Y-based Oxide Research Articles

Numerical Evaluation of Reinforcement Structure Against Electromagnetic and Thermal Stresses in Stacked REBCO Pancake Coils

In recent years, high field REBCO coils have been applied with great interest to NMR and accelerators due to their high thermal stability and high current density. However, deteriorations and damages of REBCO coils are occurring. During the charge and discharge of REBCO coils, screening currents are induced to circulate in the windings, resulting in a non-uniform current distribution in the wires. It has been reported that the electromagnetic force distribution in the wire becomes significantly non-uniform, resulting in degradation of REBCO coils. In this study, the effects of stress and deformation of REBCO coils were investigated through electromagnetic stress analysis using two-dimensional axisymmetric structural analyses, taking into account thermal stress during cooling, tension during winding and electromagnetic force during not only charge and but also discharge, and the suppression of stress and deformation by the currently devised YOROI—coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure and over-banding was evaluated.

Numerical Evaluation on Mechanical Behavior of No-Insulation REBCO Pancake Coils in Small-Scale Model of Skeleton Cyclotron

We are developing a high-temperature superconducting (HTS) air-core compact cyclotron, named Skeleton Cyclotron (Ueda <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> 2013), (Ueda <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> 2019), that can accelerate various particles and variable energy for radioisotope (RI) production. The coil system of Skeleton Cyclotron consists of circular main coils and noncircular sector coils which are wound by REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+δ</sub> (REBCO) tape applied no-insulation (NI) winding technique for both high current densities and thermal stabilities. The electromagnetic and thermal behaviors in NI coil differs from those in conventional insulated coils during charging, discharging, and quenching. Therefore, it is necessary to investigate the mechanical behavior and reinforcement structure of multiple NI coils in Skeleton Cyclotron. In this study, we report on the numerical evaluation of mechanical properties of NI REBCO coils in Skeleton Cyclotron at charging and quenching considering the current distributions and electromagnetic stresses unique to NI coils. In the quenching process, the radial current in a quenching pancake of the sector coil became dominant, resulting in generating the rotating force and non-symmetric deformation. YOROI-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure is effective for the additional magnetic stress.

Mechanical Strength Evaluation of a Yoroi-Coil Structured Non-Circular REBCO Pancake Coil in High Magnetic Field

In order to achieve a high intensity and compact multifunctional air-core cyclotron, the behavior of non-circular coils in a high magnetic field at 4.2 K were investigated. Two types of isosceles triangle shaped double-pancake coils: a coil with reinforcement by Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structuring and a coil without reinforcement, were manufactured and their behaviors were observed when current was applied to each coil in a high magnetic field. The non-reinforcement coil showed in 10 T external magnetic field that the superconducting properties of the coil were partially lost and a voltage generated in the coil winding was observed when the applied current exceeded 160 A. After disassembling this coil, it was found that the superconducting tape in the coil winding was plastically deformed and permanently bent at the corners. The reinforced coil due to Yoroi-coil structuring was powered up to the coil current of 300 A in a magnetic field of 14 T. A voltage of 0.3 mV was observed when the coil current was 277 A, and the excitation was terminated when the voltage reached 0.6 mV at 300 A. The coil winding, after the current flowing up to 300 A in 14 T field, indicated that the deformation of it was significantly limited. It was confirmed that the Yoroi-coil type structural reinforcement, even for triangular coils, has sufficient mechanical strength under the conditions of our air-core cyclotron.

Numerical Evaluation of Thermal and Electromagnetic Stress in Frame-Reinforced Stacked REBCO Pancakes Coils

To achieve high-field rare-earth barium copper oxide (REBCO) coils, the mechanism of the deterioration of or damage to such coils needs to be clarified. A REBCO coil experiences various stresses and strains during the winding, cooling down, charging, and discharging processes. Furthermore, the additional force and stress due to a screening current has become an issue in REBCO coils. To protect REBCO coils from large electromagnetic stress in a high field, a reinforcement structure called the Y-based oxide superconductor and reinforcing outer integrated (YOROI) coil was proposed. This study numerically evaluated the effect of the YOROI coil structures against thermal and electromagnetic stress using a two-dimensional axisymmetric structural analysis. This simulation considered the following: 1) the mechanical stress induced by 10 N of winding tension, 2) thermal stress during cooling from 300 K to 10 K, and 3) electromagnetic stress, which included the additional stress due to a screening current during the charging process. The mechanical behavior due to each process was investigated, and the effect of the YOROI structures was also examined.

Microstructure Evolution in ODS Alloys with a High-Volume Fraction of Nano Oxides

Existing oxide dispersion strengthened (ODS) alloys are, besides Ni-based superalloy single crystals, the most creep-resistant materials. The creep resistance of the ODS alloys may, moreover, be significantly improved thanks to increasing the volume fraction of the nano oxides by more than one order of magnitude so that the oxides play a decisive role in strengthening. The present experimental study deals with two systems of such a high-volume fraction of nano oxides, namely, the Fe-11Al-1O and Fe-17Cr-7Al-4Y2O3 systems prepared by mechanical alloying and hot rolling leading to a rather stable fine-grained microstructure. This microstructure undergoes static recrystallization at high temperatures. The kinetics of static recrystallization and coarsening of nano oxides in recrystallized grains is determined for both systems. The difference in kinetics of coarsening of Al-based and Y-based oxides in the Fe-11Al-1O and Fe-17Cr-7Al-4Y2O3 systems is expressive and predetermines the Fe-17Cr-7Al-4Y2O3 system or similar ones to become the new leading system among creep- and oxidation-resistant materials for applications up to 1200 °C.

Numerical Evaluation of the Reinforcing Effect of the Advanced YOROI Coil Structure for the HTS Coil

REBCO coils applied to superconducting magnetic energy storage system, magnetic resonance imaging, medical accelerator, and so on, are expected to result in high efficiency and compactness due to the realization of higher magnetic field and current density. Because these devices require large coil radius, huge hoop stress “BJR” (= magnetic field × current density × coil radius) is produced in the coil winding and the damage to these devices is likely to cause. In our previous study, we proposed a novel coil structure called the Y-based oxide superconductor and reinforcing outer integrated (YOROI) structure to achieve a high-strength REBCO pancake coil. The YOROI structure comprises upper and lower plates and the outer frame of the winding outer periphery. The frames are forcibly expanded by the superconducting coil winding situated inside when the coil winding is subjected to an electromagnetic force. The outer frame is connected to the upper and lower plates and transfers a part of the electromagnetic force from the coil winding to the reinforcing outer plates. The reinforcing outer plates then support the coil to suppress the coil deformation against the electromagnetic forces. The YOROI structure achieved the resistance to a maximum hoop stress of 2 GPa, which was calculated from the BJR in an excitation test at 4.2 K in 8-T backup fields. In this study, we investigated the effect of the stress control structure to realize the HTS coil with a mechanical strength of over 2 GPa using a three-dimensional finite-element structural analysis.

Progress of "Yoroi-coil Structure" in Mechanical Strength with High Current Density

Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure has been developed to fabricate very strong pancake coils against electromagnetic force. In Yoroi-coil structure, the outer supporting structure is effective to make a mechanically robust coil having a high current density in the case that the hoop stress must exceed the yield strength of a REBCO-coated conductor without this reinforcement. By the experiments and analysis, we pointed out that the remarkably weak delamination stress can cause the delamination of the coated conductor in coils. So that Yoroi-coil structure has advantages to delamination because it could maintain a coil shape with reinforcing materials, without impregnation. Since higher current density is required by various applications, the Yoroi-coil using austenitic stainless steel reinforcing frames and plates, has been verified by the hoop stress test with high current density. Then, high coil current density of 446 A/mm 2 was achieved by the Yoroi-coil-structured double pancake (DP) coil, with the total number of the winding turns of 574, at 4.2 K in the back-up magnetic field of 11 T. The inner and outer diameters of the DP coil were 190 and 250.1 mm, respectively. Although the hoop stress evaluated on the assumption of excluding the supporting structure exceeds 1 GPa, Yoroi-coil structure restricted the strain of coil winding ranging 0.2% to 0.3%. The stainless steel reinforcing member well supported a part of electromagnetic force in Yoroi-coil structure, even with high coil current density.

Experiment and Numerical Analysis on the YOROI Structure for High-Strength REBCO Coil

To achieve a high current density and a compact REBCO coil, a reinforcing structure is essential to prevent coil degradation and deformation caused by the large Lorentz force. A new reinforcing structure for the REBCO coil called the Y-based oxide superconductor and reinforcing outer integrated (YOROI) coil was proposed in the previous study. The YOROI coil, which exhibited no degradation after an excitation test with a maximum hoop stress of 1.7 GPa at 4.2 K in 8-T backup fields, has great ability to reduce the stress and strain acting on the coil winding to maintain the coil shape and prevent degradation in the REBCO wire. In this study, the hoop stress in the winding and the stress shared by the reinforcing structure of a YOROI model coil were measured at 40 K in 10-T backup fields to clarify the reinforcing mechanism of the YOROI coil. A three-dimensional structural analysis, which simulated the experimental condition, was performed on the model coil to determine the distribution of stress and strain in the winding and reinforcing structure.

Strengthening Effect of “Yoroi-Coil Structure” Against Electromagnetic Force

The strengthening of Yoroi-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure at stronger electromagnetic force was investigated using the Yoroicoil structured double-pancake coil with higher strength outer plates of carbon-fiber reinforced plastic (C-FRP) than those of glass-FRP. The coil achieved 1.14 kA transporting at 4.2 K in 14-T back-up magnetic field and the superconducting wire was burnt by thermal runaway after that. The calculated maximum hoop stress, based on the BJR (magnetic field × current density × coil radius) calculations, at the hoop stress test reached 2.0 GPa. This value was far exceeding the tensile strength of superconducting wire ranging from 1 to 1.3 GPa; however, the maximum strain of superconducting wire in the test coil was held about 0.5%. Yoroi-coil structure is useful for the applications, which need high magnetic field precision. The strengthening effect of C-FRP outer plates was observed at outer part of the coil, but it did not cover the whole coil body, so that arrangement of reinforcing outer plates could admit of some improvement.

Development of Non-Circular REBCO Pancake Coil for High-Temperature Superconducting Cyclotron

A series of feasibility studies are carried out on the applications of a high-temperature superconducting (HTS) magnet system to a heavy-ion accelerator for particle cancer therapy. A novel HTS cyclotron is expected to be more compact and have higher efficiency than a conventional heavy ion synchrotron accelerator. A high current density is required for the HTS magnet to realize a compact HTS cyclotron. Further, a high-strength reinforcing structure is absolutely essential for the HTS magnet owing to the large Lorentz force caused by the high current density to prevent the magnet deformation and maintain the required high accuracy field. In a previous study, a novel coil structure called the Y-based oxide superconductor and reinforcing outer integrated “YOROI coil” was proposed and tested at 4.2 K in 8-T backup fields. The YOROI model coil exhibited no degradation after the excitation test with a maximum hoop stress of 1.7 GPa determined by the product of the magnetic field, current density, and coil radius. The mechanism of stress sharing between the coil winding and the reinforcing structures of the YOROI coil was numerically determined. In addition, the electromagnetic and mechanical properties of a reinforcing structure based on the YOROI coil for circular REBCO coils assuming part of the HTS cyclotron magnet system was also numerically simulated in the previous paper. In this study, a new reinforcing structure is proposed on the basis of the YOROI coil for a non-circular REBCO coil assuming part of the HTS cyclotron magnet system. The electromagnetic and mechanical properties for the new reinforcing structure are numerically determined. As a result, the proposed reinforcing structure has great ability to reduce the stress and strain acting on the coil winding to maintain the coil shape and prevent degradation in the REBCO wire.

Development of High Strength Pancake Coil With Stress Controlling Structure by REBCO Coated Conductor

High strength against electromagnetic force is required for high magnetic field and large capacity coil in order to develop large-capacity superconducting magnetic energy storage (SMES) systems for electric power system control. Also, suppression of delaminating of Yttrium (Y) based coated conductor in a coil is required to manufacture the highly reliable and durable superconducting coil. Insulating coating, using liquid resin of low-temperature-curable-polyamide, was developed and showed durability at very low temperature without deterioration of transport properties of superconducting wire in a coil. Combining paraffin molding, delaminating, and deterioration of transport properties of superconducting wire were not also observed in a coil. These insulating techniques were applied to the pancake coil, in which superconducting wire and the reinforcing outer plates of the coil withstand electromagnetic force. The double pancake coil of this coil structure, called “Yoroi-coil; Y-based oxide superconductor and reinforcing outer integrated coil” was prepared and the durability against electromagnetic force by hoop stress test was verified. The coil achieved 1.5 kA transporting at 4.2 K in 8 T back-up magnetic field without the degradation of transport properties. Maximum hoop stress at the hoop stress test reached 1.7 GPa, based on the calculations. This result confirmed that Yoroi-coil structure has a capability to withstand the large hoop stress, which exceeded the tensile strength of Y-based coated conductors, and bring out highly durable and reliable superconducting coils.

高強度パンケーキコイル構造（Yoroi-coil）の開発

A high-strength pancake-coil structure called “Yoroi-coil" (Y-based oxide superconductor and reinforcing outer integrated coil), in which superconducting wire and the reinforcing outer plates of the coil withstand electromagnetic force, was developed for high magnetic field applications. The double-pancake (DP) coil of this coil structure was prepared and verified for durability against electromagnetic forces using the hoop stress test. The coil achieved 1.5 kA transporting at 4.2 K in an 8 T backup magnetic field without degradation of transport properties. Maximum hoop stress at the hoop stress test reached 1.74 GPa, based on the calculations. This result confirmed that the “Yoroi-coil" structure has the capability to withstand large hoop stress, which exceeds the tensile strength of Y-based coated conductors, not only owing to the strength of superconducting wire but also owing to the integration of the whole coil structure itself. Additionally, the strengthening effect of the structure was verified by analysis.

Development and Prospects for the Future of Superconducting Wires

Superconducting wires are important from the viewpoints of energy saving and the realization of a low-carbon society, because their applications in various types of electric power applications enable not only improved efficiency but also the reduction of size and weight owing to the fact that they can allow a large electric current density without resistance. Wires of Nb–Ti and Nb3Sn metallic superconductors have conventionally been used in various magnets. The research and development of high-temperature Cu-oxide superconducting wires has been intensively carried out focusing on Bi- and Y-based oxides; recently, the development of long wires of these oxides has also been in progress, and their applications to a variety of power systems are being eagerly discussed. MgB2, whose superconductivity was discovered in Japan in 2001, is also being studied with the aim of fabricating MgB2 wires, and promising performance has been obtained. The research and development of superconducting wires using these materials is expected to achieve further progress and lead to their practical applications in the future.

Atomic beam deposition of lanthanum- and yttrium-based oxide thin films for gate dielectrics

We report on the electrical and microstructural characteristics of La- and Y-based oxides grown on silicon substrates by ultrahigh vacuum atomic beam deposition, in order to examine their potential as alternate gate dielectrics for Si complementary metal oxide semiconductor technology. We have examined the issues of polycrystallinity and interfacial silicon oxide formation in these films and their effect on the leakage currents and the ability to deposit films with low electrical thickness. We observe that polycrystallinity in the films does not result in unacceptably high leakage currents. We show significant Si penetration in both types of films. We find that the interfacial SiO2 is much thicker at ∼1.5 nm for the Y-based oxide compared to the La-based oxide where the thickness is &amp;lt;0.5 nm. We also show that while the Y-based oxide films show excellent electrical properties, the La based films exhibit a large flat band voltage shift indicative of positive charge in the films.

Development of Reinforced Magnet Rings for High Speed Rotation. Magnet Rings for Super Conducting Magnetic Bearing in the Flywheel Type Energy Storage System.

The investigation of flywheel type energy storage system has been brisk in these days after discovered Y-based oxide superconductors according to the high potential fewer rotational loss for magnetic bearing even in the temperature (77K) of liquid nitrogen. Permanent magnet rings are applied to the rotational part, and high speed rotation is required to the magnet. The magnet itself is fragile material in the tensile stress, but it is strong enough in the compressive stress. Then authors designed the pre-compressed magnet rings by the multiple layer CFRP hoops. Three of the manufactured pre-compressed magnet rings rotated at the rotation speed of 33723rpm, 33472rpm and 33506rpm respectively at the rotation tests and the values of them were almost the same as the calculated value of 31300rpm.

SRPM法によるY系酸化物超伝導体の周波数依存性

SRPM法によるY系酸化物超伝導体の周波数依存性

On the physical nature of the wide band at 2.8 eV in the visible luminescence spectrum of high- Tc superconductors

Photoluminescence spectra of different Bi- and Y-based oxide high- T c superconductors are measured under laser excitation ( E exc = 4.03 eV). A wide luminescence band with a maximum near 2.8 eV is investigated and its temperature evolution (20-300K) is followed. Comparison of the spectra of various materials and their temperature evolution permits us to draw conclusions about local luminescence centers in the bulk. The experimental data are used to propose a model of a charge-transfer excimer complex involving the F-center and the negative molecular oxygen ion. In spite of the low quantum yield, the luminescence of such centers can be observed due to absence of the radiation electron-hole recombination. Analysis of experimental data suggests the existence of a strong radiationless relaxation over discrete levels inside the optical pseudo-gap which competes with the radiation recombination.

8MWh級高温超電導浮上式フライホイール電力貯蔵システムの概念設計および適用性の検討

When combined with a magnet having a magnetic field gradient (for example, a permanent magnet), a Y-based oxide superconductor is capable of forming a non-contact bearing with a strong levitational force. Since this bearing exhibits low rotational loss, it is very likely to form a highly efficient power storage system in combination with a flywheel. In this study, an 8 MWh power storage system utilizing a flywheel was conceptually designed to examine its applicability and the possible effects of its introduction. In this study, it was found that this system was an effective power storage.

The cooperative effect of electronic structures in high Tc superconductor YBa 2Cu 3O 7−δ system

Different temperature quenched YBa 2 Cu 3 O 7−δ samples have been investigated by means of X-ray photoelectron spectroscopy(XPS). The binding energy shift and the shape variation of Y3d and Ba3d 5/2 show some correlation with superconductivity of the samples. It is suggested that the superconductivity of Y-based oxides may come from the cooperative effect of the components other than from the CuO 2 layers or Cu-O chains only.

Observation of possible superconductivity at 230 K

Recently, Chu1 announced the observation of sharp drops of up to two orders of magnitude in the resistance of several Y-, Sc- and La-based multi-phase Ba–Cu oxide samples at temperatures as high as 240 K. The resistance drops reported did not survive the thermal cyclings for magnetic measurements. Later, M. H. Cohen (personal communication) reported similar anomalies in some Y-based oxides. In the absence of zero resistivity and evidence for the Meissner effect, the sharp resistance drops have been taken only as an indication of the possible existence of superconductivity at these unusually high temperatures. More recently, Chen et al.2 detected the reverse a.c. Josephson effect in mixed-phase Y–Ba–Cu oxide samples below 240 K, providing the strongest evidence for superconductivity to date. Here we report the observation of a sharp decrease in resistance of at least four orders of magnitude at ∼230 K in one annealed sample of EuBa2Cu3O6+δ. Subsequent magnetic measurements on the same sample indicated a magnetic anomaly at the same temperature.