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We investigate the rotational characteristics of a 50-kW-class high-temperature superconducting induction/synchro- nous motor in superconducting and non-superconducting states. The prototype motor was first placed in liquid nitrogen, and the efficiency contour was obtained. The liquid nitrogen was then gradually removed from the motor under the partial load (10 kW) condition. This showed that continuous operation is possible even at temperatures exceeding 130 K. Furthermore, we succeeded in driving at 11% of the rated output, even at room temperature. As a result, a practical high-temperature superconducting motor that can continue to operate with reduced output even when the cooling system fails could be realized.

We have developed a diagnostic method for monitoring core position and strand failure in DC superconducting cable. DC superconducting cable has been expected for various uses such as HVDC, railway feeding, etc. On the other hand, diagnostics is indispensable for its practical operation. In particular, knowing core position in cooling process is important because the position significantly influences the thermal invasion from outside. Furthermore, detecting strand failure is also crucial as a presage of a significant fault. This can be performed by measuring stray field distribution changed by such situations. An apparatus, which can be clamped on the outer (corrugated) pipe of the cable, was fabricated with an array of multiple Hall sensors. As a result, the position of the core was successfully estimated with the accuracy of 1 mm. Furthermore, one strand failure among 16 strands was also successfully detected. We believe that this method will be a promising technique for diagnostics for DC superconducting cables.

We have investigated spatial distribution of local critical current density ( J c) in a Co-doped BaFe2As2 (Ba122:Co) film based on scanning Hall-probe microscopy (SHPM). In-plane J c distribution was derived from the magnetic field distribution. Thanks to the high-resolution characterization, local obstacle can be detected clearly, as well as a local spot with extremely high J c over 7 MA/cm2, which is among the highest value at remanent state reported for this series of films so far. The SHPM allows us to separate the influence of current blocking obstacles and intrinsic flux pinning properties on J c. Validity of the J c analysis was checked by a magnetization measurement based on a SQUID magnetometer. Moreover, we investigated the J c distributions at different temperatures by SHPM and studied their probability distribution functions (PDFs). PDFs are found to be scaled by a Weibull function with the same shape parameter, while J cs are decreasing with higher temperature. These results indicate that the intrinsic in-plane pinning is controlled by the same mechanism.

Research and development for the practical application of a medical-use magnetic resonance imaging system (MRI) superconducting magnet that does not require liquid helium started as the New Energy and Industrial Technology Development Organization's (NEDO) supported project in fiscal 2016. Development of a liquid helium-free medical MRI superconducting magnet has been desired. Another purpose is to reduce the size and weight of high magnetic field magnets. By using the high temperature superconducting coil, it is possible to make the 3T magnet of the same shape, weight, leakage magnetic field as 1.5T magnet. In this project, we are developing a half size active shield-type 3T REBCO coil for MRI. This magnet has active shield coils with a maximum diameter of 1200 mm, and its room bore diameter is 480 mm. This magnet is one of the world's largest magnets using a REBCO wire with an accumulated energy of 1.6 MJ at the rated magnetic field. It generates a magnetic field of high homogeneity and stability necessary for imaging. In this paper, we report the half-size active shield-type 3T coil and its cooling system that can reduce the initial cooling time by thermal switches.

It has been recognized as a significant issue that the magnetization of RE-123 coated conductors affects the spatial homogeneity and the time variation of the magnetic field of the magnets for MRI, NMR, and accelerators. Therefore, the understanding and the modelling of the magnetization of a coated conductor are crucial for the quantitative estimation and the compensation of its influence on a magnet. On the other hand, the magnetization of the coated conductor has been usually measured and analyzed as a global value; then it is difficult to clarify the local electromagnetic behavior governing such a global performance. Furthermore, such behavior should be investigated under the condition not only with external magnetic field but also with DC transport current as is exposed in a magnet. In this study, the magnetization of a coated conductor was characterized by a spatially-resolved measurement based on the scanning Hall-probe microscopy (SHPM). The magnitude and the time variation of the magnetization were clarified from the visualized magnetization current distribution and its time variation. In particular, they were modeled successfully including the influence of the transport current. Furthermore, taking account of the findings, the experimental results were successfully reconstructed by a numerical analysis based on finite element method (FEM). This will contribute to the quantitative estimation and the compensation of the magnetization problem for the magnets comprising RE-123 coated conductors.

This paper proposes a superconducting cable with energy storage function crucial for large-scale introduction of renewable energies to electric power system. The compensation for the power generation fluctuation from renewable energies has been one of the most critical issues for large-scale introduction of them. It will become difficult to manage that only by conventional energy storage devices because high-power and high-speed compensation is necessary especially for large-scale photovoltaic (PV) power generation. The power system with the proposed superconducting cable will overcome the problem. Such a project started in 2017 in Japan with the support from the government. The target is 10 MW and 10-km-long superconducting cable with the stored energy of 1 GJ in 2050. We have designed such superconducting cable, and have carried out simulations assuming 10-MW-class PV power generation. As a result, very severe fluctuation from PV could be compensated only by the superconducting cable without any batteries. This indicates that the power system itself had energy storage function which could only be realized using superconducting technology. We believe that this new system will be a key solution for future large-scale introduction of renewable energies, and will dramatically expand the market for superconducting technology.

A new metal organic deposition (MOD) process using precursor solution containing metal trifluoroacetates was developed to improve in-field performance. In this process, the pinning centers of BaMO3 (M: metal elements such as Zr and Hf) materials could be made to be finer by reducing the once coating thickness in the coating and calcination step. This is referred to as the ultra-thin once coating (UTOC)-MOD process. This process improves the in-field performance. The UTOC-MOD process also has the advantage of uniformity of 2-dimensional Jc-distribution, which was determined using a scanning hall-probe microscopy analysis. Improvement of the Jc uniformity was also confirmed based on scribed tapes. A smaller dispersion of the filament-critical current values in the UTOC-MOD tape was determined based on a comparison with the results for obtained by a conventional process. With respect to the mechanical strength, it was established that the dispersion of the delamination strength, which was evaluated using stud-pull equipment, was suppressed. Microstructural analysis revealed that, the UTOC films were pore-free, although large pores are present in the films when conventional MOD is utilized. This difference in the microstructure can be attributed to the aforementioned improvement in the uniformity of the UTOC-MOD films.

REBa2Cu3Ox (REBCO, RE = rare earth) coated conductors (CCs) are promising as superconducting wires for high-field magnets because of their high in-field critical current density (Jc) performance and high tensile tolerance. Fujikura, Ltd., has been developing BaHfO3 (BHO)-doped EuBa2Cu3Ox (EuBCO, Eu = Europium) CCs using a hot-wall-type pulsed-laser deposition (PLD) in order to further improve the in-field performance. Although a high deposition rate in the PLD process is necessary for mass production, it has been found that the in-field performance greatly differ depending on the deposition rate. In this study, flux pinning properties of BHO-doped EuBCO CCs fabricated with different deposition rates by the hot-wall PLD on IBAD substrates were investigated in detail. From the scaling characteristics of the flux-pinning force density (Fp) curve, the BHO precipitates in a fast deposition rate REBCO film appeared to behave like random pinning centers, which was almost consistent with a result of transmission electron microscope observation. On the other hand, from a decrease of anisotropy in the magnetic field angle dependence of Jc, it was also confirmed that BHO precipitates were not completely random pinning centers, that is, it has some kind of anisotropy. Considering the critical current value per production time, it was also found that the fast deposition rate is advantageous since the REBCO layer could be thicker.

Fujikura Ltd., Chiba, Japan, has developed stable and high-throughput production techniques for REBCO coated conductors (CC) by using large-area ion-beam-assisted-deposition (IBAD), and hot-wall type pulsed-laser-deposition (PLD). Recently, we have been attempting to dope BaMO 3 (BMO, M: Zr or Hf) to REBCO layer in order to enhance in-field critical current density (J c ). In the course of optimizing deposition conditions of PLD for BaHfO 3 doped EuBCO films on IBAD templates, “high J c condition” and “high growth rate condition” were found. For samples prepared under these conditions, the magnetic field angle dependence of I c and REBCO thickness dependence were investigated. Finally, we succeeded in fabricating a 300-m-long CC with uniform I c distribution at the high-growth-rate condition. The longitudinal I c homogeneity (defined as standard deviation divided by average) at 77 K evaluated by magnetization method was 2.6%, which is comparable to nondoped conductors. Transport in-field I c for the both end points were 1756 and 1786 A/cm at 30 K, 2 T, respectively.

We have investigated transient behavior of RE-123 coated conductors in fault current limiting operation based on experimental hardware-in-the-loop simulation (HILS). Fault current limiting function of superconducting electric power application is attractive to maximize the potential of power system; such a function can be realized by the transition to the resistive state of superconducting wire. However, the phenomena is relatively complicated: nonlinear current transport properties varying with time-dependent temperature rise. Furthermore, from practical point of view, the influence of spatially homogeneity of cooling and local critical current properties in RE-123 coated conductors must be clarified for reliable operation. To demonstrate this, we developed HILS system using real-time digital simulator. Fault current limiting operation was successfully demonstrated for dc electric railway system. This method enabled us to evaluate the real-time responses of RE-123 coated conductors such as nonlinear properties and thermal behaviors under a power grid network. In particular, we applied RE-123 coated conductors with spatially inhomogeneous cooling and local critical currents to the experiment to understand the influences of them on the fault current limiting and recovery functions. Furthermore, such transient phenomena were successfully described by an electrically and thermally coupled analysis taking into account of temperature dependent nonlinear transport properties of the RE-123 coated conductors based on the percolation transition model. The method and findings will become crucial for effective and reliable designs of superconducting fault current limiters.

We investigated the relationship between current capacity and local critical current distribution of a Cu-sheathed multifilamentary RE-123 coated conductor (CC). Patterning multifilamentary structure on CC will be a promising solution for reducing magnetization to assure spatial homogeneity and its temporal stability of magnet applications such as MRI and NMR. On the other hand, it will become more difficult to maintain the current capacity because a smaller defect can block the current flow in a narrower filament. Permitting electrical coupling among the filaments will work for maintaining current capacity because current can avoid such a defect by flowing into the adjacent filament. However, too small interfilamentary resistance will result in long time constant of filament coupling, which will affect spatial homogeneity and its temporal stability of magnet applications. Therefore, to design a multifilamentary CC satisfying the requirement from magnet applications, it is necessary to understand the quantitative impact of interfilamentary resistance of the multifilamentary CC on its current capacity under the influence of spatial variation of local critical currents. In this study, we estimated global critical current of a Cu-sheathed multifilamentary CC as a function of interfilamentary resistance by considering its local critical current distribution in each filament. As a result, it was confirmed that the electrical coupling among the filaments was very effective to improve the current capacity of such a multifilamentary CC especially for a section with spatially inhomogeneous local critical currents. Furthermore, it was also found that local heat generation could be significantly suppressed even for a section with relatively homogeneous local critical currents.

We have investigated the in-field critical current properties in BaZrO3-added (Y, Gd) Ba2Cu 3O7-δ (YGdBCO)-coated conductor fabricated by using a multi-coating trifluoroacetates metal-organic deposition (MOD) method. We compared these properties with EuBCO-coated conductor fabricated by the pulsed laser deposition (PLD) method. The sample using the 30-nm once-coat-layer-thickness d once shows superior in-field J c down to 4.2 K than that of the previous standard coating using 170–nm-thick layer for each coating. From the analysis of E – J characteristics, an analytical expression for J c as a function T and B has been derived. It was confirmed that the high J c region in sample with d once = 30 nm is widely spread in high-temperature and high-magnetic-field region. By comparison with the J c properties of the BaHfO3 -added PLD CCs, the minimum J c, which is estimated from magnetic field angle dependence, shows even higher value up to 5 T of magnetic field at 65 K and up to 3 T at 77 K. From these results, the new MOD-YGdBCO process using the thin once-coat-layer-thickness is very promising for the practically important mid field region such as 3 to 5 T.

BaMO 3 (BMO, M: Zr or Hf)-doped REBCO-coated conductors were prepared by Hot-Wall PLD method on IBAD template. The highest J c was obtained for BaHfO 3 -doped EuBCO. Quite strong pinning force density (F p ) of 1.6 TN/m 3 was observed at 4.2 K, 15 T, for a sample deposited with growth rate of ~5 nm/s. It had strong c-axis correlated pinning at the temperature above 20 K with the matching field of ~5 T. A 45-m-long sample was formed by productive high growth rate over 20 nm/s, being consistent with commercial nondoped conductors. It had also large I c of 1687 A/cm and F p of 0.96 7 TN/m 3 was obtained at 4.2 K, 15 T. The end-to-end longitudinal Ic homogeneity (σ) at 77 K in low field was evaluated to be 2.2% by magnetization. Transport in-fields I c were also measured for the both end points at 30 K, 2 T, resulting in 1863 and 1883A/cm, respectively.

We have carried out the characterization of local critical current distribution in a 113-m-long multifilamentary coated conductor (CC) based on reel-to-reel scanning Hall-probe microscopy. Patterning multifilamentary structure on CCs is a key technology for the reduction of ac losses due to magnetization. Recently, this advantage has also been expected for the reduction of the magnetization in a coil winding which has been recognized as a critical problem for HTS magnet applications such as accelerators, MRI, and NMR from the viewpoint of field homogeneity and temporal stability. However, it has been difficult for the conventional techniques such as four-probe method, TAPESTAR, etc., to make diagnostics for multifilamentary CCs due to the limitation of spatial resolution. On the other hand, our measurement has an advantage in taking two-dimensional field image. This enabled us to confirm that multifilamentary structure as well as the corresponding magnetization reduction was successfully achieved in a long-length CC. At the same time, by the estimation of local critical current distribution for each filament, it was also found that there were still some local defects, which affected the global performance of the multifilamentary CC, even if the probability density of such defects was only in the order of 10 -5 . These findings will become crucial information for the optimization of fabrication processes of multifilamentary CCs and for their nondestructive quality assurance.

REBa2Cu3Ox (REBCO, RE = rare earth) coated conductors (CCs) are expected to show high performance for superconducting coil applications due to their high tensile strength and high critical current density under magnetic fields. One of the most serious problems on the coil application is the significant screening current, which is caused by the configuration of CC. Since screening current is dependent on the width of the REBCO layer, filamentization of the REBCO layer is strongly desired. We have succeeded in fabricating long length four-divided multifilamentary CCs with 4 mm wide over 100 m long by using the process of scratching the IBAD-MgO layer (scratching process). In this work, we fabricated two epoxy-impregnated coils and investigated the effects of the screening current. One of the coils is wound with multifilamentary CCs fabricated by scratching process, another is wound with conventional mono-filamentary CC. As the results, it is confirmed that the screening current is reduced and the coupling current between the filaments might be in the acceptable range on the DC magnet application.

We have investigated flux flow dissipation in typical two kinds of HTS tapes, i.e., a Bi-2223 multi-filamentary tape and a RE-123 coated conductor (CC) from the view point of heat load under over current conditions. Based on systematic measurements on current-voltage characteristics, the nonlinear flux flow dissipation has been described analytically by taking into account current sharing in metallic sheath or stabilization layer. Flux flow dissipation in the RE-123 CC shows much steeper temperature dependence than that of the Bi-2223 tape. As a result, attainable cooling power becomes smaller in the RE-123 CC in comparison with that of Bi-2223 tape even if the same cooling condition. In other word, acceptable temperature rise in the RE-123 CC is small at over current condition, whereas moderate temperature dependence in the Bi-2223 tape allows stable operation even if the bias current exceeds the critical current. Influence of spatial inhomogeneity in the both HTS tapes has also been investigated. Longitudinal variation of local critical current, Ic, and its statistical behavior have been characterized by use of reel-to-reel scanning Hall probe microscopy. It has been found that the flux flow dissipation is possibly localized more than one order higher than that of the average value due to discrete local Ic drops.

A method for making multi-filamentary REBCO tapes by only scratching buffer layer was developed for coil application which requires accurate magnetic fields. By continuous I c measurement, we found that our new multi-filamentary tape could provide almost equal I c compared to conventional tapes. Then, using EBSD and RTR-SHPM methods, a divided structure of REBCO layer was surely confirmed. AC loss was also decreased. Furthermore, the result of delamination test of our new multi-filamentary tape showed enough mechanical property. As a result, we have succeeded in developing 100 m class multi-filamentary tape for superconducting coil.

We have developed a hardware-in-the-loop (HIL) simulation setup to analyze superconducting devices for dc electric railway systems. When such superconducting devices are to be installed into a larger system, it is indispensable to characterize their behavior, i.e., their interaction with the system, to assure their reliability in all operating conditions. This is challenging when using full-scale superconducting devices and real power systems because many types of operation and fault cannot be easily demonstrated. Numerical simulation may compensate for that, but complete modeling of superconducting devices has often been difficult because of complicated electromagnetic behavior due to nonlinear transport properties, the transition between superconducting and normal states, and so on. In this paper, we have established an HIL simulation setup by the combination of superconducting hardware and a real-time digital simulator (RTDS). They communicate information about the instantaneous current and voltage values to each other every 50 $\upmu$ s. This enables us to simulate the interaction between superconducting devices and the system for many kinds of operation and fault. Furthermore, it is not necessary to use a full-scale superconducting device, as the signal level from/to the RTDS can be scaled. This will be very attractive for understanding the behavior of a superconducting device by studying a small prototype before developing the full-scale one.

For the further development of MgB2 wires, investigation of 3-D structures for MgB2 filaments and sheath materials is important. However, typical cross-sectional observation such as optical microscopy and scanning electron microscopy are essentially 2-D, therefore, not enough to understand the 3-D filament structures. In this paper, we have adopted X-ray microtomography and carried out a 3-D analysis for MgB2 wire. X-ray microtomography (Skyscan 1172, Bruker) allows us to visualize the internal filament structure of a centimeter-long MgB2 wire with a high spatial resolution of 1.1 $\mu\text{m}$ , with a nondestructive manner. We investigated the boundary between the sheath material and the MgB2 filament of an internal Mg-diffusion-processed MgB2 wire. Furthermore, by improving the signal-to-noise ratio for the X-ray microtomography, we have also identified the boundary between the MgB2 filament and the hole (air) in spite of the low X-ray absorption coefficient for boron and magnesium. From the 3-D analysis, we can reveal the shape and area of MgB2 filament quantitatively and also their statistical distribution.

We have developed a method for the nondestructive characterization of critical current distribution in MgB 2 wires based on magnetic microscopy. This method enables us to evaluate critical currents of MgB 2 wires, even in the condition where they become too large to be measured by the conventional four-probe transport method from the viewpoint of heat generation and/or the limitation from the measurement system. Furthermore, the inhomogeneity in local critical currents in the wires can be also estimated, while it is difficult for the conventional magnetization method, using a SQUID magnetometer. In this paper, by overcoming the influence of magnetic sheath materials, which are widely used for recent high-performance MgB 2 wires, we have succeeded in developing a nondestructive method for the characterization of longitudinal distribution of local critical currents in them. This method will become a fundamental technique for a nondestructive product testing at the stage of full-fledged commercial production in the future.

This paper reports a diagnostic method for clarifying performance bottlenecks of superconducting wires and tapes for their further performance enhancements. In particular, our achievements by scanning Hall-probe microscopy (SHPM), which worked well for selecting positions for microstructure observation by SEM, TEM, and X-ray CT, are introduced. This hybrid microscopy offers the information of direct relationship between the performance of a practical-scale superconducting wire or tape and its origin in micro-scale or nano-scale structure. As such examples, characterization results for an MgB2 multi-filamentary wire, a commercially available long RE-123 coated conductor, and a striated multi-filamentary coated conductor are reported in this paper through reviewing our past studies.

VAMAS TWA 16 promoted an international round robin test (RRT) on critical current (I c ) measurement of RE-BaCu-O (REBCO; RE = rare earth) superconductors to establish the transport I c measurement method in liquid nitrogen bath without an external magnetic field. Ten laboratories from five countries participated in the RRT and tested commercially available REBCO superconductors. I c and measurement conditions were reported. In parallel, intrinsic I c nonuniformity of the superconductors were evaluated by reel-to-reel scanning Hall-probe microscopy for 10-m conductors. Statistical analyses of I c provided uncertainty of the measurement method. Combined standard uncertainty was analyzed considering the intrinsic nonuniformity of I c . The analysis indicated that the intrinsic nonuniformity has the largest contribution to the uncertainty of I c .

With technological advance of the REBaCuO (RE: Rare Earth elements, REBCO) coated conductors (CC), development of the superconducting applications for its practical use has been carried out recently in various fields. In addition, improvement of the magnetic properties of REBCO CCs makes superconducting devices feasible in the liquid nitrogen. The higher Ic values are required in high magnetic fields by the viewpoint of the requirement in conjunction with the superconducting CCs. Therefore the improvement of the Ic values in the magnetic fields is one of the most important problems to apply them to a device (e.g., NMR, MRI, others). In this work, we investigated the fabrication processing to improve the in-field properties of the YGdBaCuO (YGdBCO) CCs by introduction of artificial pinning centers (APCs). The TFA-MOD method using the batch type furnace for the conversion reaction as a cost effective process to fabricate REBCO CCs was improved by adopting the interim heat treatment during the ramp step of the conversion reaction. The improvement of the properties by the improved process was remarkable and the advanced CCs were named as nPAD-YBCO. A 124 m-long nPAD-YBCO consisted of YGdBCO CC with BZO nano particles was successfully fabricated, exhibiting the I cmin > 50 A/cm-w @77 K, 3 T (I c : Critical current) throughout the conductor. Analyzing the characteristics of the conductor, the BZO particles introduced into the YGdBCO layer worked as effective APCs in wide ranges of temperature and magnetic fields.

We have investigated the influence of self-field on the critical current density distribution in a Bi-2223 tape and its effect on the current capacity of an assembled conductor. Critical current of a tape is usually measured by four-probe transport method under self-field. On the other hand, the critical current of an assembled conductor cannot be simply summed because the tape experiences different condition of magnetic field due to the interaction among the tapes. To quantify the situation, it is necessary to clarify first how the critical current of a tape is determined at the self-field and then to consider the interaction among the tapes. In this study, it was found that the distribution of critical current density was largely influenced by local magnetic field inside the tape. The results were quantitatively described by a model considering the position dependence and magnetic field dependence of local critical current density. Using such a quantitative model, we numerically investigated the current capacities of assembled conductors with different arrangements of the tapes.

We have investigated the current transport properties of batch furnace processed TFA-MOD Y x Gd 1-x Ba 2 Cu 3 O y (YGdBCO) coated conductor (CC) doped with nanoscale BaZrO 3 artificial pinning centers (APCs). As the comparison with those of previous processed YGdBCO CC, it has been confirmed that the present process is very effective to improve current carrying performance of the CC at not only high-temperature but also low-temperature region, for example, the I c at 4.2 K and 17 T is 450 A/cm-w, i.e., the engineering J c is 4.3 × 10 8 A/m 2 , which is comparable value to that of Nb 3 Sn wire at 4.2 K. In addition, angular dependences of the I c clearly show the effectiveness of the APCs. Namely, the minimum I c in the whole angle region at 77 K, 3 T increase from 7 to 35 A/cm-w, and the anisotropy of I c is reduced. We will also discuss the analytical expression of in-field current transport property based on the percolation transition model and the scaling law of the flux pinning. By using this analysis, electric field versus current density characteristics in arbitrary conditions of temperature and magnetic field can be described, and also, the statistical distribution of J c can be estimated. These results are important not only for the design of superconducting devices using CCs but also for understanding the pinning properties.

We have investigated current transport properties in two G 1 dBa 2 Cu 3 O 7-δ (GdBCO) coated conductors deposited on different quality of IBAD substrate, i.e., in-plane alignments of the substrate are 1.98° and 2.78°, respectively. From the comparison, J c enhancement has been confirmed in wide temperature and magnetic field region in the sample using highly oriented IBAD substrate, whereas the irreversibility field and shape of pinning force density ( F p ) does not change much. Furthermore, higher in-filed J c than that of BaHfO 3 doped GdBCO coated conductor deposited on standard IBAD substrate has also been observed in practical high field region at low temperature. These results indicate that the improvement of in-plane texturing in the substrate is still very effective even in such range of 2 to 3° to improve in-field J c .

We have investigated electric field vs. current density( E-J ) characteristics of Gd 1 Ba 2 Cu 3 O 7-δ coated conductor over a wide range of E by deriving from magnetization relaxation and transport four-probe measurements. We succeeded in obtaining E - J characteristics between10 -2 to 5×10 −11 V/m, and analyzed the results within a frame work of the percolation transition model taking into account flux creep with a distribution of activation energy. This allows us to describe E - J characteristics as well as magnetic relaxation analytically based on the transport measurements. Clear deviation from the n -value model has also been confirmed from the experimental results.

The five-year national project in Japan for RD a high in-field minimum Ic value over 54A/cm-width under 3T at 77K was realized in a 200m long EuBCO tape with artificial pinning centers of BaHfO3 by the pulsed laser deposition (PLD) technique on the IBAD template. On the other hand, the AC loss reduction was confirmed in the tapes fabricated by both PLD and the metal organic deposition (MOD) techniques by scribing 100m tapes into 10-filamments. Additionally, the mechanism of the delamination phenomenon was systematically investigated and the strength was improved by eliminating the origins of the weak points in the films. Through the development, all targeted goals were accomplished and the several results were appreciated as a world champion data.

We have succeeded in characterizing local critical currents and electromagnetically equivalent widths of slit coated conductors (CCs) as a function of their longitudinal position based on reel-to-reel scanning Hall-probe microscopy (RTR-SHPM). The aim is to make a quality control of slit CCs intended for electric power application, such as electric power cable in particular, for ac losses reduction. Long pieces of slit CCs, i.e., collectively 40-m-long pieces of 2-mm-wide slit CCs, were transferred in their longitudinal direction, and continuously magnetized in a liquid nitrogen bath; the magnetic field distributions of the samples were then measured by scanning a Hall sensor. From the magnetic field distributions, we could evaluate local critical currents and the equivalent widths of the slit CCs as a function of their longitudinal position. The difference between the equivalent width and the geometrical width of a CC corresponds to the damage due to the slitting process. This means that we can discuss such damage precisely together with its statistics along the longitudinal direction. This kind of diagnostics will be a very powerful technique for establishing slitting processes for producing narrow CCs for overcoming the issue of ac losses for electric power application comprising CCs.

TFA-MOD derived YBCO tapes are expected for many applications due to cost-efficiency. In some applications, uniformity and mechanical strength are required for tapes. A 205 m-long YBCO tape was fabricated with high and uniform I c performance throughout the tape by adopting the interim annealing before the conversion process. The effect of the interim annealing on the crystal growth mechanism of YBCO has been studied focusing on the relationship between the interim annealing conditions and delamination, in this work. Delamination strength was evaluated in the samples prepared with and without interim annealing by the stud pull method. Measurements were carried out on 50 different points for each sample and the results were analyzed statistically. The difference between the two samples was remarkably seen in the delamination strength below 60 MPa. The conventionally annealed sample had more points with low delamination strength below 60 MPa than the interim annealed one. The cross sectional images of both samples observed by SEM showed that there were few pores within the interim annealed superconducting layer, although conventional superconducting layer had many pores. These results suggest that the pores within YBCO layer might be origins to be propagated for delamination at low strength.

Long REBa2Cu3Ox (REBCO, RE: rare earth element) coated conductors with BaMO3 (BMO, M: metal) doping have been expected for the industrial and commercial applications. It is known that critical current (I c) of REBCO coated conductors (with or without artificial pinning centers doping) in magnetic field at high temperature is superior to the other superconducting wires. Especially, we have found that EuBa2Cu3Ox (EuBCO) coated conductors with BaHfO3 (BHO) doping show higher critical current density (J c) and I c at high temperature in self and magnetic fields than those of YBa2Cu3Ox and GdBa2Cu3Ox coated conductors with BHO doping. However, in order to realize EuBCO coated conductors with BHO doping for various applications such as an armature coil, the much higher uniformity of not only longitudinal and but transversal I c distributions of long REBCO coated conductors with high in-field performance for filamentary structure is required. The plane-plume PLD (pulsed laser deposition) method is performed by shortening the target-substrate distance and increasing the number of plumes with scan of X-Y axes directions to increase the deposition rate and averaging the deposition conditions which should relate to obtain the uniformity I c distributions. We fabricated the EuBCO coated conductors with BHO doping (of 0.6 m length and 10 mm in width) by the combination of the ion-beam assisted deposition (IBAD) and the plane-plume PLD method and then we processed the multi-filamentary structure EuBCO coated conductors with BHO doping (of 8 filaments of 440 μm, 0.6 m in length and 5 mm in width) by using the excimer laser scribing to reduce the AC loss and to control the shielding current. I c distributions in a width direction of this EuBCO coated conductor with BHO doping was improved as an uniformity of filament-I c of 4.3 %. Recently, we fabricated the 16 filamentary and 3 m long EuBCO coated conductor with BHO doping by IBAD / plane-plume PLD method. We confirmed that the hysteresis loss was reduce to 1/16 by a 16 filamentary EuBCO coated conductor with BHO doping comparing with EuBCO coated conductor with BHO doping without filamentation.

In this study, we investigated the correlation between microstructures and critical current density (Jc) of YBa 2 Cu 3 O 7− X (YBCO) films with BaZrO 3 (BZO) pinning centers by introducing holding temperature during the crystallization process. Smaller BZO particles and higher in-field Jc were found in the YBCO film with holding temperature than the one without. As a result, films with improved microstructures were successfully fabricated by implementation of additional process, holding temperature, and highly in-field Jc were obtained by introducing smaller BZO particles as artificial pinning centers.

Joint techniques are important to manufacture long superconducting tapes. It has been reported that GdBa2Cu3Oy (GdBCO) coated conductors have higher critical current and critical temperature than YBCO. However, it was reported that the joint resistance of GdBCO was found higher than that of YBCO. In this paper, the elemental distribution maps were investigated to examine the cause of joint resistance. Electron microscopy analysis of GdBCO showed the reduction of oxygen in GdBCO layer. This oxygen reduction may cause degradation of superconducting properties and increase of Ag-GdBCO interfacial resistance, which may have led higher joint resistance in Ag/GdBCO.

We have been developing long REBa2Cu3O7-δ coated conductors with high performance by the combination of the IBAD and the PLD methods. To realize the low production cost for REBa2Cu3O7-δ coated conductors, growth conditions were optimized for long tape fabrication in the “in-plume PLD method”. As a result, the Ic performance was confirmed with a high production rate under the high oxygen gas pressure and high laser energy density of > 800 mTorr and > 3 J/cm2, respectively. We successfully fabricated a 35 m long GdBa2Cu3O7-δ coated conductor with high Ic value of 619 A/cm-w by the production rate of 30 m/h.

Pure Cu (99.99%) is processed by equal-channel angular pressing (ECAP) and by high-pressure torsion (HPT). The electrical resistivity aswell as the microhardness increases with an increase in the equivalent strain at an early stage of straining, but saturates to a steady state at theequivalent strains more than ³20. At the steady state, the samples processed by ECAP and HPT show a significant increase in the hardness(³270%) but little decrease in the electrical conductivity (³12%) when compared to the annealed state. Transmission electron microscopyconfirms that the microstructure does not change at the saturated level with further straining. Evolutions of hardness, electrical conductivity andmicrostructures are also investigated after post-HPT annealing. [doi:10.2320/matertrans.MD201109](Received June 30, 2011; Accepted August 9, 2011; Published September 21, 2011)Keywords: severe plastic deformation, equal-channel angular pressing, high-pressure torsion, ultrafine grain, electrical conductivity

Nano-particles were doped into YBCO films as pinning centers by a metal organic deposition (MOD) method using trifluoroacetates. Two types of initial solution with a cation ratio of Y: Ba: Cu = 1: 1.5: 3 were prepared; one with the dispersion of SnO2 particles with the size of 15-25 nm and the other one with the dispersion of smaller ZrO2 particles with the size of under 8 nm, then the solution was spin-coated on CeO2/Gd2Zr2O7/Hastelloy substrates. The coated films were calcined at 430 °C in oxygen atmosphere and crystallized at 780 °C in low oxygen atmosphere. From the results of X-ray diffraction analysis (XRD), peaks of BaSnO3 were observed clearly in the YBCO film by the starting solution with SnO2. On the other hands, little peaks corresponding to BaZrO3 were observed in the film by the solution with ZrO2. Many CuO segregations were recognized at the surface of SnO2 doped YBCO film in comparison to the YBCO film with ZrO2 doping. From these results, it is indicated that most of SnO2 particles in precursors are react with Ba during heating. Critical current density ( J C) of the YBCO films by both solutions showed higher performance than that of pure YBCO film in magnetic fields.

We have succeeded in significant improvement in measuring speed of scanning Hall-probe microscopy for two-dimensional characterization of local critical current density in a coated conductor. A typical measuring speed was 36 m/h with a spatial resolution of 1 mm in longitudinal direction and 40 micrometers in width direction while the combination of the speed and the resolution could be changed on demand. This was 200 times faster than the speed of our previous system, and could be applicable to a long-length conductor. From the magnetic field distribution in a remanent state, we could estimate in-plane distribution of local critical current density in nondestructive manner. For example, we could confirm almost homogeneous local properties in a GdBCO coated conductor, and at the same time we detected some defects in the edge of the conductor. Furthermore, we could also confirm the applicability of this method to a multifilamentary coated conductor. These results would be helpful for (1) quality control of an original conductor, (2) that of a finer conductor slit from a wider one, (3) that of a multifilamentary conductor, (4) understanding of macroscopic current transport properties, (5) investigating a typical statistics correlated with the fabrication process, and so on.