 740 mm in length. In this study, a bulk magnet was successfully activated using field-cooling magnetization under a superconducting solenoid magnet. The magnetic flux densities at the surface of the vacuum chambers that contain the bulk magnets reached 5.07 T and 6.76 T under the static fields of 6 T and 10 T, respectively. We clarified that the magnetic gradient was approximately 10 T/m at a position 50 mm from the surface of the vacuum chambers. This operating bulk magnet system is portable and can be easily transported via car over long distances.
Two new approaches to fabricate Y123 melt-solidified bulks with excellent superconducting properties have been developed. One is a new method of crystal growth from a seed crystal with its c-axis parallel to the top surface, and the other is a high-temperature annealing process under a moderately reducing atmosphere after crystal growth. In the present study, the former method increased the area of high-Jc regions, and the latter enhanced Jc, particularly at positions far from the seed crystal at low temperatures through suppression of yttrium substitution for barium. The field-trapping property was also improved through introduction of a reductive annealing process prior to oxygen annealing at low temperatures.
A fusion reactor generates a lot of 14 MeV neutrons, some of which penetrate shielding blankets, stream out of ports and reach superconducting magnets. Some important studies were performed in the 1970s and a basic understanding of the mechanisms of neutron irradiation effect was established. Advances in the design concept of nuclear fusion reactors led to the need for consistent studies on the neutron irradiation effect of A-15 strands such as Nb3Sn and Nb3Al, which are strong candidates for fusion reactors. In the early 2000s, a progressive attempt to organize the collaborative research of universities and national institutes was started using a 14 MeV neutron source at Japan Atomic Energy Agency. This paper outlines the neutron irradiation issues related to superconducting magnets for fusion, and a brief history of research on the neutron irradiation effect is provided. In addition, experimental results regarding changes in the superconducting properties of Nb3Sn and Nb3Al strands by neutron irradiation obtained in the newly established collaborative framework are presented, and general mechanisms for the property changes are introduced.
There are high expectations for RE123 wires to be used as future commercial superconductors in the future because of their excellent performance under high magnetic fields and of low cost capabilities. ISTEC, national institutes, universities and companies are taking part in a Japanese national project on electric power devices known as, "Materials & Power Applications of Coated Conductors (M-PACC)". The target applications of the project are SMES, cables and transformers. ISTEC, Fujikura, Showa, Sumitomo and Furukawa are developing RE123 wires for mass-production using various fabrication processes. One of the most important characteristics for practical superconducting wires is, the bending-strain dependence of the critical current. The IC dependencies of RE123 wires for various bending strains were measured using the "Goldacker type" continuous bending apparatus. For tensile bending with the superconductor layer on the outside of the bend, the diameter of the 95% IC retentions was approximately 20 mm for all wires. On the other hand, for compressive bending with the superconductor layer on the inside of the bend, the IC dependencies for the bending diameter were each different. The reversibility strain under bending and straightening was also evaluated using the continuous bending apparatus. These results demonstrate that the IC dependencies for the bending diameter of all wires are suitable for the applications of the M-PACC project.
Magnetic levitation systems using HTS bulks, such as magnetic bearing devices for flywheel energy storage systems, transporters, linear actuators, magnetic gears and so on, have been developed by many research groups. Most of the HTS magnetic levitation systems are composed of HTS bulks and permanent magnets. "Stable magnetic levitation without any other control system" is a specific characteristic of the HTS bulks. A non-contact spin processor and a magnetic-levitation seismic isolation device are introduced as magnetic levitation systems that are composed of HTS bulks and permanent magnets. Furthermore, an active magnetic levitation system using spherical HTS bulks for inertial nuclear fusion and a three-dimensional HTS actuator are introduced as magnetic levitation systems with HTS bulks and electromagnets. Levitation force, levitation gap and stability are closely related to the size and shape of the HTS bulk, the magnetic field distribution around the HTS bulk, the conditions in the field-cooling process of the HTS bulk and so on. Achieving large levitation force, large levitation gap and highly stable levitation is very important for practical use of the HTS magnetic levitation system. Theoretical analysis using a numerical simulation code for understanding electromagnetic behaviors within the HTS bulk is useful for improving the levitation force, levitation gap and stability. Finally, numerical techniques based on the finite element method are introduced in this paper.
There are expectations for high-temperature superconducting (HTS) power cables as a compact cable with large capacity and low-loss power transmission. Recently, the stable manufacture of many long REBCO (RE = rare-earth element) tapes has been achieved. REBCO tapes have a high critical-current density, and the AC loss resulting from the parallel magnetic field is extremely small because of the thin-film structure of the superconducting layer. The basis of the M-PACC (Materials & Power Applications of Coated Conductors) project is to develop a process technology for fabricating REBCO tapes and promote development aiming toward the commercialization of superconducting cables using REBCO tapes. Two types of HTS cables are being developing as part of this project. These cables have superior transmission efficiency, lower loss and larger capacity than existing power cables. One is a 66 kV/5 kA three-core large-current cable and the other is a 275 kV/3 kA single-core high-voltage cable. There are several development targets. We examined factors such as AC loss, thermal characteristics of the cables under over-current and the optimum cable design. This paper provides an overview of the project and describes its progress.
Superconducting direct detectors operating at very low temperature less than 4 K have extremely high performance that cannot be obtained by semiconductor-based detectors. The superconducting direct detectors measure or count the arrival of energy quanta such as photons from sub-mm to the γ-ray region and phonons created by molecule incidence. There are three types: calorimeter, junction, and nanostrip detectors. The specifications of concern are spectral resolution, time response, and operating temperature. According to the requirement, the best type of superconducting direct detector is used for scientific and industrial applications such as, for example, dark matter search, X-ray materials analysis, mass spectrometry, and quantum communications.
Synopsis: In this study, we propose a new undulator structure based on a bulk high-temperature superconductor stacked array for insertion devices in synchrotron radiation facilities and free-electron laser devices. A strong periodic magnetic field can be generated in a short period from induced currents in the stacked bulk high-temperature superconductors. This study describes the principle of operation and features of the undulator, and shows the results of generation and control of the periodic magnetic field. We have also developed a numerical model for estimating the performance of the undulator. Excellent performance is expected at approximately 20 K.
In the JT-60SA project, the JT-60U tokamak is replaced with a full superconducting tokamak. The heliumrefrigerator cools the superconducting coils by circulating supercritical helium of 4.4 K and 0.6 MPa in the circulation loop atcertain mass flow rate. Since the cooling power of the helium refrigerator is determined by the heat load of the superconductingcoils, estimating the heat generation and required mass flow rate to acquire sufficient temperature margin is of crucial importance.In this paper, we attempted to optimize the mass flow rate in the superconducting coils to satisfy a temperature margin of 1 K. Wethen show that the consequent maximum pressure drop in the circulation loop that results in minimizing the heat load of thesupercritical helium circulation pump is 81 kPa.
Synopsis : The current status of large-grained RE-Ba-Cu-O (RE: Y or rare earth elements) bulk superconductors with excellent superconducting properties is described. Gd-Ba-Cu-O bulk superconductors can trap a very high magnetic field even if they are melt-processed in air. Although the electromagnetic force caused by the trapped field is larger for a larger sample and may break the sample, a large sample of Gd-Ba-Cu-O 46 mm in diameter has the potential of trapped magnetic fields greater than 10 T at around 40 K. In addition, single-grained bulk superconductors as large as 150 mm can be obtained using the RE compositional gradient method. Dy-Ba-Cu-O is an ideal material for current leads because it has low thermal conductivity and high critical current density at 77 K in high magnetic fields. Eu-Ba-Cu-O has low magnetic permeability, and is therefore suitable for bulk NMR applications. Progress in machining technology has made possible various bulk superconductors with complicated shapes such as coils, leading to small and strong electromagnets by stacking several coil-shaped bulk superconductors together.
The strain effect on critical current (Ic) in REBCO coated conductors has been intensively investigated owing to its importance for practical applications. The change in Ic with applied strain can be divided into two phenomena; namely reversible variation within elastic deformation for superconducting film, and irreversible degradation related to brittle fracture. REBCO coated conductor is the first material among various high temperature superconductors in which the non-linear reversible change in Ic with uniaxial strain is markedly observed. High stress (strain) tolerance in coated conductors is one of the advantages compared with other superconducting composites, and there are high expectations for application to high-field magnets based on such superior mechanical properties. In this review article, recent research results on the mechanical properties of REBCO coated conductors are summarized, including the stress-strain characteristic for substrate materials, the strain effect on Ic and the experimental techniques for evaluating these properties. Delamination has been recognized as one of the most critical issues for coil applications. Several evaluation methods for delamination strength and interlaminar fracture toughness were introduced.
In this article, the development progress of our GdBaCuO 30-kW-grade bulk HTS motor is presented. Two main features will be described here: the addition of the bulk HTS field poles using magnetic particles, and the amelioration of the condensed-neon cooling system through the addition of a gaseous helium phase. Owing to this new cooling procedure, the cooling time of the motor was reduced by more than 30% and the flux decay following the in-situ magnetization of the bulk HTS was halved. The addition of magnetic particles into the Gd-123 bulks allowed a 1.1- to 1.4-fold trapped flux density and an additional reduction of the flux decay from 7% to approximately 4% after five hours of synchronous operation under an AC field.
Cryogenic slush fluids, such as slush hydrogen and slush nitrogen, are two-phase single-component fluids containing solid particles in a liquid. Their density and refrigerant capacity are greater than those of a liquid-state fluid alone. Owing to these advantages, there are high expectations for use of slush fluids in various applications such as a clean-energy fuel, fuel for space-planes to improve the efficiency of transportation and storage, and as a refrigerant for high-temperature superconducting power machines. Experimental tests were performed with slush nitrogen to obtain the frictional pressure drop flowing in a horizontal pipe with an inner diameter of 15mm and a length of 400mm. The primary objective of the study was to investigate the pressure drop reduction phenomenon according to changes in velocity and solid fraction. The pressure drop correlation between the friction factor and the Reynolds number was obtained, and an empirical correlation between them was derived. The flow pattern for slush nitrogen inside a pipe and the behavior of solid particles were observed using a high-speed video camera and the PIV method. From the experimental results, the pressure drop reduction phenomenon emerged clearly when the flow velocity was higher than 3.6m/s and the flow pattern of solid particles inside the pipe was pseudo-homogeneous.
The applications of REBaCuO superconducting bulks (RE: rare earth element or Y) have been investigated recently because of the enhancement of the superconducting characteristics such as critical current density Jc and the trapped field BT. A superconducting bulk can trap higher BT of over 17 T via conventional field-cooled magnetization (FCM) and BT=5.2 T via pulsed field magnetization (PFM), which has been intensively studied because a superconducting magnet is not used. This review article summarizes the magnetizing mechanism of the superconductors, the recent activities of PFM conducted experimentally and numerically, and the practical applications of several superconducting bulk magnet devices.
Mechanical properties of melt-growth GdBa2Cu3Ox, (Gd123) superconducting samples with 10 wt.% Ag2O and 0.5 wt.% Pt were evaluated at 77 K through flexural tests for specimens cut from the samples in order to estimate the mechanical properties of the Gd123 material without metal substrates, buffer layers or stabilization layers. We discuss the mechanical properties; the Young's modulus and flexural strength with stress-strain behavior at 77 K. The results show that the flexural strength and fracture strain of Gd123 at 77 K are approximately 100 MPa and 0.1%, respectively, and that the origin of the fracture is defects such as pores, impurities and non-superconducting compounds. We also show that the Young's modulus of Gd123 is estimated to be 160-165 GPa. (C) 2013 Elsevier Ltd. All rights reserved.
A number of experimental and theoretical studies have been performed to understand the mechanism of high-Tcsuperconductivity and to enhance Tc. High-pressure techniques have played a very important role for these studies. In this paper,the high-pressure techniques and physical properties of high-Tc superconductor under high pressure are presented.
This study investigates superconducting and mechanical properties of monolayer GdBa2Cu3Oy-coated conductor coils under large electromagnetic stress. We found that reversible superconducting properties can be achieved in the large hoop stress/strain states up to 1288 MPa/0.63% for the Hastelloy-outside-winding coil (coil A). This limit is larger than the results for the tensile test of the short sample. However, damage occurred near the current terminal at 640 MPa for the Hastelloy-inside-winding coil (coil B). It is considered that the degradation was due to the stress concentration at the edge of the current terminal. In the case of the Hasetelloy-inside-winding coil with a lap joint (coil C), the coil performance is limited by the shear stress of the lap joint.
Fe-sheathed MgB2 superconducting tapes were prepared through an ex-situ process and powder-in-tube (PIT) technique using powders treated in organic acid solutions. The treatment realizes the substitution of carbon, derived from the remnants of the organic solvents being adsorbed onto the surface of MgB2 grains, into boron in MgB2 and pulverization of MgB2grains. The amount of carbon substitution is x = 0.02−0.03 in MgB2-xCx. The carbon substitution is effective for increasing Bc2,and grain boundaries act as pinning centers. Therefore, this improves the Jc property of tapes in the high-magnetic-field region.Depending on the solution, the Jc values at 4.2 K and 10 T increase up to ten times compared to tapes using powders withouttreatment. These values are comparable to those obtained for the ex-situ processed tapes with the best-ever reported performance.Tapes using MgB2-xCx (x ≥ 0.05) powders clearly show weak grain coupling, and hence the enhancement of transport Jc is limited.
A new Japanese national project has started in 2008 to develop high temperature superconducting electric power devices. In this project, we have developed a superconducting magnetic energy storage (SMES) system, which are highly expected as a stable power supply. Main issues are a large current capacity conductor made of YBCO-coated tapes and a compact coil wound the conductors. Aiming at the manufacturing of compact coil with higher energy density through the creation of higher magnetic field, we produced YBCO coil, and by carrying out hoop stress tests. Also, aiming at the development of 20 MJ class SMES component coils necessary for picturing the technological outlook of 2 GJ class SMES coil for power system control, we manufactured component coils (outer diameter 650 mm), adopting the bundled conductor that would enable the realization of high strength and low loss, proving that its current capacity was large enough to exceed 2.6 kA, through basic verification test for energization. In addition, we have challenged the development of high efficiency coil conduction cooling technology, stable manufacturing technology of coated conductors for SMES and the highly reliable/highly durable SMES coil component technology.
