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RASMES (Research Association of Superconducting Magnetic Energy Storage) in Japan developed a road map of SMES for fluctuating electric power compensation of renewable energy systems. Based on the progress of large superconducting coils, the technical status is already established to develop the several MWh class SMES for frequency control, load fluctuation compensation, and generation fluctuation compensation. With integrated operations of several dispersed SMES systems, it is expected that the 100 MWh class SMES for load fluctuation leveling (peak cut) can be introduced in the period of 2020-30, and the first 1 GWh class SMES for daily load leveling can be installed in the period of 2030-40. From the results of Japanese national projects, experimental device developments and SMES design studies, if the output power of SMES is 100 MW, the target cost of SMES can be evaluated with 2000 USD/kW of the unit cost per output power (the unit cost per kW).

Electrical insulation is one of the essential technologies for the electric power apparatus. Determination of testing voltages and design method of the electrical insulation layer are inextricably linked each other, and are critical to developing and realizing a cold dielectric (CD) type high-Tc superconducting (HTS) power cable. The authors had proposed the electrical insulation design method with concepts of partial discharge-free designs for ac voltage condition. This paper discusses the testing voltages for a 77 kV 1000 A HTS power cable with a length of 500 m, and describes results of various voltage withstand test. As a result, it is concluded that the proposed electrical insulation design method is appropriate for the HTS power cable.

A new proton accelerator complex for a high intensity beam (Japan Particle Accelerator Research Complex-J-PARC) is under construction at the Tokai campus of Japan Atomic Energy Research Institute as a joint project between KEK and JAERI. The accelerator complex is composed of a 600 MeV linac, a 3 GeV rapid cycling synchrotron, and a 50 GeV main synchrotron. In Phase I, the main synchrotron will be operated at energy of 40 GeV with pulse operation. The proton energy is to be increased up to 50 GeV in Phase II, and a large amount of pulse electric power, which is +115 MW and -55 MW peak-to-peak with 3.4-second repetition, will be demanded. Such large pulse power will give un-allowed disturbances to the power network. Some means will be required for compensating the pulse electric power and reducing the disturbances. A SMES system is one of the promising means. We have studied a SMES system for this purpose, designed the SMES coils using a force-balanced coil and a solenoid with a capacity of 100 MJ/55 MW, and proposed a new circuit scheme. The cost estimation of the SMES system is also described

MgB2 and high-temperature superconductors (HTS) are expected to reduce refrigeration energy requirements for superconducting coils. If MgB2 and HTS carry usable current densities at high magnetic fields, in contrast to NbTi superconductors, superconducting magnetic energy storage (SMES) systems will be realized in smaller coil dimensions and shorter conductor lengths. In this work, the design considerations for the SMES systems using MgB2 and/or HTS coils have been discussed. The required specifications of MgB2 and HTS coils with a liquid hydrogen cooling are: (1) the target critical current density of MgB2 and HTS should be higher than 1000 A/mm2 (w/o stabilizer) at 15~20 K and 5~10 T in order to improve small-sized SMES coils, (2) MgB2 and HTS coils require about 50-kA class superconductors with lengths of 5~10 km from the viewpoint of the coil construction, (3) the coil windings should be optimized in order to prevent a decrease in the operating current density within an allowable stress of MgB2 and HTS at high magnetic fields, (4) the force-balanced coil (FBC) is an optimal coil configuration that can enhance the operating current density and obtain the stored energy for the same current density about 100 times larger than that in the solenoid case by the effect of the minimization of the working stresses

Recently, the properties of high temperature superconducting tapes have been in advance and high temperature superconducting magnets have been constructed and demonstrated. However, the high temperature superconducting tapes have different thermal characteristics compared with low temperature superconducting wires. Therefore, it is necessary to consider these characteristics of high temperature superconducting tapes at the magnet design stage. We proposed an optimal design method for superconducting coils wound with Bi2223/Ag tapes. In this paper, the configuration of 72 MJ SMES coils wound with Bi2223/Ag tapes are optimized.

A high-temperature superconducting (HTS) power transmission cable is considered as one of the next-generation power transmission technologies. The introduction of HTS cables into the actual power grid requires a long-distance cooling tube, due to the location of the cooling stations at intervals of several kilometers along the cable length. Therefore, it is essential to understand the flow property of the liquid nitrogen as a coolant for the HTS cable, the current flow properties, electrical insulation characteristics, thermal insulation properties and mechanical behavior for the HTS cable taking into account its long length. This paper provides a brief summary of the HTS cable test system with a length of 500 m constructed in the Yokosuka area of CRIEPI.

A 500-m single-core high temperature superconducting (HTS) cable system has been constructed and tested in Yokosuka area, CRIEPI, by CRIEPI, The Furukawa Electric and Super-GM. In the actual power grid, the HTS cable distance extends sometimes several km. And has to be cooled down from about room temperature to liquid nitrogen temperature. As, the HTS cable is contracted and suffers mechanical stress. In the case of the long distance HTS cable, it remains a major development issue. The HTS cable constructed in this test system has an offset section for absorbing the thermal contraction. In this paper, we describe the validity of that offset section and the thermomechanical characteristics on the cooldown and warm-up test. The offset functioned successfully as designed.

High-T/sub c/ superconducting technology is thought to provide many merits for SMES systems. For example, a cryocooled system can be used as a cooling system for High-T/sub c/ superconducting coils, indicating that an operation temperature can be selected from a wide-temperature range below critical temperatures. Refrigerator cooling operation temperature for High-T/sub c/ SMES can be elevated more than 20 K from conventional 4.2 K. As a result, the heat capacity of coil system becomes much larger than that at 4.2 K, indicating that thermal diffusion time constant becomes much longer. If we could absorb transient heat generation with heat capacity of the coil, SMES systems can be designed under the over current state of critical current for a short duration. As a cooling capacity for an average heat load will be enough to cool High-T/sub c/ superconducting coil system for SMES, the refrigerator system cost can be much lower than that for a SMES system using Low-T/sub c/ superconductors. Moreover, we are developing high critical current superconducting wire for SMES system. The Bi2212 Rutherford conductors can carry 4 kA at 26 K under cryocooling. We also estimate the superconducting wire cost of the whole coil system, which is designed to minimize the superconductor volume. The conclusion is that the cost of High-T/sub c/ SMES system will be reduced by using the low-cost YBCO superconducting wires in the future.

Thermal behavior of high-temperature super-conducting (HTS) coil is exceedingly different from that of low-temperature superconducting (LTS) coil. Therefore for the sake of the application of HTS coil to practical use, establishment of a new stability criterion for coil design becomes indispensable. In this study, a small-sized cryocooler-cooled HTS coil wound with Bi-2223/Ag tape was constructed and tested to evaluate the electromagnetic and thermal characteristics in the cryocooler-cooled HTS coil. We carried out experiments subjected to pulse current operation supposing SMES for power system stabilization. The simulation by a newly developed computer program based on the finite element method (FEM) agreed well with experimental results. In the computer program, short-sample data concerning the E-J characteristics, which depend on the orientation of applied magnetic field to the wide face of Bi-2223Ag tape, was adopted. By using the computer program, we also evaluate the thermal behavior of HTS coil graded according to the magnetic field distribution.

REBa/sub 2/Cu/sub 3/O/sub y/ (REBCO) is expected to be used in numerous applications, such as power transmission cables, high-field magnets and generators, due to the possibility of a high critical current density at 77 K under a high magnetic field. Biaxially textured REBCO superconducting tapes are developed to obtain high-J/sub c/. However, the J/sub c/-B characteristics of REBa/sub 2/Cu/sub 3/O/sub y/ films have a magnetic field angle dependency. When the magnetic field is applied parallel to the film surface, the reduction in J/sub c/ is not larger under a high magnetic field of 10 T. When the magnetic field is applied perpendicular to the film surface, the reduction in J/sub c/ is significantly large under a magnetic field of more than around 5 T at 77 K. From the viewpoint of realizing wide applications of high-T/sub c/ superconductors, it is important to improve the J/sub c/-B characteristics of REBCO films under magnetic fields higher than 5 T applied perpendicular to the film surface. Our group focuses on artificial pinning centers (APCs) introduced into REBCO films. The J/sub c/-B characteristics of certain films are improved by the introduction of APCs. The microstructures of these films are investigated using transmission electron microscopy (TEM). We report on the microstructures of REBCO films with APCs.

High-Tc superconducting technology is thought to provide many merits for SMES systems. For example, a cryo-cooled system can be used as a cooling system for high-Tc superconducting coils, indicating that a wide range of operation temperatures can be selected. As a result, the heat capacity of the coil system becomes much larger than that at 4.2 K. If we could absorb transient heat generation with the heat capacity of the coil, SMES systems can be designed under the over-current state of critical current for a short duration. As the cooling capacity for an average heat load will be enough to cool the High-Tc superconducting coil system for an SMES, it is expected that refrigeration system cost can be reduced. Moreover, we are developing a high critical-current superconducting wire for the SMES system. The Bi2212 Rutherford conductors can carry 4 kA at 26 K under cryo-cooling. We also estimate the superconducting wire cost of the whole coil system, which is designed to minimize the superconductor volume. The conclusion is that the cost of a high-Tc SMES system can be reduced remarkably by using low-cost YBCO superconducting wires in the future.

A present Japanese national project for SMES development focuses on the development of cost reduction technologies for a small-scale SMES for power system control. Optimal SMES system concepts were developed for power system stabilization and for load fluctuation compensation or frequency regulation. Performance of the designed superconductors was analyzed through fabrication and tests of short sample superconductors. Then, two kinds of model coil systems were manufactured and tested for evaluation of the design concepts and cost reduction technology developments. A multi-pole solenoid coil set as a model coil system for load fluctuation compensation SMES was successfully tested, for example, in 10 000-pulse iterative charge–discharge operations. In addition, application of high- T C superconductors to SMES has been studied for further cost reduction, more reliable operation, etc.

Electrical loss-measurements were carried out in liquid nitrogen for long Bi-2223 tapes wound into a solenoidal-coil under various external conditions of ac transport currents and ac magnetic fields. In this experiment a new measuring-system, which is an extension of our original measuring-system applicable to short and straight HTS tapes, was developed. In this new system, the Poynting vectors at the outer and the inner surfaces of the sample coil were measured to get ac loss values by using two movable sets consisting of both a potential lead pair and a pick-up coil on each surface of the coil; The moving direction is the coil axis and its distance is one pitch of coil windings. Several samples were prepared in order to clarify fundamental electromagnetic-properties of Bi-2223 coils with various windings. The obvious difference of loss properties among these samples was observed for some external conditions of ac transport currents and ac magnetic fields.

Since 1999, a Japanese national project to realize commercially feasible SMES for designated applications has been promoted. Model coils for power system stabilization, load fluctuation compensation and frequency control have been fabricated and tested. In this paper, we introduce the present status of the project, including feasibility studies of an HTS SMES.

YBa 2 Cu 3 O 7− x (YBCO) is prepared by low-oxygen-pressure annealing of precursor films which are deposited from Y, BaF 2 and Cu sources at room temperature. In the annealing process, pure oxygen gas is introduced into the reaction chamber. The other gases, for example, water vapor or nitrogen gas, are not intentionally introduced. We previously reported that it is difficult to control the in-plane alignment YBCO films on MgO substrates. Therefore, a single cap layer (BaSnO 3 ) or double cap layers (CeO 2 /BaSnO 3 ) are deposited on the MgO substrate. Subsequently, the YBCO films are prepared on the cap-layer-buffered MgO substrates. We evaluated the crystallinity and the film growth of the YBCO films on single-cap-layer-buffered and double-cap-layer-buffered MgO substrates.

The research and development of superconducting magnet energy storage (SMES) system, a national project, began in 1999. One of the purposes of this project is investigation concerning the application of high-temperature superconducting (HTS) SMES. As a part of this project, the 3 kA class HTS small model coil was manufactured in order to verify the possibility of realizing conduction cooled HTS SMES. Therefore, it is important to develop the conduction cooled current lead system for applying this coil. We developed a kA class conduction cooled HTS current lead system. This current lead system consists of the copper current lead and the YBaCuO (YBCO) HTS current lead. The YBCO bulk manufactured by Nippon Steel Corporation was applied to the HTS current lead. The YBCO bulk keeps high critical current density ( J c > 10,000 A/cm 2 ) in the magnetic field (1 T) at 77 K compared with Bi2223 superconductor. The experiment of this HTS current lead system was carried out, and rated current of 3000 A was achieved successfully.

To achieve compact and highly efficient HTS power transmission cables, reducing and evaluating AC losses is important. However, measures of appreciable AC losses were uncertain using only the electrical method of evaluation. Therefore, a calorimetric device that had low heat leakage and high-resolution thermometers was developed. Using this device, measurement accuracy of AC losses in an HTS conductor was 0.09 W/m within a length of 3 m. The 4-layer 3 m long HTS conductor was fabricated with uniform current distribution in each layer by using variable-winding pitches and twisted filaments in the tape. Using the calorimetric device, we confirmed that AC losses in this conductor were 1 W/m level at 3 kA rms (50 Hz).

Precursor films are deposited on SrTiO 3 single crystals at room temperature by the co-evaporation technique using Y, BaF 2 and Cu as evaporation sources. Then, the precursor films are annealed in a low-pressure oxygen atmosphere without introduction of water vapor. A sample with a reflection high-energy electron diffraction (RHEED) pattern exhibiting some streaks, Kikuchi lines and Kikuchi zone, which resembles that of a single crystal, is successfully prepared. According to the cross-sectional TEM observation results, epitaxial growth of this YBCO film is achieved for the entire film thickness. The transport properties are measured using a small bridge with a width of 0.1 mm and a length of 1 mm by a standard four-probe method. The obtained YBCO film has a high J c of over 1 MA/cm 2 at 77 K and a self-field. Furthermore, we discuss the relationship between the epitaxial YBCO layer thickness and the annealing conditions. Approximately 300- and 400-nm-thick epitaxial YBCO films are successfully prepared.

The coating pyrolysis or metal organic deposition process is expected to be an attractive method offering the possibility of cost reduction and ease of large-scale fabrication of YBCO thin films. This process could realize a high critical current density of YBCO thin films. However the critical current density was measured only by the induced current method. Therefore, we compared the results of the induced current method with those of the transport current method. According to the measurement results, these values were almost the same as 2 MA/cm 2 , and a agreement between them was evident. The reaction between a YBCO film and indium contact and the change in quality of the YBCO film at the current contact point were examined. Because our experiments focused on large current applications such as the fault current limiter, reliable contact between the copper current lead and the YBCO film was essential. The difficulty of the large current measurement of the YBCO thin film was shown by our research.

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

To achieve compact and highly efficient HTS power transmission cables, reducing and evaluating AC losses is important. Furukawa is developing conductors with low AC losses of 1 W/m at 3000 Arms for the 66/77 kV class HTS cables as a part of the Super-ACE project. Specifically, we aim to achieve a superconducting conductor with minimum AC losses by optimizing the winding pitches and twisted filaments in the tape. The electrical method is generally used to evaluate AC losses in HTS cables. However, measures of AC losses were uncertain using only the electrical method of evaluation. Therefore, the calorimetric device was developed and was used for determining AC losses. Consequently, results from the two methods almost agreed. Moreover, AC losses in the fabricated HTS conductors were measured at the lowest levels ever achieved.

A new electrical system was developed for measuring ac losses of long HTS tapes or wires wound into a solenoidal-coil. This coil-loss measuring-system is an extension of our original ac-loss measuring system that is applicable to short, straight HTS tapes under various external conditions of transport currents and transverse magnetic fields, and is useful for fundamental studies of various windings of practical multi-layered coils. In this new system, the Poynting vectors at the outer and the inner surfaces of the coil were measured to get ac loss values by using two movable sets consisting of both a potential lead pair and a pick-up coil on each surface of the coil. The moving direction is the coil axis and its distance is one pitch of coil windings. The value of ac losses can be obtained by summation of the Poynting vector at many positions during the movement. The applicability of this system was confirmed by ac loss measurements on a solenoidal-coil wound loosely with Ag-sheathed, multifilamentary Bi-2223 tapes.

Transmission electron microscopy (TEM), reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) are used to characterize the microstructure and surface topography of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films. The YBCO films of approximately 0.2 and 0.8 /spl mu/m thickness are prepared by a post-annealing of precursor films of co-evaporated Y, BaF/sub 2/ and Cu. The annealing conditions are the same for all cases except for the temperature elevation rate. RHEED patterns corresponding to the YBCO structure are observed in both the samples after annealing at 700 /spl deg/C for 30 minutes. The XRD patterns show that both YBCO films have primarily c-axis orientation. According to TEM observation results, the YBCO film of 0.2 /spl mu/m thickness is epitaxially grown from a substrate surface. In the case of thicker films of 0.8 /spl mu/m, the bottom region of the film is epitaxial YBCO, while the top region is a mixture of a-axis orientation, other orientations and impurities.

High-Jc YBa2Cu3O7−x (YBCO) films on SrTiO3 substrates are successfully obtained by post-annealing of precursor films which are deposited by a co-evaporation technique with Y, BaF2 and Cu evaporation sources at room temperature. In the case of using fluoride as the starting material for YBCO fabrications, water vapour is commonly introduced to decompose the fluoride in an annealing process. However, in the present process, we intentionally did not introduce water vapour. The obtained YBCO films have a high Jc of over 1 MA cm−2 at 77 K and a self-field. This work has demonstrated that the additional water vapour is not required to obtain a high-Jc YBCO film regardless of whether fluoride is used as a starting material or not.

For the optimization of electrical insulation design for high temperature superconducting (HTS) cable, evaluation of electrical insulation characteristics especially for butt gap of LN/sub 2/ impregnated cold dielectric (CD) which consists of the wrapped tape insulation impregnated with LN/sub 2/ plays an important role. This paper presents partial discharge (PD) inception and breakdown characteristics in LN/sub 2/ impregnated butt gap model which modeled a weak point of the wrapped tape insulation impregnated with LN/sub 2/ and cable model with short length with polypropylene laminated paper (PPLP/sup /spl reg//), Nomex/sup /spl reg// paper and cellulose paper. PD current pulse was found to have a steep rise time of /spl sim/ ns and amplitude of /spl sim/ tens /spl mu/A at PD inception voltage region. Little dependency of breakdown stress on the insulating material is found. PD inception stress is almost independent of insulation thickness of 1 to 3 mm. The requirement insulation thickness for 66 kV class HTS cable is estimated to be /spl sim/ 5 mm under PD-free condition from viewpoint of long-term reliability.

We measured the AC transport current losses in Bi2223/Ag sheathed tapes stacked laterally with gaps between the tapes, wide faces of a tape facing to those of the other tapes. The data were compared with the AC transport current losses in isolated Bi2223/Ag tapes and also with those in Bi2223/Ag tapes arranged in a single flat layer with the wide faces of the tapes on a flat plane. The experimental results showed that the AC transport current losses in the tapes laterally stacked were higher than those in the isolated tapes and those in the tapes arranged in a single flat layer. Reason for those results is studied by considering that the current distribution in the tapes is affected by the magnetic fields produced by the neighboring tapes.

R&D priorities of superconducting power apparatuses were investigated by NEDO sending questionnaires to experts in the field of superconductivity applications. As a result of the investigation, superconducting generators with low temperature superconductor superconducting field windings, high temperature superconductor (HTS) power cables, HTS fault current limiters and HTS transformers had high R&D priorities and are expected to come into the real applications in the years of 2011–2015. Based on this result, the government decided to raise three national projects in the year of 2000 to develop those apparatuses together with flywheel energy storage. Beside of those three projects, there are two more national projects for fundamental material technology developments for HTS applications (raised in 1998) and R&D of SMES (raised in 1998). Important results are coming out now, though most of the projects are in early stage of the project term.

To survey the applicability of existing HTS wires for SMES, five kinds of cryocooler-cooled HTS coils were fabricated and tested to estimate fundamental characteristics of HTS wires. Critical current, run-away current, and ac losses were measured. To confirm the effect of electromagnetic force to the coil performances, critical currents were measured under high magnetic fleld of 14 T with liquid helium cooling. The HTS wires used for the coils are three types of Bi2212 wire and two types of Bi2223 wires. We have wound these wires to little coils of 14 cm outside diameter, 10 cm height with cryocooling. As a result, a difference of critical current characteristic of a Bi2212 wire and a Bi2223 wire was not big at the temperature of 20 K, but a critical current of a Bi2212 wire fell at 50 K greatly, and the HTS-SMES design that utilized a temperature margin by cryocooler-cooled system understood what a Bi2223 wire was suited for.

Precursor films were deposited by the co-evaporation technique using Y, BaF2 and Cu as evaporation sources. Then, the films were annealed at low-pressure oxygen atmosphere without the introduction of water vapour, which was different from the so-called BaF2 ex situ process. Previous studies have indicated that the c-axis-oriented YBCO films can be prepared by annealing at low-pressure oxygen atmosphere, and that the reaction of the precursor films during sample temperature elevation is very important in the present process according to reflection high-energy electron diffraction (RHEED) observation. Therefore, two kinds of samples, rapidly cooled down from 400 °C and 630 °C, were prepared for microstructural study. YBCO film growth in this process is discussed on the basis of the results of x-ray diffraction (XRD), RHEED and transmission electron microscopy (TEM).

HTS-SMES has high potential to increase efficiency and future cost reduction. Therefore, MITI started new national project on feasibility study of HTS-SMES in FY 1999 for five-year project, as a sub-program of LTS-SMES cost reduction project, that is a succeeding project of 100 kW h SMES key technology development to FY 1998. In FY 1999, parameter survey has shown that 15 kW h class HTS-SMES can be realized by both of Bi-2212 and Bi-2223 wire operated at around 20 K with reasonable sizes by conduction cooling. As for Y-system wires, operating temperature around 77 K is rather high to have magnetic field to store enough energy. Lower temperature operation was suggested. Mechanical strength tests on Bi-2212 Rutherford cable revealed that they could withstand tensile strain up to 0.6% without I c degradation. This allows high flexibility in mechanical design of HTS-SMES.

We investigated the AC loss properties of a Bi-2212 Rutherford-type cable with large current capacity for future SMES. The cable is composedof 20 strands with a diameter of 0.8 mm and reinforced by Ni based alloy, which is located in the center of the cable. The width and thickness of cable are 9.05 and 2.25 mm respectively. The strand has 61×7 filaments and the average diameter of the 61 filament bundle is about 0.2 mm. The critical current of the cable is about 2.9 kA at 4.2 K and 0 T. We measured the AC losses in the strand and the cable at 4.2 K by pick-up coil method. The AC loss in the strand was scarcely dependent on frequency since it was not twisted. On the other hand, the AC losses in the cable had remarkable frequency dependence. It may be due to the coupling current between strands. We quantitatively discuss the AC loss of the cable in comparison with theoretical evaluation.

We studied the feasibility of a cryocooler cooled 15 kW h HTS-SMES for system stabilization. HTS magnets will have better properties at high magnetic field than do LTS magnets, the volumes of HTS magnets are expected to be reduced. In the study, we calculated volumes, flux-flow losses and ac losses of various shapes of the HTS magnets at a settled load factor and found that more than 10 T of maximum applied field to the magnets should be selected for the cryocooler cooled 15 kW h HTS-SMES magnet designs.

Parameter survey is performed to obtain shape and fundamental specifications for the 15 kW h/100 MW power system stabilizing superconducting magnetic energy storage. Using the scaling law for ideal toroidal coils and J c – B characteristics of several high temperature superconductors, three fundamental specifications to minimize amount of the superconductor are obtained. In the results the optimum parameters of Bi are 4.2 K–16 T for Bi2212 (tape) and 20 K–10 T for Bi2212 (tape). And the optimum parameter of Y123 is 2 T under the condition of 77 K. But Y123 is expected to have another optimum parameter in lower temperature. Assuming an actual conductor shape, structural analysis is performed in the typical case of 4.2 K–16 T. In result, the reinforcement member area is obtained.

Bi-2212/Ag Rutherford cable is expected as a high temperature superconducting magnet for SMES use because its critical current is 3.5 kA at 0 T, 4.2 K and it has the structure of enduring large magnetic force. Tests on the relation of critical current and tensile strain of the strand were performed. It was confirmed that I c and n -value began to decrease when the tensile strain of the strand increased over 0.6%. The share of the load between the strand and the Ni-base metallic core was found by examining the strength of the strand and the cable, and evaluating them with the above data. It was considered that the critical stress of this Rutherford cable was nearly 240 MPa which was necessary to design 20 T-class magnet.

YBa 2 Cu 3 O 7− x (YBCO) films are prepared by the deposition of precursor films including BaF 2 followed by annealing under a low-pressure atmosphere. In the present process, water vapor is not introduced in the reaction chamber. Pure oxygen gas is introduced near the sample and the background pressure is kept at about 2–9×10 −4 Torr. As a result, the c -axis-oriented YBCO films are successfully prepared on the Y 2 O 3 buffered (1 0 0)SrTiO 3 single crystal and the (1 0 0)MgO single crystal. The in-plane FWHM of (1 0 2)YBCO on the Y 2 O 3 -buffered SrTiO 3 is about 1°, indicating that YBCO films grow epitaxially and the crystal growth occurs from the interface between a precursor film and a substrate. Meanwhile, the in-plane alignment of YBCO films on (1 0 0)MgO substrates so far obtained is poorer than that of the YBCO film on Y 2 O 3 buffers, which depends on the annealing pressure and direction of oxygen introduction.

A multifilamentary Nb3Sn composite conductor for AC use was fabricated by the internal tin-core method. In this conductor, Nb–1at.%W is used for filaments and Cu–1at.%Ni for matrix. The conductor has 33,252 filaments of a diameter of 0.36 μm. Samples of conductor were heat treated at 450–700°C for 24–740 h and the critical current and magnetization were measured at 4.2 K in transverse fields up to 5 T. Overall critical current density of 4.9 GA/m2 at 1.5 T is obtained with a heat treated at 600°C for 200 h. The effective filament diameter was estimated to be 3–5 μm at 1.5 T.

A fluoride compound, BaF/sub 2/, was used in the ex situ post-reaction process which was effective in the preparation of thick YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films over 1 micrometers for coated conductors. We investigated the YBCO film growth on SrTiO/sub 3/ single crystal with and without Y/sub 2/O/sub 3/ buffer layers using BaF/sub 2/. In order to suppress the reaction between the YBCO precursor films and the Y/sub 2/O/sub 3/ buffer layer, we controlled the atmospheric pressure and changed the evaporation materials to obtain precursor films which included fluoride. No water vapor was introduced during the heat treatment. The epitaxy c-axis oriented YBCO films, with 0.3 /spl mu/m thickness, were successfully grown on both the Y/sub 2/O/sub 3/ buffered and nonbuffered SrTiO/sub 3/ single crystals using Y, BaF/sub 2/ and Cu as evaporation sources. We also deposited YBCO films on both substrates using evaporation sources, YF/sub 3/, Ba and Cu. An appreciably different result has been obtained using YF/sub 3/ compared to that using BaF/sub 2/.

YBCO tape is highly promising as a 2nd-stage HTS conductor for power applications, and development of long tape is proceeding worldwide. Generally, HTS tape conductors have broad transition characteristics ranging from the superconducting state to the normal state, so they rarely quench just above the critical current defined for a usual electrical field or resistivity. However, such characteristics make the stability criteria complex when these tapes are considered for power applications. To estimate the stability criteria of HTS tapes, we prepared YBCO tapes with YSZ textured buffers by the IBAD method. The thickness, width and length of the YBCO layer are 1 /spl mu/m, 10 mm and about 140 mm, respectively, and tapes are coated with Ag of various thicknesses as a stabilizer and protector. Transport current properties are measured in a wide range of current above the critical current defined by 1 /spl mu/V/cm. The establishment of criteria to define the stability of HTS tapes will be necessary for their applications in power apparatuses.

Two kinds of Y2O3 buffer layers have been directly deposited on cube-textured Ni substrates by electron beam evaporation under different gas pressures. One is deposited at 10-5 Torr air (a single-layer buffer). In order to reveal the improvement of the microstructure, the other is formed at first under 5×10-4 Torr and then 10-6 Torr of N2 (a double-layer buffer). As a result, the double-buffer layer obtained is more than 97% {100} orientation and is a relatively denser structure. YBa2Cu3O7-x overlayers are deposited by pulsed-laser deposition on these buffer layers. Large YBa2Cu3O7-x pop-off areas are seen for the single-buffer samples. These areas are eliminated on the double-layer buffer. However, the critical current does not increase appreciably for the YBa2Cu3O7-x film on the double-layer buffer, even though the microstructure of the buffer is improved. Other defects probably yielded percolative current flow and a low critical current density in the YBa2Cu3O7-x layers.

Y 2 O 3 films were deposited on cube-textured Ni substrates by electron-beam evaporation as part of a buffer layer study for YBa 2 Cu 3 O 7− δ (YBCO) coated conductors. Their microstructure was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their crystallographic texture and surface roughness evaluated by X-ray diffraction (XRD) and atomic force microscopy (AFM). Previous studies showed the Y 2 O 3 surface normal changed from {100} to {111} on decreasing the deposition chamber pressure from 10 −5 to 10 −6 Torr. In this work, 300 nm thick Y 2 O 3 buffer layers were deposited at two different deposition chamber pressures, ∼5×10 −4 Torr N 2 and ∼2×10 −5 Torr air, so as to make the {100} orientation dominant. However, the morphology of the Y 2 O 3 buffer layers was significantly affected by changing the deposition chamber pressure, the lower pressure buffer layer being denser and smoother than that made at the higher pressure. The Y 2 O 3 grains in a 600 nm thick Y 2 O 3 buffer layer grown under 2×10 −5 Torr air became larger and more uniformly square as the film grew thicker. The Y 2 O 3 grown on thermally grooved Ni deposited at 2×10 −5 Torr air, showed 〈111〉-oriented grains near the grooves. This local imperfection in the texture could lead to significant barriers to supercurrent flow in the YBCO overlayer.

In order to apply high T/sub c/ superconducting (HTS) tape to the power apparatus, it is necessary to evaluate the property of the coil shape. In particular, the stability of the coil is important, because it is expected to influence both the machine design and the operating conditions. In order to study the feasibility of HTS power application, they used double-pancake coils wound by Ag-sheathed Bi-2223 multi-filament tapes, and measured the transport current properties. From the experimental and analytical results, it was noted that the HTS double-pancake coils exhibited very stable properties, even beyond the critical current of coils. They believe that they can show the possibility of application of the HTS tape to the winding of power apparatus, although further improvements in superconducting properties of the tapes are needed. The stabilities of HTS and LTS (low T/sub c/ superconductor) are quite different, so it is also necessary to establish an analytical method for determining the stability of HTS winding.

The direct deposition of Y/sub 2/O/sub 3/ buffer layers on cube-textured nickel tape was successfully performed by electron beam deposition using Y metal which oxidized during deposition. The Y/sub 2/O/sub 3/ layer exhibited excellent out-of-plane alignment of FWHM of 2.3/spl sim/4/spl deg/ and good in-plane alignment with /spl sim/11/spl deg/ FWHM. Surface morphology, crystal orientation and grain size proved to be quite sensitive to the deposition pressure. The surface roughness and the grain size increased with increasing deposition pressure, and the crystal orientation changed from [111]Y/sub 2/O/sub 3/ to [100]Y/sub 2/O/sub 3/. Subsequently, YBCO superconducting films were deposited on [100]Y/sub 2/O/sub 3/ buffer layers by co-evaporation deposition and pulsed-laser deposition (PLD). Though a good in-plane alignment, as measured by X-ray /spl phi/-scan, was achieved in the YBCO films, their superconducting characteristics were not so good. The T/sub c/ onset was about 84 K for the [001]YBCO by PLD. The crystal alignment and the microstructure of YBCO superconducting films deposited by the two deposition techniques on cube-textured Ni tapes with Y/sub 2/O/sub 3/ buffer layers are compared.

Biaxially aligned Y2O3 layers useful as buffer layers for high-Tc oxide films have been synthesized on metal tapes through a new and simple method. The Y2O3 buffer layers are deposited on biaxially-textured Ni substrates by an electron beam evaporation technique using Y metal as the evaporation source, and controlling the pressure of the deposition chamber. The obtained Y2O3 films are strongly oriented in-plane and out-of-plane. The φ scan through the Y2O3(222) peaks reveals clear fourfold in-plane symmetry and the in-plane full-width at half maximum (FWHM) of 10.9°. The rocking curve through the Y2O3(400) peak reveals the out-of-plane FWHM of 2.3°. The metal tapes buffered by Y2O3 may be served as long and flexible substrates for high performance biaxially-aligned high-Tc oxide tapes.

A Nb/sub 3/Sn superconducting cable for use as the field winding conductor of a superconducting generator was developed with the in-situ process. A magnetic field of up to 7 T, and a transverse compressive mechanical force of up to 29.4 MPa were applied to the conductor, and the critical current and strain of the cable were measured. A cyclic compressive mechanical force was also applied in order to simulate DSS operation of the generator for up to 30 years. Over 10,000 loading cycles, the critical current showed no degradation and was constant. By changing the magnetic field direction while maintaining the current direction, both compressive and tensile electromagnetic stresses were applied to the cable, and the critical currents were measured under both conditions. The critical current under compressive stress was smaller than that under tensile stress. Thus, it became apparent that electromagnetic strain must be considered when measuring the critical current of large current capacity Nb/sub 3/Sn superconducting cables.

For implementation of AC superconducting equipment, it is imperative to develop low loss cables having highly stable characteristics. Here, newly developed NbTi superconducting cables using a CuSi alloy matrix are of low loss and are very promising as cables for practical application. However, since the CuSi alloy is a new material as a matrix for NbTi superconducting cables, many unknown factors as regards to optimum conditions for the manufacture of long cables, as well as superconducting characteristics are involved. For this new superconducting cable, a long strand (km class) was manufactured as a step for practical application, and a primary twisted cable was fabricated. Using this cable, a coil of the 100 kVA class was fabricated for trial, and its performance characteristic with transport current was evaluated. This coil had no training phenomenon and had a high stabilities. Furthermore, it permitted full AC current transmission of up to DCIc. Upon analysis of the coil loss, the hysteresis loss was smaller than coupling loss, and there was little increase of loss due to the current flow to the coil. Consequently, by using CuSi alloy matrix superconducting cables, it was possible to provide an AC coil of low loss and high stability, and the present cable was found to be promising as a new AC superconducting cable in the future.

The Nb/sub 3/Sn superconductor possesses a higher critical temperature than the NbTi strand. Therefore, it is now possible to make highly stable superconducting strands. We examined the manufacturing process of AC Nb/sub 3/Sn strands. The internal Sn diffusion process showed a higher critical current density than the conventional process. Nb/sub 3/Sn strands for AC use have a high Jc with low temperature reaction heat treatment, because they have fine filaments to decrease AC loss. We made a 400 kVA class superconducting coil using the developed Nb/sub 3/Sn cable with the React and Wind method. The loss density of this coil was 25.7 MW/m/sup 3/ at the point just before the quench. In this case, the temperature of the cable increases about 3.39 K. This means that the coil using Nb/sub 3/Sn cables has a very high stability in AC use.