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\REBa2\Cu3\Ox (REBCO, RE = rare earth) coated conductors are expected to show high performance for superconducting applications because of their high current density and high mechanical strength. Fujikura has developed REBCO coated conductor over 570 A/cm width at 77 K, self field with over 800 m length. In addition, we have succeeded in developing a 5 T cryocooled REBCO magnet with a stored energy of 426 kJ. The magnet is composed of 24 pancake coils with an inner diameter of 260 mm, and the total length of the REBCO coated conductors is approximately 7.2 km. We confirmed that the REBCO magnet could be excited up to 5 T for 720 min 9 months after the fabrication of the magnet. It is important to validate the long-term operation test results of the REBCO magnets with larger diameters in order to use these conductors in practical superconducting applications. On the other hand, we have fabricated and evaluated a model magnet before we fabricated a 426 kJ cryocooled magnet. The model magnet is composed of 6 REBCO pancake coils and 18 “dummy coils” with an inner diameter of 260 mm and an outer diameter of 515 mm. The model magnet is about the same size and shape as the 426 kJ cryocooled magnet. We have confirmed that the calculated critical current (Ic) of the top pancake coil of the model magnet was in good agreement with the measured coil Ic from 30 to 77 K under the conduction-cooled conditions. In addition, we have evaluated the thermal runaway behavior of the model magnet under the conduction-cooled conditions. As a result, we have confirmed that the model magnet with a 0.3-mm-thick copper stabilizer had sufficient time to ramp down without degradation at 361 A transport current after the detected normal transition. [ABSTRACT FROM PUBLISHER]

Abstract: We have developed an ion-beam-assisted-deposition (IBAD) and a pulsed-laser-deposition (PLD) technique to produce REBa2Cu3O x (RE123, RE: rare earth) coated conductors with high performances. Distributions of critical currents (I c ) in the longitudinal direction were improved in most wires routinely fabricated under optimized process. A typical wire showed I c of 460 A/cm at 77K and self-field, about 200 A/cm at 65K and 3 T and about 300 A/cm at 50K and 5 T. In addition, further high I c values over 800 A/cm were also obtained in thick films. Finally, we succeeded in fabricating an 816.4 m long wire with end-to-end I c of 572 A/cm, corresponding to the new world record I c ×L value of 466,981 Am/cm. [Copyright &y& Elsevier]

The quench characteristics, particularly the normal-zone propagation and increase in hot-spot temperature, of REBa2Cu3Ox (REBCO) coated conductors are important issues for safe operation in the superconducting applications. Although experimental data on the quench characteristics of REBCO coated conductors have been reported only limited data is available specifically on REBCO coated conductors laminated with Cu tape of thickness no less than 0.1 mm, which are expected to be used for high-current operation in future superconducting applications. Here we reported experimental measurements of the normal-zone propagation velocity (NZPV) in REBCO coated conductors laminated with Cu tape of 0.1 mm thickness at 77, 65 and 50 K in a background magnetic field. We also compared these results with the NZPV at 77 K of REBCO coated conductors laminated with Cu stabilizer tape of thickness 0.05 and 0.3 mm. [ABSTRACT FROM AUTHOR]

Dependence of AC transport current losses on bending strains of two kinds of YBCO coated conductors (CCs) manufactured by IBAD/MOCVD and IBAD/PLD processes were investigated. The bending strains were applied to CCs samples by mounting the samples on U-shape sample holders consisted of straight and half-cylindrical sections. The bending strains to the superconductor layer were in tensile and compressive directions. The experimental results showed that the bending dependence of the AC transport current loss could be characterized by the amount of the deteriorations of the conductor critical currents dependent on structure changes of the superconductor layers due to the bending strains, regardless of the CCs manufacturing processes and the directions of the strains. [ABSTRACT FROM AUTHOR]

Abstract: Long length manufacturing approach of YBa2Cu3O7−x (Y-123) conductor was performed using ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD) process in Fujikura Ltd. A new set of reel-to-reel IBAD system was designed using 110cm×15cm assisting ion source. The planer distribution of in-plane texture (Δϕ) for Gd2Zr2O7 template films were studied in large deposition area of 100cm×25cm. The throughput of 5.5m/h with Δϕ of 15° was obtained for Gd2Zr2O7 films grown on 10mm wide tapes. Long Y-123/CeO2/Gd2Zr2O7/Hastelloy tapes were produced by using reel-to-reel vacuum apparatuses of IBAD and PLD. I c of 153A, and 88A were obtained in end-to-end of a 104m long tape, and a 217m long one, respectively. I c of 360A was obtained in a short sample with Y-123 thickness of 2.0μm. A cryo-cooled 5-turn×4-layer small solenoid coil with inner diameter of 60mm was demonstrated using a Y-123 conductor formed by IBAD/PLD method. No severe heat spot was generated even the transporting current exceeded the coil I c value of 355A at 20K. [Copyright &y& Elsevier]

The DRHQ process was applied to the jelly-rolled Nb3 Al precursors having internal Ag stabilizers. The Ag internal stabilizer is effective to improve the superconducting stability of the DRHQ processed conductor with the Ag-stabilizer/non-Ag ratio of 0.32. The DRHQ process needs a reduction of a bending strain of the precursors, such as tape-formed specimen. The maximum Tc and Bc2 (4.2 K) of the DRHQ-processed tape with Ag stabilizer are 18.4 K and 29.7 T, respectively. Large transport core-Jc (4.2 K) of 210 A/mm2 was obtained at high magnetic field of 25 T, which is 20 times larger than that of the typical RHQT-processed wires. On the other hand, Jc in fields below 20 T apparently decreased with increasing the peak heating temperature during the second-RHQ. According to the TEM observation, the stacking faults were still formed in the DRHQ-processed Nb3 Al, but their density becomes very small compared with that of the RHQT-processed Nb3 Al. In addition, the stacking faults gradually vanished with increasing the peak heating temperature. The grain size of several hundred nanometers for the DRHQ-Nb3 Al is still rather small. Thus, these results support that the stacking faults should be dominant as the effective pinning center for the both of RHQT- and DRHQ-processed Nb3 Al conductors. [ABSTRACT FROM AUTHOR]

We tried to enlarge a Nb/Al strand dimension to enhance a current capacity of RHQT-Nb3AI further, So far good fsRHQ operation could be made by using the strand dimension of less than ø 1.35 mm. This time we tried to make RHQ operation by using a Nb/Al rectangular strand of 1.45 × 2.2 mm2 which is double cross-section area of ø 1.35 mm. Bcc phases could he formed even in the large cross-section rectangular strand by RHQ operation. The samples were post-annealed at 800° C for transforming into A15. The resultant Ic and core Jc were 232.5 A and 130 A/mm2 at 4.2 K, 22 T, respectively. These values largely surpassed Ic of 57.5 A and Jc of 72.7 A/mm2 at 4.2 K, 22 T for the sample which was made by using a conventional ø 1.35 mm strand. [ABSTRACT FROM AUTHOR]

We have examined the critical current Ic and n-values of RHQT processed Nb3Al conductors at 4.2 K in a wide range of fields from 14.5 to 25 T in relation to the microstructures obtained. For a point and a tail of Cu-clad rectangular conductor used for a winding, the n-values were determined by fitting the voltage over a taps spacing of 110 or 220 mm to a relationship of V = CIn, in a range from 10-5 to 10-4 V/m. Such n-values were almost the same with each other, indicating the uniformity of a 370 m length of RHQT Nb3Al conductor as the Ic consistency does. The n-value increased monotonously with decreasing a field from 25 T to 18 T, but got saturated to be around 35 at 4.2 K in fields less than 18 T. The n-value at 21 T and 4.2 K, corresponding to 23.5 T and 1.8 K, was about 25, and confirmed to be large enough for NMR uses. [ABSTRACT FROM AUTHOR]

High-field performance of Nb-tube processed Nb/sub 3/Al conductors is improved and allows these conductors for use above 20 T, when continuous direct-heating is applied before final annealing in the fabrication process. In the present study we prepared 0.74 mm/spl phi/ Nb/sub 3/Al wires containing 121/spl times/121 7-core elementary Nb/Al-Mg composites by this modified method and measured their critical current, magnetization and susceptibility as a function of field and temperature. From these measurements, we have found that the volume pinning force, F/sub p/ of these wires simply follows the Kramer's scaling law, i.e. F/sub p//spl prop/B/sub c2//sup 2.5/b/sup 0.5/(1-b)/sup 2/ w here b=B/B/sub c2/, for the entire range of temperature measured, 4.2/spl sim/16 K. Since A15 phase grains formed are very fine, the most probable pinning source seems to be grain boundaries which are dense compared to other possible sources such as interfaces between Nb-Al alloy phase and Nb/sub 3/Al filaments. [ABSTRACT FROM PUBLISHER]

Abstract: We have developed a characterization method for two-dimensional imaging of critical current density in coated conductors (CCs) based on scanning Hall-probe microscopy (SHPM). The distributions of the magnetic field around a sample were measured for several different conditions of external magnetic fields, and then were converted to those of the sheet current density which flowed to shield the external magnetic field or to trap the penetrated magnetic field. As a result, it was found that the amplitude of the sheet current density corresponded to that of critical current density almost in all the area of the sample except for the region where current direction changed. This indicates that we could obtain an in-plane distribution of the critical current density with a spatial resolution of around 100μm in non-destructive manner by this method. We believe that this measurement will be a multifunctional and comprehensive characterization method for coated conductors. [Copyright &y& Elsevier]

Abstract: We have visualized non-uniform current flow in RE123 coated conductors by using a scanning Hall-probe magnetic microscopy (SHPM). Newly developed SHPM system allows us to measure two-dimensional magnetic field distribution with high spatial resolution in micro-meter scale. Corresponding current density distribution can be obtained from the magnetic field image by solving inverted Biot–Savart’s law. One of the most important advantages of the present system is to visualize the current density distribution in practical high transport current and also in wide scanning area. For example, the system has current leads with large capacity up to 500A, and the operating distance can be 15cm by 15cm with a micro-meter step distance. Using the SHPM system, we have successfully visualized current density distributions in the coated conductor, and clarified different kinds of non-uniform current flow. Those insights are very useful to identify local defects as well as non-uniform tape quality. These results indicate that the SHPM system is a powerful diagnostic tool not only to observe spatial inhomogeneities of transport property but also to understand their reason in practical coated conductors. [Copyright &y& Elsevier]

Abstract: This paper describes a process for the fabrication of coated conductor (CC) wires, which is developed by Fujikura, and discusses their properties. These wires are composed of a buffer layer, which is formed by the ion beam assisted deposition (IBAD) technique, and a superconducting layer, which is formed by the pulsed laser deposition (PLD) process. In order to increase the Ic × L which means the product of critical current (Ic ) and the length (L) of the CC wires the Ic value and Ic distribution along the length of CC wires have been improved by using a new PLD pilot plant. The Ic value increases approximately linearly with the thickness of the superconducting layer, and it continues to increase up to a thickness of approximately 4μm or 5μm. The Ic × L value of our fabricated CC wire is 176,023Am. The Ic value of a short sample is 972A/cm. The process rate of IBAD is enhanced up to 100m/h and that of PLD is enhanced up to 20m/h. A 40-m long CC tape, which has an average Ic of 300A, is fabricated by the improved IBAD and PLD techniques. [Copyright &y& Elsevier]

Abstract: We investigated trapped vortices in Y1Ba2Cu3O7−δ (YBCO) coated conductor by using a scanning SQUID microscope (SSM). Several peculiar properties of the vortices were observed such as a large bundle of vortices at a certain position and a coexistence of positive- and negative-sign vortices. Comparing the SSM images with that of low temperature scanning laser microscopy (LTSLM) and SEM, we identified the relationship between local dissipation and position of current blocking defect. Furthermore, regular vortex images were also observed by the SSM in the region where higher J c has been identified by the LTSLM. [Copyright &y& Elsevier]

Abstract: REBCO coated conductors having a performance greater than 300A/cm at 77K have been developed for superconducting applications. The conduction-cooled coils fabricated using REBCO coated conductors are expected to have the high performance because the specific heats of the constituent materials increases greatly with the operating temperature. From the point of view of the coil design using REBCO coated conductors, we must consider the critical current versus the magnetic field characteristics and their temperature dependence. In this study, we fabricated the two-layer stacked racetrack coil whose outer diameter was 92×172mm with 56 turns. The coil used the REBCO coated conductor, whose critical current was around 200A/5mm at 77K self field, manufactured by Fujikura Ltd. We compared with the calculated and measured the voltage distribution of one racetrack coil, which was attached with voltage taps each turn, at 77K in self field. We investigated the Ic of the two-layer coil at 65K and 50K under conduction-cooled conditions. The Ic values of the two-layer coil in self field using a criterion of 10−7 V/cm were achieved 220A at 65K and 386A at 50K, which the central magnetic fields were 0.13T at 65K and 0.23T at 50K, respectively. [Copyright &y& Elsevier]

Abstract: We have developed long RE1Ba2Cu3O7− X (RE123) coated conductors with large current capacity by the ion beam assisted deposition (IBAD) and the pulsed laser deposition using hot wall heating (HW-PLD) technique. As a result, we could fabricate an 8m-long Gd1Ba2Cu3O7− X (Gd123) coated wire with the minimum and maximum critical current (I c) of 951A/cm-w and 1003A/cm-w at 77K, 0T, respectively, measured in 0.7m-long sections by the standard 4-probe technique. Furthermore, we succeeded in preparation of over 600m-long Gd123 coated wire with the uniform I c distribution over 600A/cm-w. It had average, maximum and minimum I c of 665, 698, 609A/cm-w, respectively. The n-values of the sample showed the maximum I c and minimum I c were 40 and 36, respectively. As a result, we set the new world record of I c × L value as 374535Am (= 609A×615m). The in-field performance of this long wire was quite high as well; the minimum I c exceeded 50A/cm-w at 77K, 3T. [Copyright &y& Elsevier]

Abstract: In Fujikura, a large-scale ion-beam-assisted deposition (IBAD) system with a large ion source has been employed to fabricate biaxially textured MgO films. The large-scale IBAD system has multiple deposition lanes where substrate tapes move, and therefore we have to optimize experimental conditions at each lane. We selected an appropriate deposition area and, finally, we successfully fabricated a 1km-length IBAD-MgO film at a production rate of 1km/h. We also studied pulsed-laser-deposited (PLD) CeO2 films directly on the IBAD-MgO films in spite of a large lattice mismatch between CeO2 and MgO. From transmission electron microscope (TEM) observations at an interface between MgO and CeO2 films, it is revealed that there is domain-matching-epitaxy relationship between MgO and CeO2 films. We also fabricated thin (1.0μm) and thick (3.7μm) PLD – GdBa2Cu3O7− x (GdBCO) film on the long-length CeO2/MgO substrate (over 150m). Critical currents (I c) and current density (J c) were over 300 A and 3MA/cm2 respectively for the thin GdBCO film and were about 645 A and 1.7MA/cm2 for the thick GdBCO film at 77K in self-field. [ABSTRACT FROM AUTHOR]

Abstract: The winding technology with high current capacity is one of the important factors in power application of 20MVA/66kV-class superconducting power transformers. High-current power transformer is achieved by transposed conductors made of Rare Earth-based superconducting coated conductors. By transpositions, the improvement of uniformity of strand current distribution makes it possible to reduce the total number of strands and AC loss of coils. In this study, the high-T c superconducting coil was made by transposed 24 strands of 5mm-wide Rare Earth-based superconducting coated conductors and operated at a current of 1kA. The test results of AC and DC current characteristics and AC loss are reported. [Copyright &y& Elsevier]

Abstract: For practical applications of high-temperature superconductor tape, the high production rate of tapes is needed to reduce its cost. Recently, the long-length coated conductor with high performance has been fabricated by an ion beam assisted deposition/pulsed laser deposition (IBAD/PLD) method in Fujikura. In IBAD process, we adopted IBAD–Gd2Zr2O7 (GZO) film. The process speed of IBAD–GZO film was increased up to 5m/h using a polished metal substrate tape. To fabricate biaxially-textured buffer layers at a higher rate, we have started to develop another structures such as (a) IBAD–GZO/IBAD–MgO (3-fold symmetry) and (b) IBAD–MgO (4-fold symmetry). In the case (a), we fabricated GdBCO/CeO2/IBAD–GZO/IBAD–MgO tape and the critical current was Ic =550A/cm (2.46MA/cm2) and throughput of IBAD processes were 20m/h. In the case (b), IBAD–MgO short samples with ΔΦ of 9°–11° were obtained at 500m/h. The 500m/h (10mm width) is extremely high rate in IBAD process in the world. As long-length IBAD layer 10m, 50m and 100m IBAD–MgO films were fabricated at the speed of 100m/h. After CeO2 deposition, in-plane textures of these samples were ΔΦ of 3.7°–3.7°, 4.1°–4.9° and 4.2°–4.8°. Using some of these buffer layers, we have obtained GdBCO film with Ic =400A/cm (2MA/cm2, 10m) and Ic =550A/cm (2.7MA/cm2, short sample). [Copyright &y& Elsevier]