Search

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.

We are developing an elemental technology for 66 kV/6.9 kV 20 MVA-class power transformer with YBCO conductors. The protection of short-circuit technology is one of the elemental technologies for HTS transformer. Since short-circuit current is much higher than critical current of YBCO tape, there is a possibility that superconducting characteristics may be damaged during short-circuit period. We made a conductor to compose the YBCO tape with copper tape. We manufactured 6.9 kV/2.3 kV 400 kVA-class YBCO model transformer using this conductor and performed short-circuit current test. The short-circuit current of primary winding was 346 A which was about six times larger than the rated current. The I–V characteristics of the winding did not change before and after the test. We may consider this conductor withstands short-circuit current.

We are developing elemental technology for 66 kV/6.9 kV 20 MVA-class YBCO power transformer. The YBCO transformer is considered to have a possibility to stabilize the power system by improving function of fault current limiting. Current limiting behavior functions over critical current flows. There is a possibility that superconducting characteristic may be damaged due to increase in temperature of YBCO tapes. Therefore, we have taken a measure to combine YBCO tape with CuNi tape or Cu Tape. We manufactured model coils using these conductors and conducted the AC over-current tests. The test current was two to seven times larger than the I c of conductor and it was damped with time from its maximum value according to the generation of conductor resistance. We verified the effectiveness of current limiting characteristics. In these tests, the I c of model coil did not degrade. We consider this conductor to be able to withstand AC over-current with the function of current limiting.

In the last few years, REBCO coated conductors having a performance greater than a few hundred amperes per cm at 77 K have been developed for superconducting applications. Coils that use REBCO coated conductors are expected to have the high operating current ( I op ) against the critical current ( I c ) of the coil. In this paper we report the experimental results of a small cryocooled racetrack magnet (70 × 150 mm in inner diameter, 100 × 180 mm in outer diameter, 27 mm in height, 50 m (12.5 m × 4 coils) in total length) fabricated using a REBCO coated conductor, formed by IBAD/PLD method. We measured the critical current of the magnet from 50 K to 20 K under cryocooled conditions. The critical current was found to be 450 A at 20 K. The magnetic field of 0.54 T was generated at the center of the magnet. We also investigated the stability of the racetrack magnet, at the current of 382.5 A, and I op / I c ratio of approximately 85%, for 1 h at 20 K.

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 100 μm in non-destructive manner by this method. We believe that this measurement will be a multifunctional and comprehensive characterization method for coated conductors.

The spatial homogeneity of PLD GdBCO coated conductors with high critical current of 620 A/cm-w was studied. By using laser-induced thermoelectric-imaging and low-temperature laser scanning microscopy we investigate film structure homogeneity, Tc and Jc variation. Our results imply that critical temperature variation along the sample of less than 0.2 K and Ic variation is fairly small. Our spatially resolved measurements reveal good in-plane homogeneity and current carrying capability. This shows a potential to use such conductors in various types of applications even with striated multi-filamentary conductors in which long-length narrow strips are required for AC-loss reduction.

A single-phase 10 kVA transformer was designed and fabricated with RE1Ba2Cu30O7-δ (REBCO, RE: Rare Earth) superconducting tapes to quantitatively investigate the transition phenomenon of REBCO superconducting tapes to normal state due to a fault excess current. The voltage ratio was 1:1 and the rated voltage was 393 V. It had four windings. The primary and secondary windings had auxiliary windings in addition to main ones respectively. The main and auxiliary windings were connected in parallel in the both sides. The addition of the auxiliary windings made it possible to observe the induced normal resistances in the respective main ones individually. First usual performance tests were carried out and a stable operation as designed was confirmed. In steady state almost all of the current flowed in the main windings due to the small leakage reactance between them. At a sudden short-circuit test, the main windings quenched due to excess current over the critical current and the current was reduced to one fortieth as compared with the case of no current limiting function. It was clarified the whole of the main windings did not shift to normal state though the current exceeded the critical current all over the length and the induced normal zone was almost proportional to the primary voltage.

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.

We have investigated critical current Ic properties of 600 A/cm-class GdBa2Cu3O7-δ (GdBCO) coated conductor (CC) deposited on IBAD template. 2.5 μm thick GdBCO layer has been obtained by pulse laser deposition without degradation of critical current density by an improved heating condition in reel-to-reel deposition process. This enables stable production of long length CC with Ic (77 K, self-field) of 600 A/cm-w. In-filed Ic has also shown high value e.g., Ic@77 K, 3 T=33 A/cm-w, Ic@20 K, 27 T=107 A/cm-w. These experimental results obtained in a wide range of bias conditions of temperature T, magnetic field B and field angle θ are useful as a fundamental data for design of superconducting devices such as coil winding and magnet. Furthermore, we have also shown that our proposed analytical expression of electric field vs. current density (E-J) characteristics agrees well with the experimental results. This analytical expression allows us to predictIc-B-T property as well as E-J characteristics at arbitrary conditions of B and T.

We have studied a hot-wall heating system to produce GdBa 2 Cu 3 O y (GdBCO) films with large critical currents ( I c ) at a high production rate by a pulsed-laser-deposition (PLD) method. GdBCO films fabricated at a production rate of 30 m/h under the optimized conditions, especially a distance of 95 mm between the target and the substrate (T–S), exhibited high critical current densities ( J c ) of about 3 MA/cm 2 and I c over 300 A at a thickness of 1–2 μm. Furthermore, long GdBCO tapes prepared by repeated depositions at each tape-passing speed of 80 m/h showed uniform I c distribution along the longitudinal direction, because the hot-wall system enabled to stabilize temperature within a few degrees at 800 °C. A 170 m long tape with I c over 600 A was successfully fabricated at a production rate of 16 m/h using a laser power of 360 W.

In Japan we started a national project to develop a 66/6.9 kV–20 MVA transformer with REBCO superconducting tapes in 2006. This paper gives an overview of progress of the development of superconducting transformers in Japan and also describes the fundamental technologies studied before now to realize a 66/6.9 kV–20 MVA transformer as follows. To reduce the ac loss in REBCO superconducting thin tapes, authors proposed a new method different from the conventional technique of reducing the ac loss in superconducting multifilamentary wires. It consists of scribing process into a multifilamentary structure by laser or chemical etching, and a special winding process. Making a multilayered solenoidal coil with laser-scribed REBCO tapes, we verified the ac loss reduction in proportion to a filament width even in coil configuration. In addition, to realize a current capacity more than the rated secondary current of 2.4 kA, we first investigated the workability of REBCO tapes in the actual winding process with forming a transposed parallel conductor, where REBCO tapes were bent edgewise at transposing points. Making a test coil of a 24-strand parallel conductor, we verified no degradation of the critical current and nearly uniform current distribution among the tapes. The result suggests the applicability of the method of enhancing the current capacity by forming a parallel conductor with REBCO tapes. Further, to realize the dielectric strength regulated for the Japanese standards, i.e. lightning impulse withstand level of 350 kV and excess ac voltage of 140 kV, we made test coils and carried out dielectric breakdown tests. As a result, we got hold of the required insulation distance at the important points from the viewpoint of insulation design.

We have studied two types of heating systems to produce thick GdBa2Cu3O7−X (Gd123) films with high critical current (Ic) stably at a high speed by the PLD method. Material yields of both PLD systems reached about 50–60% by optimization of evaporation condition. Hot-wall heating type (type 2) could fabricate the thicker Gd123 film with the higher Ic compared to contact heating type (type 1) and maximum Ic reached 1040 A at about 6 μm thick. Furthermore, it was estimated that type 2 could fabricate Gd123 film with an Ic of about 700 A at about twice speed compared to type 1. Finally, it was considered that the hot-wall heating type was very advantageous to prepare thick Gd123 film with high Ic at a high speed from the system structure.

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 500 A, and the operating distance can be 15 cm by 15 cm 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.

As one of the programs in the Ministry of Economy, Trade and Industry (METI) project regarding R&D on superconducting coated conductor, three-phase superconducting fault current limiter (SFCL) for 6.6 kV application was developed and successfully tested. The developed SFCL was mainly comprised three-phase set of current limiting coils installed in a sub-cooled nitrogen cryostat with a GM cryocooler, circuit breakers and a sequence circuit. The whole system was installed in a cubicle. Two tapes of coated conductor were wound in parallel in each coil to obtain the rated current of 72 A rms. After developing the whole SFCL system, short circuit experiments were implemented with a short circuit generator. In a three-line ground fault test, the SFCL successfully restricted the prospected short circuit current over 1.6 kA to about 800 A by the applied voltage of 6.6 kV. The SFCL was installed in a user field and connected with a gas engine generator, followed by a consecutive operation. In this program, 600 A class FCL coil, with which four coated conductor tapes were wound, was also developed. The coil showed sufficiently low AC loss at the rated current. With these results, the program attained the planned target of the fundamentals for the 6.6 kV/600 A SFCL.

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 I c × L which means the product of critical current ( I c ) and the length ( L ) of the CC wires the I c value and I c distribution along the length of CC wires have been improved by using a new PLD pilot plant. The I c value increases approximately linearly with the thickness of the superconducting layer, and it continues to increase up to a thickness of approximately 4 μm or 5 μm. The I c × L value of our fabricated CC wire is 176,023 Am. The I c value of a short sample is 972 A/cm. The process rate of IBAD is enhanced up to 100 m/h and that of PLD is enhanced up to 20 m/h. A 40-m long CC tape, which has an average I c of 300 A, is fabricated by the improved IBAD and PLD techniques.

We designed and fabricated a 7.5 kW-360 rpm synchronous motor with a superconducting rotor. The rotor was 6-pole type and has no iron core. The armature winding was wound with copper wires. 6 pieces of racetrack-shaped field coils were wound with 5 mm wide RE1Ba2Cu3O7-delta (REBCO, RE:Rare Earth) superconducting tapes produced by an ion beam assisted deposition method and a pulsed laser deposition method. The total length of REBCO tape was 400 m per a field coil. We confirmed the good transport properties of the respective field coils up to 80 A at 40 to 50 K before and also after the assembly to a motor. The maximum magnetic field in the field coils was 0.67 T. The superconducting rotor was cooled down to around 40 K by forced-flowed helium gas and the completed motor was tested in a similar way to conventional motors. As a result of a load test, the designed operation of 7.5 kW at 360 rpm was verified for the rated field current of 60 A. Even when the field current was increased up to 70 A at 40 K, the temperature at each part of the superconducting rotor was held constant and the quite stable operation up to 11 kW at 360 rpm was also achieved.

We have carried out observations of current flow in processed RE123 coated conductors using a scanning Hall-probe microscope. Using this system, the position of defects and the resulting disturbed current flow could be observed. The two-dimensional current distribution in a 10-filament formed coated conductor (400 mum width and 100 mum space) was also investigated. Current sharing and the current distribution in each filament were quantitatively estimated. Furthermore, current penetration in quasi-static AC current mode was also measured.

As one of the programs in the Ministry of Economy, Trade and Industry (METI) R&D project on coated conductors, we developed a three-phase 6.6 kV superconducting fault current limiter (SFCL) and conducted some evaluation tests. The developed SFCL mainly comprised a set of three-phase current-limiting coils installed in a sub-cooled nitrogen cryostat with a Gifford-McMahon (GM) cryocooler, circuit breakers, and a sequence control circuit. Two tapes were wound in parallel in each limiting coil to obtain a rated current of 72 A rms. AC characteristics of each coil were measured, and relevant performance metrics were obtained. The whole system was installed in a cubicle. Short circuit experiments were then conducted with a short circuit generator. In a three-line ground fault test, the SFCL successfully restricted a short circuit current of over 1.56 kA to about 840 A with an applied voltage of 6.6 kV. The system integration ability and the obtained data show the promise of this approach for practical implementation. The SFCL was ready for user field tests.

By an IBAD/PLD method, a 500 m-length high-performance GdBa2Cu3Ox (GdBCO) coated conductor with BaZrO3 (BZO) was fabricated. End-to-end Ic of the 503.5 m tape was 349.6 A/cm at 77 K, corresponding Ic times L value of 176,023 Am. New approaches to decrease the thickness of IBAD buffer layers were developed by combination of IBAD-MgO(111) and IBAD-Gd2Zr2O7 (GZO). The maximum Jc of the GdBCO on the buffer layer was 550 A/cm. We also started to investigate IBAD-MgO(OOl) by using a large IBAD system with a 110 cm times 15 cm ion source. A 50 m-length IBAD-MgO tape with DeltaPhi of 13deg was fabricated at a 100 m/h-1 pass. Insulated REBCO wires with Cu or Ni-Cr lamination were developed using 5 mm-wide conductors sliced from 10 mm-wide IBAD/PLD tapes. Practical long insulated wires were supplied for several prototypes of motors, transformers and fault current limiters in fiscal 2007.

We have developed long Gd-123 coated conductors by ion-beam-assisted deposition (IBAD) and pulsed-laser-deposition (PLD) method. Recently, large-scale reel-to-reel apparatus with the 110 cm × 15 cm assisting ion source was introduced to IBAD system. It was enable to produce 500 m-class IBAD–Gd 2 Zr 2 O 7 (GZO) tapes with Δ ϕ of below 15° and high throughputs of 3 m/h. Furthermore, apparatus with multi-lane and laser scanning was introduced to PLD system. As a result, end to end I c of 318 A were obtained for a 201.5 m long tape, and I c × L values were 64,077 Am. Furthermore, 500 m-class deposition was carried out by improving PLD conditions. As a result, I c × L values of 112,166 Am was obtained and it’s a world record on August 2007. In the short samples, I c of over 500 A was obtained with Gd-123 thickness of 2.0 μm and over 100 A was obtained in magnetic field of 3 T, perpendicular to c -axis.

One of the programs in the Ministry of Economy and Trade and Industry (METI) project regarding R & D on YBCO conductor is to evaluate the applicability of the developed conductor toward several applications. This paper focuses on a fault current limiter (FCL) as one of the expected power applications. YBCO tape conductors with ion beam assisted deposition (IBAD) substrate are used in this work. In order to obtain high resistance of the conductor, which is preferable to an FCL, the thickness of the protecting layer made of silver was decreased as possible. Then high-resistive metal stabilizing layer is attached on the silver layer to improve stability. Obtaining the relevant current limiting performance on short sample experiments, model coils were developed to aim the 6.6 kV-class FCL. Short circuit experiments were implemented with a short circuit generator. The coil successfully restricted the short circuit current over 17 kA to about 700 A by the applied voltage of 3.8 kV, which is nominal phase-to-ground voltage. The experimental results show good agreement with computer analyses and show promising toward the application.

We are developing a 7.5 kW-360 rpm synchronous motor with a superconducting rotor. The rotor is 6-pole type and has no iron core. The armature winding is wound with copper. The designed operating temperature is 40 K. It will be cooled by forced-flowed helium gas. We have finished the winding of the first superconducting field coil with YBCO superconducting tapes fabricated by IBAD-PLD method. It is a 62-layer solenoidal coil. The total length of YBCO tape is 400 m. The magnetic field in the field winding is about 0.4 T at maximum and that in the gap is 0.2 T. We cooled it down to 20 K by G-M type cryocooler and investigate the transport properties in advance of the winding of the other field coils. We verified the stable operation up to 100 A at 40 K against the rated current of 50 A. In addition we prepared the cryogenic rotor system and installed 6 pieces of dummy copper coils instead of superconducting coils. We cooled it down to 30 K by forced-flowing helium gas and tested it by rotating up to 360 rpm. We verified the satisfactory good mechanical and thermal operation.

We have developed a long Y-123 coated conductors by ion-beam-assisted deposition (IBAD) and pulsed-laser-deposition (PLD) method. Now, we can routinely obtained 100 m class Y-123 tapes with over 100 A at 77 K. For power applications using Y-123 conductors, coiling and cooling techniques are important elements. From 2004, we have developed and demonstrated a solenoid type coil that is the most suitable for practical application because it has advantage such as (1) uniformity of magnetic field (2) no joint. In this paper, we describe the development of conduction-cooled HTS test coil that has 14 turn × 22 layers using 100 m Y-123 conductors. In order to use the conduction cooling system, the Y-123 conductors were stabilized for 0.1 mm thick Cu tapes and spacers between the layers consisted of aluminum nitride in the coils. In the demonstration of this coil at 30 K, 40 K, 50 K, 60 K and 77 K by cryo-cooling system, the good cooling and superconducting performances were observed. The central magnetic fields of over 1 T were successfully obtained with operating currents of over 400 A and under 40 K. Furthermore, this coil was operated on additional magnetic fields of 3 T by combination of LTS magnets. The central magnetic fields of 0.5 T were generated from the cooled HTS coils with operating current of 190 A on additional magnetic fields of 3 T by LTS magnets at 30 K. Total magnetic fields were exceeded 3.5 T at 30 K.

Four 5 mm-wide YBCO conductors with identical critical current were assembled face to face to obtain a stacked YBCO conductor. The magnetization losses without transport current, the transport losses without external magnetic field, and the total AC losses of the stacked YBCO conductor as well as a single YBCO conductor carrying various transport currents in transverse magnetic fields with various orientations were measured. The difference between the AC loss characteristics of the stacked YBCO conductor and those of the single YBCO conductor was clarified.

We developed a 15 kW synchronous motor with a fixed superconducting field winding. It was 8-pole type. Each field coil was a racetrack-shaped single pancake wound with a YBCO superconducting tape. It was fabricated by IBAD-PLD method and 10 mm in width. The rotating armature was composed of a copper winding and an iron core. The field coils were conduction-cooled down to 20 to 30 K through a copper pipe attached to the copper coil flange, in which helium gas was forced-flowed. The completed motor was first tested in the Suzuka factory of Japan motor and Generator Co. Ltd. before shipping as usual. Then it was moved to the test site of the Nagasaki shipyard of Mitsubishi Heavy Industry Ltd. and installed into a ship propulsion test system, which had a propeller with a diameter of 0.5 m. We verified the quite stable underwater operation and the output power of 15 kW-360 rpm as designed.

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 IBAD/PLD and IBAD/ 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.

Temperature dependence of the ac loss in YBCO superconducting tapes fabricated by IBAD-PLD technique was investigated. The ac loss was measured with a saddle-shaped pickup coil by applying magnetic field perpendicular to the tape. Temperature dependence of Ic-B characteristics was estimated from the observed magnetization curves. The Ic-B curves normalized by the zero-field Ic at the respective temperature coincided with one master curve regardless of temperature. Ic-B characteristics of YBCO superconducting tapes are scaled with temperature. According, when the magnetization curves and the ac loss vs field amplitude curves are normalized by using the zero field Ic at the respective temperature, they coincided with one master curve for any temperature from 4.2 to 77 K. It is verified that the magnetization and the ac loss are scaled with temperature.

Three YBCO coated conductors with various critical currents, up to 189 A, were prepared. The magnetization losses without transport current and the total AC losses of the conductors carrying various transport currents in transverse magnetic fields with various orientations were measured electromagnetically to study the AC loss characteristics systematically. The measured total AC losses were compared with the numerical values using a one-dimensional FEM model

We experimentally investigated dependence of AC transport current loss characteristics of HoBCO on bending strains. The losses were compared with the losses in the straight conductors. The measurement results showed that values of the AC losses were affected by the bending strains. However, when the losses and the amplitudes of the transport currents were normalized by the strain dependent critical current, curves of the losses vs. the amplitude of the currents fell into one curve unless superconducting layers of the conductors get damages caused by bending strains. Based on these results, it can be considered that the AC transport current loss characteristics of HoBCO subjected to bending strain can be estimated by knowing values of critical currents of bent conductors and the loss characteristics of straight ones in the range where the bending strains do not damage the superconductor layers

Thick YBa2Cu3O7-x (YBCO) films with high critical current density (Jc) values were deposited by pulsed-laser deposition (PLD) on Hastelloy with a textured CeO2/Gd2Zr2O7 buffer layer. Both cross-sectional and plan-view TEM specimens of the YBCO films were prepared, and then the nanostructural characterization of the films was performed by transmission electron microscopy (TEM). The YBCO films less than 1 μm thick were predominantly composed of c-axis-oriented grains, however, many a-axis-oriented grains, which grew larger with the increase of the thickness of the YBCO film, were formed beyond about 1 μm from the CeO2 interface. We found Y2O3 and copper oxides between a- and c-axes-oriented grains. In particular, Y2O3 grains were formed between the {001} plane of an a-axis-oriented grain and the {100} or {010} plane of a c-axis-oriented grain. The orientation relationships between Y2O3 and YBCO are found to be; (001)YBCO//(001)Y2O3 and (100)YBCO//(110)Y2O3. In addition, we also found gaps between YBCO grains. Since a-axis-oriented grain growth and the formation of Y2O3, copper oxides and the gaps are considered to reduce the J c values of the YBCO film, it is important to determine the optimum process conditions to suppress the nucleation of a-axis-oriented grains, impurity oxides and gaps.

The texture evolution property of Gd 2 Zr 2 O 7 (GZO) template films on non-textured Ni-based alloy was studied by off-normal ion-beam-assisted deposition (IBAD) at low temperature of 200 °C, with varied bombarding ion elements of Ar, Ne, and O. In all cases a 〈1 1 1〉 axis aligned toward the ion incident direction preserving out-of-plane (1 0 0) alignment. The in-plane mosaic spread (Δ ϕ ) were clearly deteriorated for GZO films formed with assisting ions of Ar + Ne mixture or pure oxygen, compared to the case for pure Ar ion assisting. On the other hand, no recognizable ion elemental dependence on Δ ϕ was observed when GZO films were homoepitaxially grown by IBAD on already textured GZO surface.

Three types of YBCO films were deposited on metal tapes with biaxially textured CeO 2 /Gd 2 Zr 2 O 7 multilayer. One YBCO film 4 μm in thickness was formed by pulsed-laser deposition (PLD) on the stationary substrate and another film 3 μm in thickness by PLD using a reel-to-reel substrate tape transferring system. I c values of the films were 173 A and 293 A, respectively A further film 1 μm in thickness was fabricated by multiple-stage chemical vapor deposition (MSCVD). The I c value of the MSCVD-YBCO film was 100 A. The microstructures of these YBCO films were characterized using transmission electron microscopy (TEM). In the PLD-YBCO films, the films less than 1 μm thick were predominantly composed of c -axis oriented grains which were considered to grow spirally, however, irregular instances of a -axis oriented grains were also found. The a -axis oriented grains size increased with increasing thickness of the YBCO films. In the 4 μm-thick PLD-YBCO film with an I c value of 173 A, a -axis oriented grains were considered to nucleate on the CeO 2 . We found many Y 2 O 3 and cupper oxides at the boundaries between a - and c -axes oriented grains and the orientation relationships between YBCO and Y 2 O 3 were determined to be as follows: (0 0 1)YBCO//(0 0 1)Y 2 O 3 and (1 0 0)YBCO//(1 1 0)Y 2 O 3 . We also found many gaps and pores between YBCO grains. Nucleation of a -axis oriented grains was completely suppressed on the CeO 2 in the 3 μm-thick PLD-YBCO film with an I c value of 293 A. In the MSCVD-YBCO film, the YBCO film mostly consisted of c -axis oriented grains, however a -axis oriented grains and polycrystal also formed in the film. As the MSCVD-YBCO film became thicker, the a -axis oriented grains grew large, as same as in the PLD-YBCO films. The growth rate of a -axis oriented grain along the substrate normal was much higher than that of c -axis oriented grains in comparison to the difference in the growth rate between a - and c -axes oriented grains in the PLD-YBCO. In these specimens, the grain growth of the a -axis oriented grains was considered to be one of the most significant causes of degradation of J c values in the YBCO films.

We investigated the ac loss properties of a YBCO superconducting tape fabricated by TFA-MOD technique. The thickness of the YBCO layer is 1.2 μm. A 6-tape stack of 50 mm in length and 10 mm in width was inserted into a saddle-shaped pickup coil. The ac loss was measured at 35–77 K by applying an external ac magnetic field. The magnetic field angle was changed by rotating the sample stack around its longitudinal axis. The effective penetration field, which corresponds to the breaking point of an ac loss curve, decreased with increasing field angle though it was much smaller than that which was estimated for a superconducting slab with the same thickness as the width of a tape. As a result, the ac loss increased monotonically with an increasing field angle against the wide surface for any amplitude. The observed field angular dependence of the ac loss agreed with the theoretically predicted one by using the observed ac losses in perpendicular magnetic field. Anyway the ac loss for a larger amplitude than the effective penetration field was proportional to the critical current density and the projective width of a tape in the direction of the applied magnetic field for any field angle and any temperature as well known. In addition we estimated the magnetic field, B , dependence of the critical current, I c , from the observed magnetization curves. It was shown that zero-field I c appeared to be a linear function of temperature and I c – B characteristics was scaled with zero-field I c . We also discussed a difference in I c – B characteristics and its temperature dependence between TFA-MOD tapes and IBAD-PLD ones.

We investigated the dependence of critical current, Ic, of YBCO tapes on the mechanical bending strain in order to apply them to solenoid and pancake type magnets. The tensile and compressive bending strains were applied to the YBCO tapes. The thickness of the YBCO layer on the CeO2 and Y2O3 buffer layers was 0.5 and 1.0 μm, respectively. The Ag cap layer has thickness of 10, 20, and 30 μm respectively. In every sample, no degradation of the normalized critical current, Ic/Ic0, was observed up to the first tensile and compressive strains of approximately 0.4% and 0.5%, respectively. The strain property of the YBCO tapes that were deposited with the 20 and 30 μm thick Ag cap layers showed an improvement over the tape that was deposited with the 10 μm thick Ag cap layer in terms of the tensile and compressive strains of approximately 0.5% and 0.6%, respectively. Cracks were observed on the YBCO film surface under a tensile bending strain of over 0.5%. The generation of the crack appears to be the primary reason for the Ic/Ic0 degradation. The heat cycle test was performed 10 times by applying the tensile strains of approximately 0%, 0.3% and 0.5%. The degradation of Ic/Ic0 was not observed in every sample.

Long YBa2Cu3Ox (Y-123) coated tapes were produced by reel-to-reel continuous processes using Ion-Beam-Assisted Deposition (IBAD) and Pulsed-Laser-Deposition (PLD). Biaxially textured Gd2Zr2O7 buffer layers up to 255 m long were fabricated by IBAD with the production speed of 0.5–1.0 m/h. Y-123 films were formed on them by PLD with the tape speed of 1.0–4.0 m/h. A 105 m long Y-123 film was formed with the uniform thickness of 1.0 μm and the Δϕ of 3–4°. The end-to-end Ic of 126 A was achieved at 77 K, 0 T, whose I–V curve had the n-value of 28.5. The Ic times length reached 13,230 A. Another 70 m long Y-123 tape with the Ic of over 90 A (77 K, 0 T) was wound into a solenoid type magnet whose inner diameter was 60 mm. The central magnetic field of 0.082 T was obtained at 77 K, with operating current of 42 A and that of 0.27 T was obtained at 66 K, with operating current of 130 A.

We investigated the ac loss properties of YBCO superconducting tapes fabricated by IBAD-PLD technique. The thickness of a YBCO superconducting layer was 0.5 and 1 /spl mu/m. Sample tapes of 60 mm in length and 10 mm in width were stacked into multilayers and inserted into a saddle-shaped pickup coil. The ac loss was measured at 64 K and 77 K by applying external ac magnetic field. The magnetic field angle was changed by rotating the sample stack around its longitudinal axis. The ac loss for the smaller amplitude than the effective penetration field strongly depended on the number of stacked tapes owing to the demagnetization effect. On the other hand, the ac loss for the much larger amplitude than that was independent of the number of tapes. In addition the ac loss decreased monotonically with decreasing field angle against the wide surface for any amplitude. We proposed the theoretical expression to estimate the ac losses for any field angle by using the observed ac losses in perpendicular magnetic field and confirmed the applicability by good agreement between theory and experiment.

Current transport characteristics in a Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) coated conductor fabricated by a trifluoroacetates-metal organic deposition (TFA-MOD) process were investigated over a wide range of temperature and magnetic field up to 25 T. Improved TFA-MOD process was successfully introduced for the better property of critical current density, J/sub c/, at high magnetic fields. The J/sub c/ and critical current, I/sub c/, values of multi-coated film with 1.2 /spl mu/m thickness and 1 cm width were 2.1 MA/cm/sup 2/ and 251 A at 77 K in self-field. Additionally, the superior J/sub c/ properties remained even at high magnetic fields over 20 T and lower temperature, e.g. J/sub c/ value at 30 K in 25 T was 1.0 MA/cm/sup 2/. The J/sub c/ value was about 2.5 times higher than those of previous TFA-MOD process at wide range of magnetic field. Moreover, the statistical distribution of J/sub c/ in the conductor was also estimated within a framework of the percolation model. The uniformity in the YBCO coated conductor was improved by optimizing the TFA-MOD process.

Long length Y-123 superconducting tapes were produced by reel-to-reel continuous vacuum processing, by using Ion-Beam-Assisted Deposition (IBAD) and Pulsed-Laser-Deposition (PLD). Biaxially textured Gd/sub 2/Zr/sub 2/O/sub 7/ buffer layers up to 255-m long were fabricated by IBAD with production speed of 0.5-1.0 m/h. Y-123 films were formed on them by PLD with production speed of 1.0-4.0 m/h. A 105-m long Y-123 film was fabricated with uniform thickness of 1.0 /spl mu/m and /spl Delta//spl phi/ of 3-4/spl deg/. I/sub c/ of 126 A was obtained in end-to-end at 77 K, 0 T, whose I-V curve had n-value of 28.5. I/sub c/ times length reached 13,230 Am. Another 70-m long Y-123 tape with I/sub c/ over 90 A (77 K, 0 T) was wound into a Solenoid type magnet whose inner diameter was 60 mm. The central field of 0.27 T was obtained at 66 K, with operating current of 130 A.

The AC losses of YBCO coated conductors fabricated by the IBAD/PLD method were electromagnetically measured. Both the magnetization loss without transport current and the total AC loss during the simultaneous application of AC transport current and an AC external magnetic field were measured. The AC losses were numerically calculated using the one-dimensional FEM model. The magnetic field dependence and the spatial distribution of critical current density were taken into account in numerical calculations, and the calculated AC losses were compared with the measured AC losses. The critical current, the transport current, and the applied external magnetic field were varied in order to calculate the total AC loss systematically.

Spatially resolved measurements of dissipative state in YBCO coated conductors have been carried out by use of the low temperature scanning laser microscopy (LTSLM). It has been shown that the current dependent dissipation peak is well scaled by the Gaussian distribution, and its normalized distribution becomes narrower in inversely proportion to the square root of power index in the local current-voltage characteristic. From the LTSLM analysis, we can collect positional information of current limiting coordinate as well as spatial variation of local critical current. Optimizing the measurement condition, we also succeeded to visualize the dissipation even in the tape which is covered by a 10 /spl mu/m thick Ag stabilization layer.

Although the metalorganic deposition (MOD) process using metal trifuluoroacetete (TFA) is considered to be a strong candidate due to its low cost and high J c performance as a fabrication process for coated conductors of YBa 2 Cu 3 O 7 − x (YBCO), the long calcination time of 10 h for 300 nm YBCO thickness was a problem that needed to be solved in the case of the MOD process using the TFA salts for all elements (all TFA solution). In this study, in order to shorten the calcination time, a new combination of starting materials was developed. Through the investigation of the generation rate of hydro fluoride (HF) gas during calcination, it was found that the high generation rate at a high heating rate is the reason for the bubbling which prevents an increase of the heating rate. Therefore, the amount of fluorine (F) in the starting material was reduced by using the Cu-salt without F while maintaining the basic crystallization reaction in this process. A new heating process using these materials has been developed. Consequently, the calcination time was shortened to 40% using the All TFA solution and an overall transport I c value of 292 A for 1 cm width was obtained (77 K in self-field).

As a method of the fabrication process of YBa 2 Cu 3 O 7− x (YBCO) coated conductors, the metalorganic deposition (MOD) process using metal trifluoroacetates (TFA) has been considered to be a strong candidate as a low cost fabrication process for coated conductors with high J c . In the case of the MOD process using the TFA salts for the all three elements, it requires several tens hours in the calcination process for each single coated film to minimize the generation of pores in the film. In order to shorten the calcination time, a new combination of starting materials was developed. In this study, the new heating process for these new materials has been investigated. Consequently, the calcination time was shortened to be about 17%. Also, the overall transport I c of 292 A and the J c value of 2.0 MA/cm 2 were achieved with 1.48 μm in thickness at 77 K in self-field.

100-m class Y-123 coated conductors were demonstrated by using reel-to-reel vacuum apparatuses of ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD). The window for Gd 2 Zr 2 O 7 deposition condition was quite wide and 100-m long IBAD-Gd 2 Zr 2 O 7 template films were routinely obtained with ΔΦ of 10° on non-textured Ni-alloy tapes. 100-m long second buffer layers of Y 2 O 3 or CeO 2 were grown by PLD on the IBAD templates with ΔΦ of 7-8°, or 5-6°, respectively. Y-123 films with ΔΦ of 7° were formed on the substrate of Y 2 O 3 //IBAD-Gd 2 Zr 2 O 7 // Hastelloy by PLD. End-to-end I c of 38 A and J c of 0.76 MA/cm 2 (77 K, self-field) were obtained in a 100-m long sample. On the other hand, ΔΦ of 3° was obtained on the substrate of CeO 2 //IBAD-Gd 2 Zr 2 O 7 //Hastelloy. J c of 2.9 MA/cm 2 were obtained in a 0.1-m long Y-123 film, and J c was improved to 1.6 MA/cm 2 for an 80-m long Y-123 tape.

The E – J characteristics were measured for a YBCO coated-conductor by using AC inductive method of third-harmonic voltage. The results are compared with the measurements obtained by the four probe method and DC relaxation method of magnetization. The results by three kinds of measurements meet approximately on a single curve and E – J curve in a wide range of electric field is obtained. Hence, the third-harmonic voltage method is useful for a continuous measurement of J c property of long coated tape. The obtained E – J characteristics are argued.

We investigated the ac loss properties of a YBCO superconducting tape fabricated by IBAD–PLD technique. The YBCO layer is 0.5 μm thick. We measured the ac losses by a pickup coil method at 77 and 64 K using 3- and 6-tape stacks in addition to a single tape, where the tapes were arranged in the vertical direction to the wide surface. Sample tapes with a length of 60 mm were inserted into a saddle-shaped pickup coil and rotated around the central axis. The ac loss for the larger amplitude than the effective penetration field into the center of a tape was independent of the number of stacked tapes and proportional to the projective width in the direction of applied magnetic field. On the other hand, the ac loss for the small amplitude depended strongly on the number of stacked tapes due to the demagnetization effect. In addition we estimated the magnetic field dependence of the critical current density from the observed magnetization curves and also discussed on the origin of the anisotropy in ac loss property.

The recent progress in R&D of coated conductors by TFA–MOD process was reviewed. For the several targets, such as high superconducting performance, high production rate, long tape etc., the steady progresses could be recognized. The high J c and I c values of 3.6 MA/cm 2 and 291 A were achieved by using a highly aligned CeO 2 cap on an IBAD–GZO layer and optimizing the conditions in the multi-coating process, respectively. For improving the production rate, the calcination time was extremely reduced by the development of the new combination of the starting materials. As the improvement of the production rate, the process for achieving high growth rate was investigated by controlling the atmosphere conditions in the high temperature heat treatment. It was found that both high humid partial pressure and low total pressure conditions were both effective to improve the growth rate and the three times higher growth rate with maintaining high J c than that in the conventional conditions was confirmed. Additionally, a 0.25 m long tape with uniform I c values over 200 A and the end-to-end I c value of 210 A was successfully fabricated with traveling in the furnace of the Reel-to-Reel system.

The YBCO layer of coated conductors is usually covered by a protective layer of metal such as silver. From the viewpoint of stability and quench protection, a thicker protective layer is preferable, but an increase in the thickness of the protective layer might result in an increase in the AC loss. In this work, pieces of YBCO coated conductors fabricated by the IBAD/PLD method are prepared, and silver layers of different thickness are placed on the samples. The magnetization losses of these samples are measured in a transverse magnetic field by the linked pick-up coil method. The orientation of the applied transverse magnetic field against the tape wide face, the frequency of the applied magnetic field, and the amplitude of the applied magnetic field are varied to study the influence of silver layer thickness on magnetization loss of YBCO coated conductors.

A 0.5 μm thick Gd 2 Zr 2 O 7 layer was deposited by the ion-beam-assisted deposition (IBAD) method on an Ni-based alloy (Hastelloy), and subsequently a 3 μm thick CeO 2 layer was coated by the pulsed-laser deposition (PLD) method. The in-plane alignment (Δ φ ) of the Gd 2 Zr 2 O 7 layer and the CeO 2 layer were 25° and 4.9°, respectively. TEM cross-sectional and plan-view specimens of the CeO 2 /Gd 2 Zr 2 O 7 multilayer were prepared for detailed microstructural characterization. It was observed that the Gd 2 Zr 2 O 7 layer has a columnar texture perpendicular to the Hastelloy tape surface. The columnar texture was composed of fine grains well aligned in the 〈0 0 1〉 direction. Therefore the boundaries of columns could not be observed clearly. In the CeO 2 layer, the nucleation process of CeO 2 grains on the Gd 2 Zr 2 O 7 surface was strongly affected by both the orientation relationships and the microstructures of the Gd 2 Zr 2 O 7 layer. As the CeO 2 grains grew from the Gd 2 Zr 2 O 7 surface, the in-plane alignment improved dramatically. The boundaries of CeO 2 grains could be observed clearly and were identified as small angle tilt grain boundaries.

YBa 2 Cu 3 O 7− δ (Y123) films were deposited under various water partial pressures ( P H 2 O ) in the crystallization process by the advanced metalorganic deposition (MOD) method using trifluoroacetates. Microstructures of the films were evaluated by means of transmission electron microscopy. As a result, in the Y123 film crystallized under lower P H 2 O such as 2.1%, large pores were remarkably observed. Furthermore, there were many amorphous layers of a non-superconducting phase in this film. In contrast, small pores were distributed in the films deposited under higher P H 2 O . Considering that the critical current ( I C ) values become higher as P H 2 O increases, existence of large pores and non-superconducting phase crystals causes to reduce I C . Through the investigation of the microstructure of the films quenched during the crystallization process, it was found that the pores in the film are generated by reaction of the non-superconducting phases, which are trapped in the growing Y123 film afterwards, to transform to Y123 with accompanied by the volume reduction of about 30%. The sizes of the entrapped phase crystals in Y123 film depend on the P H 2 O and it may determine the pore sizes in the final film.

The long tape process was developed using the advanced TFA precursor solution. In a long tape production, the advanced TFA precursor solution was coated by a die-coater using the reel-to-reel system, and the multi-coating method was applied for thicker film fabrication. We successfully fabricated long uniform precursor films. In the high temperature treatment, a large scale equipment for the continuous long tape process was developed. This equipment had a perpendicular gas flow system to the tape length which is effective to fabricate the uniform films. I c values and its distribution in the YBCO tape fabricated by this method on CeO 2 /IBAD-Gd 2 Zr 2 O 7 /Hastelloy were measured. And the uniform and high performance was confirmed. A 0.25 m long YBCO film with 1.38 μm in thickness on the metal substrate shows the high I c performance of 210 A with end to end at 77.3 K in self-fields.