Search

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. [ABSTRACT FROM AUTHOR]

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/mm2 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. [ABSTRACT FROM PUBLISHER]

Abstract: Development of apparatuses for protecting industrial facilities such as semiconductor plants or information industries from instantaneous voltage dips, which requires very large output power, has been expected. A Superconducting magnetic energy storage system (SMES), one of such apparatus, consists of superconducting magnets that must withstand high voltage during operation and require high reliability. We have already development of SMES using conventional superconducting coils and done the field test of the SMES for bridging instantaneous voltage dips. After field test, the commercial SMES for instantaneous voltage dips is working there. Since field test has started, we have confirmed nearly 40 operations, and all have succeeded. In 2011, three commercial SMES units for bridging instantaneous voltage dips are operating in Japan. [Copyright &y& Elsevier]

Reports on a study of a high temperature superconducting magnet made with Bi-2212/Ag Rutherford cable. Inside and outside diameters of the magnet; Coil operation; Maximum magnetic field in liquid helium; Excitation tests under the high-speed rate of change of magnetic field; Estimation of the value of alternating current losses using the change of liquid helium level.

Reports on a study on high temperature superconducting magnetic bearing for ten kilowatt-hour flywheel energy storage system. Development of the advanced cooling system of the bearing with a cryogenic refrigerator; Study of bearing characteristics in several cooling conditions; Repulsive force of the bearing; Rotating loss of the bearing; Relation between rotating speed and loss.

Discusses the design and fabrication of a termination for 77kV-class high Tc superconducting power cables. Design of termination; Experiments on the termination system; Discussion and conclusions.

Abstract: New Horner–Wadsworth–Emmons reagents, (o-t-BuPhO)2P(O)CH2CONMe(OMe) and (o-t-BuPhO)2P(O)CH2CON(CH2CH2) 2O were prepared via the Arbuzov reaction in good yields. The HWE reaction of these reagents with a variety of aldehydes gave cis-α,β-unsaturated amides with high selectivity in almost quantitative yields. [Copyright &y& Elsevier]

A Superconducting Magnetic Energy Storage (SMES) system has good characteristics as energy storage equipment in electric power systems such as high efficiency, quick response and no deterioration in repetition operation. Since 1991, the Agency for National Resources and Energy Japan has carried out a national project to develop an SMES for power control in power systems. Moreover, SMES has been developed to bridge for instantaneous voltage dips since 2003. A field test of 5 MVA SMES for bridging instantaneous voltage dips was carried out on an advanced large liquid crystal TV plant in Kameyama from July 2003. Before that, a 10 MVA SMES system was working there. After the field test, the commercial SMES for instantaneous voltage dips is working there. In 2015, three commercial SMES units for bridging instantaneous voltage dips are operating in Japan. These SMESs are all equipped with metal superconducting coils. When considering cost-reduction, size-reduction, and maintenance of the SMES in the future, it is necessary to develop a SMES with a high-temperature superconductor and improve the efficiency of its cooling system. We have also developed and conducted operation tests of SMES with a Bi2212 oxide superconductor and high performance cryocooler which enable energy conservation operation by inverter control. In this paper, developed results on cooling systems and cryocooler for SMES are presented. [ABSTRACT FROM AUTHOR]

This paper reported the fabrication and the test results of the high temperature superconducting (HTS) magnet developed for the aluminum billet heater for aluminum extrusion processing. In this magnet, the HTS coils were combined with iron cores, because the required magnetic field in the working region was about 1T. Two HTS coils wound directly on the convex shape iron cores were fabricated. The HTS coils were made by the no-insulation winding of REBCO tape with the YOROI-coil technique. Each of them was separately installed in an individual cryostat. Two HTS coils with iron cores were disposed oppositely to each other and were magnetically connected by a C-shape yoke placed in room temperature. The HTS coil was cooled down to about 15 K by the GM cryocooler in the initial cooling. The magnetic field of 1.06 T at the center of the heating region was stably generated with the rated current of 200 A. It was also demonstrated that the HTS magnet could be charged up to 300 A without quench. According to the observation of the electromagnetic force direction from the outside of the cryostat, it was confirmed the validity of the force balance design of the magnet. [ABSTRACT FROM AUTHOR]

YBCO superconducting wire has a relatively low decrease in power distribution at high temperatures and under a high magnetic field. A high-intensity substrate is used for the wire, so the wire has high machine characteristics. Therefore, it is expected that this wire can be used for large-scale high magnetic field coils. Here, coordination between the SMES system for 100 MVA/2 GJ class load fluctuation compensating was conducted using IBAD/CVDYBCO wire. The SMES system includes a toroidal type YBCO coil consisting of 180 compact, high magnetic field multi-unit coils, a large coil cooling system that uses the conduction cooling method, which does not use a refrigerant medium, and a multi-cell power converter that achieves multi-unit coil connection with relatively low current and low voltage. Studies were conducted for each individual device and for the whole system. Based on the study plan in this paper, it has become possible to develop and coordinate each device of the 100 MVA/2 GJ class power system load fluctuation compensation SMES system using YBCO wire, which up until now had seem impossible as an actual system. [ABSTRACT FROM AUTHOR]

Magnetic field dependencies of the Ic of the IBAD/CVD-YBCO short tape sample and its small coil sample were measured in high fields, up to 18 T at 77 K. Compared with the Ic of the tape sample, the Ic of the coil sample at 0.1 μV/cm showed the same tendency in high fields. If YBCO tape is applied to a high-field coil application, the application should be operated at a temperature which is lower than 77 K. Using long CVD-YBCO tape, six stacked pancake coils were fabricated. Various current tests were conducted using one of these stacked coils. In AC current tests, thermal stability of the YBCO coil was estimated. When the peak values of AC current were 1.2 times higher than the maximum DC current in a thermal stable state, Idcmax, and the average electric field of the coil at the first triangular wave was about 10 times higher than 1 μV/cm criterion, the peak values of the built-up voltage did not tend to increase even after the 99th triangular wave current, and thermal run-away in the coil was not observed. In DC current with overlapped pulse current tests, the maximum peak current of the coil in a thermal stable state was obtained as a function of DC current and sweep time. It was 1.3 times higher than Ic and 1.4 times higher than Idcmax in a test condition. These results indicate that the YBCO coil has high potential in short-time, over-current operations at high temperatures. In cases where built-up voltages did not disappear, they began to increase just after the coil currents reverted to the initial DC currents. It was found that DC current influenced the increasing speed of built-up voltages once the pulse current had decreased to zero. [ABSTRACT FROM AUTHOR]

Mechanical properties of YBaCuO superconducting tape produced by a multi-stage metal-organic chemical vapor deposition (MOCVD) technique have been investigated. It is important for YBaCuO superconducting tape to tolerate stress strain and maintain flexibility in order to be used for electric power applications, magnetic applications, and so on. At this time, we have produced an approximately 0.25 μm YBaCuO layer on a pulse laser deposition (PLD)-CeO2/ion beam assisted (IBAD)-Gd2 Zr2 O7/Ni-based alloy substrate by an MOCVD technique, and approximately 4 μm Ag was sputtered on it as a protective layer. The thickness of each layer was approximately 1.0 μm, 1.0 μm and 0.1 mm respectively. Its critical current was about 50 A. The mechanical properties of YBaCuO tape formed on Ni-based alloy substrates with a CeO2 /Gd2 Zr2 O7, buffer layer will be described. Tensile or compressive bend stress tests were conducted, and normalized critical current and the value n were evaluated. The degradation of its critical current was confirmed not to be in the big problem level in manufacturing applications. In addition, the surfaces of YBaCuO layers were observed by scanning electron microscopy and no crack was observed on them. Next, axial tensile stress tests were conducted and the YBaCuO tape was compared with biaxially textured Ni-3at.%W alloy substrates and YBaCuO layers on Ag substrates. Axial tensile stress characteristics of the YBaCuO tape were confirmed to be much higher than others. The YBaCuO tape was confirmed to have adequate axial tensile stress characteristics for designing a coil which can tolerate electromagnetic force. [ABSTRACT FROM AUTHOR]

Super-ACE project started to research and develop the superconducting AC power equipments as a national project in 2000 fiscal year. This project is R&D of the basic technologies of high temperature superconducting (HTS) cable, HTS fault current limiter (FCL), HTS magnet for reactor and transformer. Main subjects of the cable are to develop a HTS conductor rated 3 kA, cooling technology of a 500 m HTS cable of 700 A rated current, and the analysis of integrated HTS power system. The paper describes the background of this project, its target, major results of studies, and testing schedule of 500 m cable. [ABSTRACT FROM AUTHOR]

We have been developing a new-generation accelerator named “Skeleton Cyclotron”, which is an ultra-compact and high-intensity accelerator for the stable production of 211At used for targeted alpha-particle therapy. Coil system for Skeleton Cyclotron consists of circular and noncircular high-temperature superconducting magnets and it can cause the output energy to vary without being bounded by the non-linearity of the iron core. This will enable not only the production of 211At, but also the production of radioisotopes for positron emission tomography and neutron irradiation for boron neutron capture therapy with a single accelerator. A high-precision magnetic field distribution and a high temporal stability are required for stable beam acceleration, but the screening current, which is induced in the REBa2Cu3Ox (REBCO, RE: Rare Earth) coated conductor, generates an irregular magnetic field and deteriorates the quality of the magnetic field spatially and temporally. In this study, we numerically evaluated the temporal stability and reproducibility of the screening current-induced field considering the variable energy operation for the Ultra-Baby Skeleton Cyclotron, which is a small demonstration model of Skeleton Cyclotron. [ABSTRACT FROM AUTHOR]

Abstract: A new HWE reagent, (o-tBuC6H4O)2P(O)CH2CN (2e), reacts with various types of aldehydes to give Z-α,β-unsaturated nitriles with 86% to >99% Z-selectivity. Especially, the reaction of 2e with bulkier aldehydes, both aromatic and aliphatic, gave the Z-olefins with extremely high selectivity. The combination of t-BuOK and 18-crown-6 (1equiv) is the base of choice for aromatic aldehydes and t-BuOK is generally the base of choice for aliphatic aldehydes. [Copyright &y& Elsevier]

We achieved a biaxially oriented YBa2Cu3O7 film on a {100} <001> textured Cu tape with Jc of 1.9×106 A cm-2 at 77 K. A Ni overlayer was deposited by electroplating technique on the {100} <001> textured Cu tape to improve oxidation resistance of Cu substrate, and then YBa2Cu3O7 was deposited on the CeO2/YSZ/CeO2 buffered Ni-electroplated Cu tape. We confirmed that the Ni-electroplated Cu tape lost its ferromagnetism after 700 °C at 1 h heat treatment. Our rolling assisted biaxially textured substrate (RABiTS) type coated conductor can be used for ac applications and is thought to be more cost feasible than the standard RABiTS architecture using Ni-alloy tapes. [ABSTRACT FROM AUTHOR]

In magnetic resonance imaging and nuclear magnetic resonance applications, it is important that the high-temperature superconducting coils provide a high magnetic field in a miniaturized form factor. Our research group considers these requirements to be compatible with no-insulation (NI) coils in which the thickness of the Cu stabilization layer and the turn-to-turn contact electrical resistance are key parameters that enable both high current densities and high thermal stabilities. When the Cu stabilization layer is thin, the current density is impaired, but the thermal stability is improved. If the turn-to-turn contact electrical resistance is very large, then the characteristics of the NI REBCO coil approach the characteristics of conventional insulated coils, and the thermal stability may be degraded. However, when the turn-to-turn contact electrical resistance is large, the excitation delay time is reduced. In this study, we used a combination of the partial element equivalent circuit method and the finite element method to perform a current distribution and thermal analysis of the behavior of NI REBCO coils when a local normal-state transition occurs. We also considered the appropriate turn-to-turn contact electrical resistance that could shorten the excitation delay time as much as possible while still suppressing the formation of hotspots, which is a disadvantage of the NI REBCO coil. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

A series of feasibility studies were carried out on the applications of a high-temperature superconducting (HTS) coil system for a medical accelerator system for particle cancer therapy by our group. A new HTS cyclotron is designed to be more compact and have higher efficiency than the conventional medical accelerator. High strength against electromagnetic forces is required for the development of compact HTS coils during the use of an HTS cyclotron. A new stress control structure for a high-strength REBCO pancake coil was proposed in the previous study. No deterioration was observed in the double pancake coil after a charging test of 1.5 kA at 4.2 K in 8-T backup fields. The maximum hoop stress was determined to be greater than 1.7 GPa because of the Lorentz force. The developed coil structure was able to share the hoop stress with not only the coil winding but also the reinforcing structures. In this study, numerical structural analysis based on the finite element method was performed on the new coil structure to clarify the mechanism of the stress sharing between the coil winding and reinforcing structures. In addition, the stress sharing effect of the meter-class REBCO coil assuming an HTS cyclotron system was determined. [ABSTRACT FROM PUBLISHER]

In the real application of high-temperature superconducting (HTS) coils to a superconducting magnetic energy storage (SMES) system, coated conductors are cyclically subjected to tensile strain due to electrical charging and discharging. A quench is not only caused by failure in the power supply and cooling system but also could be induced by local deterioration of the superconducting characteristics because of the cyclic strain during operation. In such a local deterioration case, the conventional detection method using voltage signal for low-temperature superconducting (LTS) coils is not applicable for the HTS coils because of the significantly slow velocity of normal-zone propagation. Furthermore, the voltage detection method is considered to be extremely difficult because the noise of the converters and other equipment is much larger than the local normal-zone voltage of the HTS coils. Therefore, a new quench-detection method for HTS coils is required. In our previous studies, a current detection method was developed for a cryocooler-cooled SMES coil wound with a kA-class laminated bundle conductor composed of four electrically insulated coated conductors. In the present study, experiments and numerical simulations were carried out on a double pancake model coil that assumes real SMES operation to verify the validity of the current detection method. [ABSTRACT FROM PUBLISHER]

The novel reagent (I) renders possible the conversion of aldehydes into the desired α,β-unsaturated nitriles. [ABSTRACT FROM AUTHOR]

In this paper, we focus on the quench detection and protection of a cryocooler-cooled pancake coil for SMES wound with a YBCO bundle conductor composed of laminated electrically insulated YBCO-coated conductors. Because the normal-zone propagation velocity is much slower in a high-temperature superconducting (HTS) coil than in a low-temperature superconducting (LTS) coil, the detection of the non-recovering normal zone using a voltage signal is quite difficult. Quench detection is considered to be more difficult during SMES operation because of the noise of the converter or other equipment. Therefore, a quench must be detected using some other method. In the previous paper, we showed that a quench in the coil could be detected by observing the transposition of the current in the bundle conductor caused by local normal transition. In this paper, based on this quench detection method, we investigate the transposition of current and the thermal behavior during the quench detection and the dumping of the stored energy by an external resistance in coils wound with a YBCO laminated bundle conductor for SMES and determine the appropriate stabilizer thickness of the YBCO-coated conductors. [ABSTRACT FROM PUBLISHER]

A reversible effect of strain on the critIcal current (Ic) has been reported for REBa2Cu3O7-δ (REBCO) coated conductors. In this study, the strain sensitivity of Ic was compared for GdBCO coated conductors with different crystal orientations. Extremely small strain sensitivity was confirmed from tensile and bending tests at 77 K for a GdBCO film with the [110] direction parallel to the tape length (Gd-F), while a GdBCO film with the [100] or [010] direction parallel to the tape length (Gd-I) has much stronger strain dependence of Ic. To compare the strain sensitivity of Ic based on internal strain, the lattIce strain was evaluated for a GdBCO film in a composite conductor by employing a diffraction technique using synchrotron radiation. The lattIce strain was determined along both the aand b-axes for the orthogonal domains that are generated by the twin structure of GdBCO film. A distinct difference in the 2D strain state that depended on the crystal orientation was revealed for the GdBCO coated conductors. In Gd-I, the lattIce strains along the axial and lateral directions are tensile and compressive under tensile loading, respectively, that is, the 2D internal strain state is anisotropIc. On the other hand, an almost isotropIc 2D strain state was confirmed in Gd-F. In addition, the strain components along the crystal axes in Gd-F are much smaller than the axial strain components in Gd-I. This difference in the internal strain state is attributed to the difference in strain sensitivity between the GdBCO coated conductors with different crystal orientations. The contributions of the strain components along the a- and b-axes to Ic are discussed on the basis of the measured strain sensitivities and internal strains for two conductors. [ABSTRACT FROM AUTHOR]

A superconducting magnetic energy storage system (SMES) for electric power system control has been developed using Yttrium (Y)-based coated conductor of high performance in Ic and mechanical properties, in order to fulfill the requirements for large capacity and cost reduction of the SMES. The target stored energy of the coil required for the SMES system of 100 MVA output power is 2 GJ class. The conceptual designed coil of toroid type consists of one hundred eighty unit coils of 2.8 m outer diameter and each unit coil is connected to each converter of a multi-cell type. Due to this design concept, the main unit coil specifications of 2 kA current, 2 kV voltage, 600 MPa hoop stress tolerance and 3 W/m^2 heat flux around 20 K can realize the SMES system. Coiling technologies have been developing using Y-based wire for SMES. A small multi-layer coil was manufactured and its electromagnetic force characteristics were verified by 600 MPa class hoop stress tests. A bundled-conductor coil of 650 mm class diameter was also manufactured and its current characteristics were verified by 2 kA class large current tests. [ABSTRACT FROM AUTHOR]

Oscillating heat pipes (OHP) for cryogenic use are being developed to improve the heat removal characteristics of high-temperature superconducting (HTS) magnets. It is generally difficult to remove the heat generated in HTS windings, because the thermal diffusivities of component materials decrease with an increase of the operating temperature. Therefore, a local hot-spot can be rather easily generated in HTS magnets, and there are possibilities of observing degradation of superconducting properties and/or mechanical damages by thermal stresses. As a new cooling technology to enhance the heat removal characteristics in HTS magnets, the cryogenic OHP is proposed to be imbedded in magnet windings. The feasibility of cryogenic OHP has been confirmed by fabricating proto-types and by observing stable operations using hydrogen, neon and nitrogen as the working fluid. A high thermal conductivity was achieved that surpasses those of high-purity metals. We also propose a modified-type OHP to mitigate the orientation dependence. [ABSTRACT FROM AUTHOR]

The thermal behavior of a high-temperature superconducting (HTS) coil is significantly different from that of low-temperature superconducting (LTS) coil because it has a greater volumetric heat capacity at the temperature required for practical use. Therefore, the possibility of quench in HTS coils is much lower than that in LTS coils. In the application of the YBCO coil to Superconducting Magnetic Energy Storage (SMES) system, electrical charging and discharging are repeated; therefore, the superconducting characteristics of the YBCO coated conductor may deteriorate as a result of cyclic subjection to tensile strain. To enhance the reliability and safety of HTS coil, protection scheme assuming a quench is also required for HTS coil. In this study, we focus on the coil wound with YBCO laminated bundle (parallel) conductor supposing SMES application and investigate the characteristics of normal-zone propagation and the thermal behavior within the coil during a quench by using a newly developed computer code based on the finite element method and an equivalent circuit. And we also propose a quench detection method using observation of nonuniform current in YBCO laminated bundle conductor and discuss the validity of the detection method comparing with conventional quench-voltage detection. [ABSTRACT FROM AUTHOR]

A multi-laminated HTS tape conductor has been recently developed to fabricate large double pancake coils. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is unbalanced because of different inductances of all tapes. It is very important to analyze current distributions in the multi-laminated tape conductor used for the double pancake coil for SMES. In this paper, we analyze the current distribution in the tape conductor by using electrical circuit model, and then discuss how to obtain the homogeneous current distribution. One way is to transpose the tape position at both ends of pancake coil so as to arrange the tapes symmetrically. However, this method is not perfectly geometrical symmetry for more than 3 laminated tapes in the conductor. We propose new method to obtain homogeneous current distribution by adjusting gaps between HTS tapes in the conductor. Finally we numerically demonstrate the homogeneous current distribution in the 4-laminated tapes with inserting additional thickness among tapes. [ABSTRACT FROM AUTHOR]

We study the electro-magnetic design of 10 MW-class wind turbine generator with high temperature superconducting field winding by using the FEM analysis. The design examples are presented and the generator characteristics are investigated. The 10 MW-class HTS wind turbine generator is considered to be feasible from the stand point of the electro-magnetic design. In this study, 8-pole and 12-pole generators are investigated. From the results, it is considered that the 8-pole design is preferable compared with the 12-pole design. The analysis also reveals the small synchronous reactance of the HTS wind turbine generator. Therefore, proper protection is necessary for the large short circuit current. [ABSTRACT FROM AUTHOR]

Abstract: The cryogenic oscillating heat pipe (OHP) for conduction cooling of superconducting magnets was developed and the function was demonstrated successfully. OHP is a highly-efficient heat transfer device using oscillating flow of two-phase mixture. The working fluids that are employed in the present research are Nitrogen, Neon and Hydrogen, and the operating temperatures are 67–91K, 26–34K and 17–27K, respectively. The estimated effective thermal conductivities from the measurement data of the OHP were higher than one of the solids such as copper at low temperature. These results revealed that the cryogenic OHP can enhance the performance of cooling system for magnets. [Copyright &y& Elsevier]

The thermal behavior of a high-temperature superconducting (HTS) coil is significantly different from that of a low-temperature superconducting (LTS) coil. A HTS conductor has a greater volumetric heat capacity at the operating temperature envisaged for practical applications. Therefore, a HTS coil is much less likely to be quenched than a LTS coil by mechanical disturbances such as the heat generated by the cracking of the impregnation material or by the friction resulting from wire movements. However, the HTS conductor is cyclically subjected to tensile strain because electrical charging and discharging are repeated in real applications involving the Superconducting Magnetic Energy Storage (SMES) system. The superconducting characteristics may locally deteriorate due to this cyclic strain. Therefore, to enhance the reliability and safety of the HTS coil, a quench protection scheme is needed. Because the normal-zone propagation velocity is quite low, detecting a non-recovering normal zone is difficult in HTS coils, and quenching produces excessive overheating that may cause the conductor to melt. In this study, we focus on a coil wound with a YBCO bundle conductor used in SMES applications and investigate the redistribution characteristics of the transport current in and the thermal behavior of the coil during a quench; we use a newly developed computer code based on the finite element method (FEM) and an equivalent circuit. We also discuss a protection scheme to dump the magnetic energy stored in the coils on an external resistance connected in parallel. [ABSTRACT FROM AUTHOR]

We evaluated critical current density and mechanical properties of the Y123 coated conductor (CC) tapes on buffered Hastelloy substrates prepared by the chemical vapor deposition method in high magnetic fields and low temperatures. The Jc values of the tape are about 1.1 MA / cm² at 77.3 K, 0 T and 1.8 MA / cm² at 4.2 K and 17 T for B//c. In addition, the hoop stress test of the single layer coil shows that the stress limit of the CVD-Y123 CC tapes on Hastelloy is over 1 GPa. On the basis of those experimental data, we designed the innermost high temperature superconducting insert coil for upgrading of the 18 T cryogen-free superconducting magnet (18 T-CSM) under the condition of the stress limit of 600 MPa. The coil, which consists of the 22 double pancake coils can generate 9.4 T with the operation current of 295 A in the backup field of 15.6 T. In this case, the central field of the 18 T-CSM can be improved up to 25 T from 18.1 T. [ABSTRACT FROM AUTHOR]

A highly effective cooling technique for a superconducting magnet is proposed by incorporating the cryogenic oscillating heat pipes (OHP) as cooling panels in the coil windings. The OHP is a high performance two-phase heat transfer device, which can transport several orders of magnitude larger heat loads than heat conduction of solids. The cryogenic OHP using H2, Ne, and N2 as working fluids have been developed and tested at the operating temperature ranges of 17-25 K (H2), 26-32 K (Ne), and 67-80K (N2). The measured effective thermal conductivities were reached to 500-3,000 W/m·K (H2), 1,000-8,000 W/m·K (Ne) and 10,000-18,000 W/m·K (N2). The high thermal transport properties of the cryogenic OHP and its application as the cooling components of superconducting magnets are also discussed. [ABSTRACT FROM AUTHOR]

YBCO tapes are expected to be used in future high temperature superconducting (HTS) applications because of their good Jc characteristics at high temperatures and in high applied magnetic fields. In applications to electric power devices such as transmission cables, transformers, and fault current limiters, the HTS conductors will be subjected to short-circuit fault currents that are 10 to 30 times the normal operating current. These over-currents are greater than the critical current, and degrade or burn-out the HTS conductors. Therefore, it is important to clarify the mechanism of the degradation caused by such over-current pulses. We carried out preliminary experiments on damage caused by over-current pulse drive, focusing on the temperature limitation without suffering degradation for over-current pulse operation. A 10-mm-wide YECO tape was cut into 2-mm-wide sample tapes by a laser beam, and the sample tapes were soldered on silver-deposited 100-μm-thick copper plates. Over-current tests were carried out on these sample tapes and Ic degradation was investigated. In addition the contact interface between YBCO and the Ag layer or buffer layer before and after the over-current drives has been investigated in order to clarify the correlation between the degradation and delamination of sample tapes. [ABSTRACT FROM AUTHOR]

The Cu substrates have the advantages of no ferromagnetic contribution to hysteretic AC losses, and low cost compared to Ni substrates. We investigated the Jc - B properties of YBCO films deposited on the cube-textured Cu tapes with intervening buffer layers. A protective Ni overlayer was added on top of the cube-textured Cu tape by electroplating to reduce the oxidation rate of the Cu substrate. The YBCO films prepared on the CeO2/YSZ/CeO2 buffered Ni-electroplated Cu tapes revealed the transport Jc exceeding 3.6 MA/cm2 at 77 K in a self-field. We also confirmed that our Ni-electroplated Cu tape lost its ferromagnetism after 700° C x 1 hour heat treatment. [ABSTRACT FROM AUTHOR]

A textured Cu (100) (001) substrate for practical use in low cost coated conductor applications has been successfully fabricated. A textured Cu substrate is a promising substrate for a coated conductor template. This is the result of a low material cost base, no magnetization loss and good electro conductivity. One of the issues for a Cu substrate is surface oxidation. During REBCO deposition, the Cu substrate is exposed to an oxygen atmosphere, and de-lamination of the buffer layer can occur. To prevent this issue a thin Ni layer was formed on the textured Cu substrate by electroplating. After a further annealing process the Ni electroplated Cu substrates exhibit a good sharp texture and a smoother surface. The eΔΦ and Δω of the substrate were about 4.6 and 4.5 degrees, respectively. The surface roughness was estimated at 6.8 nm Ra by AFM. Using this substrate and clad type Cu/SUS316 substrates, we deposited a CeO2/YSZ/CeO2 layer by Pulsed Laser Deposition (PLD) and an YBa2Cu3O7-δ layer by PLD and Metal-Organic Chemical Vapor Deposition (MOCVD). The results show no occurrence of delamination. Typical critical temperature of the coated conductors was 90.5 K and critical current density was a maximum of 4.5 MA/cm2 (at 77 K in a self-field). [ABSTRACT FROM AUTHOR]

The quality of high-temperature superconductors (HTSs) is rapidly increasing, and they can be used in power systems such as SMES systems and in industries as Si single-crystal growth pullers. In the future, HTS conductors are expected to be used for the magnets in nuclear fusion reactors or accelerators. In such applications, HTS conductors will be exposed to radiation. As a result, HTS conductors become radioactive making the operation and maintenance of the reactors or accelerators difficult; this also leads to an increase in the amount of nuclear waste generated. Therefore, we carry out experiments on the radiation damage in HTS conductors to study the characteristics of HTS conductors in radiation environments and to create an industrial database of the radiation effects on HTSs. We also carry out radioactive analyses on HTS conductors in order to clarify the relationship between the irradiation dose and the activity of HTS conductors. In this study, we prepared YBCO and Bi-2223 tapes and carried out the following preliminary experiments: (a) irradiation of the sample HTS tapes with 2-MeV neutrons at room temperature without transport current and (b) study of neutron-induced radioactivity by gamma-ray spectrometry using a Ge detector after the irradiation. [ABSTRACT FROM AUTHOR]

To achieve large current capacity and mechanical flexibility, high-temperature superconductor (HTS) power transmission cables consist of a number of YBCO coated conductors, which are assembled and wound spirally on a Cu former. In practical applications, superconducting cables might be subjected to short-circuit fault currents that are 10 to 30 times the operating current. Therefore, in order to ensure the stability and feasibility of HTS power cables and protect them from fault currents, it is important to estimate the redistribution of the transport current and electromagnetic coupling among the conductor layer, shield layer, and Cu former. In this study, we carried out experiments on a 20-rn-long YBCO model cable, which was composed of two jointed 10-rn-long YBCO model cables. Over-current with a peak of 31.8 k-Arms and a duration of 2.02 s was applied to the model cable. We performed numerical simulations using a newly developed computer program based on the 3D finite element method (FEM) in order to clarify the electromagnetic and thermal behaviors of the YBCO model cable in the presence of an over-current. [ABSTRACT FROM AUTHOR]

YBCO tapes are expected to be used in future high temperature superconductor (HTS) applications as they have better Jc characteristics at high temperatures and in high magnetic fields. For power applications such as transmission cables, YBCO tapes and a copper former are connected in parallel and they might be subjected to a short-circuit fault current that is 10 to 30 times the normal operating current. Therefore, the over-current behavior, including the hot-spot and the distribution of transport current between the copper-laminated YBCO tapes and the copper former, is very important to examine the stability and feasibility of the cable. This paper describes the experimental results for over-current pulses of a 1-m single-layer cable fabricated with five copper-laminated YBCO tapes and a copper former. Further, we performed numerical simulations by using a newly developed computer program based on the 3D finite element method. [ABSTRACT FROM AUTHOR]

Transport characteristics of IBAD/ CVD-YBa2 Cu3 O7 (YBCO) coated conductor were measured at 4.2 K under hoop stress. The conductor was fabricated by a multi-stage metal-organic chemical vapor deposition (CVD) method. The YBCO layer was deposited on Hastelloy substrate with PLD-CeO2 and IBAD-Gd2Zr2O7 buffer layers. A 20-μm silver layer was sputtered as a protective and stabilizing layer. The hoop stress test coils were fabricated by winding the conductor on a 250-mm diameter stainless-steel bobbin by five turns. Two coils, denoted as coils A and B, were fabricated. The Hastelloy substrate located outside for coil A and inside for coil B. Both coils were teste u magnetic field at 4.2 K under hoop stresses. Coil A and B experienced 1028 and 777 MPa at 11 T, 4.2 K. The measured stress-strain curves provided that the Young's modulus of the conductor was 190 GPa. The tolerable stress of ~1000 MPa and the Young's modulus of 190 GPa are consistent with the values obtained by a tensile test. The hoop stress test results indicates that the YBCO coated conductor is promising for application under huge hoop stress. [ABSTRACT FROM AUTHOR]

Generally speaking for a HTS coil, perpendicular magnetic field to conductor's broad surface should be suppressed as small as possible in relation to the magnetic anisotropy. This is a reason why toroidal coil with relatively many elementary coils is expected for HTS-SMES. On the other hand, from the point of view of the homogenization of critical current distribution in the coil, perpendicular field and parallel field should be balanced corresponding to the ratio of the magnetic anisotropy. This means that a certain level of the perpendicular field is effective to reduce local heat generation in the coil. Furthermore, this concept is especially reasonable for a high-field coil with usual winding method (flat-wise winding) because the perpendicular field does not induce hoop stress which decreases the critical current. In this paper, we show these findings through an optimal design of a MOCVD-YBCO toroidal coil for 2 GJ class SMES taking account of magnetically and mechanically influenced J - E characteristics. [ABSTRACT FROM AUTHOR]

Abstract: We developed equipment to measure AC losses in HTS superconductors subjected to tensile stresses and measured stress dependence of the transport current losses Q t, magnetization losses Q m and total losses Q total in IBAD/CVD and IBAD/PLD YBCO conductors. It was shown by our experiment in the range of stress up to 1–1.1GPa for YBCO conductors that the stress dependences of Q t, Q m and Q total can be predicted by those values at zero stress and stress dependent critical current. [Copyright &y& Elsevier]

For HTS (High-Temperature Superconductor) applications to electric power devices, superconductors are subjected to short-circuit fault currents 10 to 30 times the normal operating current. These over-currents will drive the HTS conductors normal and degrade or burn-out the HTS conductors. Therefore it is important to establish a novel thermal stability criterion for over-current pulse drive. In this study, we carried out preliminary experiments on the damage caused by over-current pulse drive focusing on the limitation of the temperature rise without degradation. We prepared five YBCO sample tapes fabricated with LBAD/PLD and LBAD/ MOCVD methods. Measurements were performed at 60 K and 80 K (Conduction cooling with Gifford-McMahon cryocooler was adopted) in self-field. The experimental results indicated that the degradation of the sample tapes for the over-current pulse with a duration of 1 second depended on not the initial critical current Ic, but the peak temperature Tpeak. The permissible peak temperature without degradation existed at about 400–600 K. The sample tapes were also observed before and after the experiments by magneto-optic (MO) imaging to find the distribution of degradation area. [ABSTRACT FROM AUTHOR]

We investigated the effect of the Ar+ ion beam irradiation on removing NiO on the {100| <001< textured Ni tape surface, and the validity of the ITO as a conductive buffer layer. Excellent biaxial crystal orientations of the CeO2, YSZ and YBCO were achieved in the YBCO/YSZ/CeO2 prepared on the {100| <001< textured Ni tape, by irradiating the surface of the Ni tape before starting the deposition. The Jc of the YBCO/YSZ/CeO2/Ni tape exceeded 2 MA/cm2 at 77 K. We also prepared the biaxially oriented YBCO on the ITO buffered Ni tape. We confirmed that ITO did not react with YBCO, and that ITO aligned biaxially on the {100| <001< textured Ni tape. [ABSTRACT FROM AUTHOR]

Toward the industrialization of YBa2Cu3O7-x (YBCO) coated conductors for practical applications; metal-organic chemical vapor deposition (MOCVD) has been investigated. We applied multi-stage MOCVD to achieve high-speed production of coated conductor because the increase of the number of depositing stages placed in a line could enlarge deposition area. Using 12-stage CVD, we succeeded in deposition of highly biaxially oriented YBCO layer at tape transfer speed of 50 m/h on the CeO2 capped ion-beam-assisted-deposition (IBAD) — Gd2Zr2O7 (GZO) buffered Hastelloy tape, and achieved high critical current density (Jc) exceeding 2 MA/cm2 in a short sample. And it was found that lowering substrate temperature according to YBCO layer growth was effective to increase Ic. Using this method, high critical current (Ic) of 174 A was achieved by 1 μm thick YBCO layer which passed through 12-stage CVD, and 227 A by 1 μm thick YBCO layer deposited by 6-stage one. Based on these results, three 200 m-class YBCO layers were deposited by multiple depositions at tape speed of SO m/h each, using the 12-stage CVD system. A 203 m-long YBCO layer was successfully deposited with end-to-end Ic of 92.8 A, so that the multiplication of Ic and length reached 18.8 kA · m. These results indicate that a multi-stage CVD technique is useful for a rapid fabrication of long YBCO coated conductor. [ABSTRACT FROM AUTHOR]

YBCO coated conductors have been expected to be applied to superconducting magnetic energy storage (SMES) due to high critical current density under high magnetic field and possibility of reducing cooling cost. Solder joints are essential to fabricate a high Tc superconducting coil for SMES system which requires long length of coated conductors. Not only low joint resistance but sufficient mechanical strength is needed, since conductors are exposed to large electromagnetic force generated by large transport current and high magnetic field. In the present study, influence of tensile load on transport property through the joint was investigated. The solder joint with sufficiently low resistance of 5.3 nΩ was attained before loading. Such joint can carry the load up to 650 N without substantial degradation. For further applied load, degradation attributed to fracture at the edge of the conductor is firstly observed. Overall fracture is caused by delamination at the interface between YBCO and CeO2. As a result, importance of interfacial strength between the superconducting and buffer layer is revealed to realize both low joint resistance and mechanical strength for solder joint. [ABSTRACT FROM AUTHOR]

A testing coil composed of six pancake-coils with a YBCO coated conductor has been fabricated and its superconducting properties have been investigated. The resulting coil has generated magnetic fields up to 0.65 T at 65 K in zero external magnetic field. In order to enhance capability for transporting current of YBCO coil, superconducting behavior of the multi-tape YBCO conductor has also been investigated. The critical current of the conductor that is formed by bundling two tapes has practically achieved the sum of the critical currents. [ABSTRACT FROM AUTHOR]

High Tc superconducting (HTS) toroidal coil using YBCO coated conductor is designed for 70 MJ class superconducting magnetic energy storage (SMES) for power system control. Its configuration and shape are optimized by means of genetic algorithm (GA) to minimize the required length of the conductor. The optimization is performed for two kinds of constrains, i.e., maximum electric field or flux flow loss of the coil, which are calculated by means of finite element method (FEM). The FEM analysis considers quantitative current density (J)-electric field (E) expressions based on percolation transition model. It is shown that the great transport performance against magnetic field of YBCO coated conductor can realize a very compact SMES coil compared with an existing Nb-Ti's one. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the thermal runaway characteristics of a conduction-cooled Bi2212 HTS coil with a 4 K-GM cryocooler system under compensating operation for load fluctuations. We measured the temporal evolutions of temperature and voltage distributions of the HTS solenoidal coil for typical current patterns of load fluctuation compensation at different ambient temperatures. On the basis of these experimental results, we constructed a thermal analysis model, and analysed the thermal runaway characteristics during and after the load fluctuation compensation. Based on the results of our experiments and the numerical simulations, we proposed criterion for the monitoring of an HTS SMES system during compensating operation for load fluctuations. [ABSTRACT FROM AUTHOR]

AC losses in power transmission cables composed of coated conductors could be potentially small. A strategy to approach their potentially small AC loss was studied. AC losses in mono-layer conductors for cables were calculated numerically in order to show the principle for AC loss reduction: use of narrower coated conductors and/or decrease in space between conductors reduce the magnetic field component perpendicular to the wide face of coated conductors, and they are effective for AC loss reduction. This principle was confirmed experimentally by using short monolayer conductors. Based on the principle, 1 kArms-class three-layer conductors were fabricated, and AC loss of 0.054 W/m at 1 kArms was achieved in a three-layer conductor whose outer diameter is 19.6 mm. The influence of a magnetic substrate on the AC losses in a single coated conductor and a mono-layer conductor for a cable was studied numerically. [ABSTRACT FROM AUTHOR]

Abstract: We have designed and operated a rotating-magnet type AMR (active magnetic regeneration) refrigerator that uses water as a heat transfer fluid. Four kinds of gadolinium-based alloy are used as magnetic materials. A magnetic field of 0.77T is applied by neodymium permanent magnets. The refrigerator produces a maximum cooling power of 60W around 10°C. An optimal time for one cycle exists, and it depends on the water flow rate and the frequency of magnetization and demagnetization. Enhancement of the water flow rate and the frequency is known to be essential for increasing the cooling power of this refrigerator. [Copyright &y& Elsevier]