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We have been developing high-strength Nb3Sn strand cables to construct a high-field superconducting outsert for a 45 T hybrid magnet with a 25 T water-cooled resistive magnet. Evidence for cold work strengthening of repeated bending treatment (prebending effect) on Nb3Sn strands internally reinforced with CuNb stabilizer, which exhibits significant enhancement of the critical current density, has been found in the superconducting magnet fabrication process using a react-and-wind method. The strand cables were designed by controlling the constituent number of CuNb/Nb3Sn strands with the prebending effect and stainless steel strands, which are expected to have a stress limit 580 MPa at 0.4% strain. In order to design a compact superconducting outsert, high-strength strand cables are adopted in a magnetic field region below 14 T to maintain relatively large engineering current densities (Je). In a higher-field region above 14 T, YBa2Cu3O7 (Y123) coated conductors are employed for an insert coil. Using combination of Y123, Nb3Sn and NbTi superconductors, a 20 T superconducting outsert with a room temperature bore of 400 mm consisting of three layers made of Y123, two layers of CuNb/Nb3Sn and two layers of NbTi was designed. The coil parameters are 440 mm inner diameter, 1080 mm outer diameter and 1138 mm coil height. A very compact 20 T superconducting outsert with a stored magnetic energy 72 MJ at an operation current 903 A can be developed for a 45 T hybrid magnet.

The High Field Laboratory for Superconducting Materials (HFLSM) and the Tsukuba Magnet Laboratory (TML) conducted in collaboration a case study on development of a 50 T-class hybrid magnet. To construct a high magnetic field magnet with compact and energy-saving design as well as with easy operation and maintenance, one has to develop high-strength NbSn strand cables, with maximized superconducting characteristics and which can withstand a large electromagnetic force over 500 MPa. For this purpose, the HFLSM has proposed and investigated the effect of repeated bending treatment (pre bending) on NbSn strands internally reinforced with CuNb stabilizer leading to significant enhancement of the critical current density. In this report we present our results on application of the pre bending effect to the development of high-strength strand cables. The designed prebent-strand cables are composed of three CuNb/Nb3Sn strands (3 times Phi =1.73 mm) and four stainless steel strands ( 4 times Phi =1.73 mm). High-strength CuNb/Nb3Sn strand cables have shown a stress limit of 552 MPa at 0.4% strain, and a critical current of Ic =1000 A at 18.5 T and 2.0 K. For such high-strength strand cables, a 20 T superconducting magnet with a room temperature bore (Phi =400 mm) consisting of five layers made of CuNb/NbSn and two layers of NbTi was designed. The coil parameters are: inner diameter Phi = 440 mm, outer diameter Phi = 1332 mm, coil height 1321 mm, inductance 350 H and magnetic stored energy 144 MJ at 908 A of the operation current. Winding of the coil was experimentally successfully simulated using dummy 3 + 4 strands cable composed of three Cu strands and 4 stainless steel strands with a similar design to the 3 + 4 strands superconducting cable presented above. The 20 T superconducting coil will be used as a 20 T outsert for a 25 T water-cooled resistive insert to obtain a 45 T hybrid magnet.

The long term reliability of the SMES model coil for the 100 kWh SMES pilot plant was investigated in a 1000 cycles cyclic test in the test facility of the Lawrence Livermore National Laboratory (LLNL) in 1998, in collaboration between Japan and the USA. The coil parameters such as coil inductance, magnetic field and AC loss were measured before and after the cyclic test. They did not change. The coil was successfully charged up to 40.53 kA in the mechanical performance test, which gave mechanically the same conditions as in the SMES pilot plant at rated current. After all performance tests, the coil was checked visually and electrically, and no degradation was observed. Mechanical reliability of the SMES model coil was verified in the performance tests. The obtained technical results encourage recommendation of the construction of the pilot plant.

SMES has a high potential for application in power utility, because of high plant efficiency, quick response, and power controllability. SMES is composed of a superconducting coil, vapor-cooled leads, and a power conditioning system. The electrical specifications for SMES are discussed on the basis of input and output power depending on size and application. As breakdown voltage in helium gas is low, an internally cooled magnet system is preferable to a pool boiling one. A model coil for a 100 kWh SMES, which is a typical forced cooled magnet system, was developed in Japan and then successfully tested. A glass–polyimide–glass tape insulation system was investigated in view of electrical and mechanical strength prior to fabrication. The breakdown voltage measurement of a sample with an artificial crack showed sufficient strength. The insulation critical fracture strength has a good agreement with the Mohr–Coulomb criterion.

The transverse resistance among strands of multi-stage twisted cables is one of the most important parameters to decide the stability and the AC losses. This value is varied with the cable compression affected by the void fraction or the Lorentz forces under charging. Furthermore it is also influenced by cyclic number of transversal compression. This paper describes the basic mechanical property of the chrome plated NbTi cable for the transverse compression, and the relation of the transverse resistance and the internal loads of the cable by measuring the impedance and the rigidity for various internal loads. It shows that the transverse resistance, which is much influenced with the performance of conductor, is always changed corresponding to the compressive load and dose not indicate the same resistance after release from the compression because of its elastic hysteresis.

Stability margin of the Cable-in-Conduit Conductor used under the pulse field is greatly influenced by inter-strand coupling losses and current unbalance with coupling current among strands. The large transverse resistance trades sufficient current transfer among strands for low AC losses. The large stability margin is brought by sufficient current transfer, low AC losses and uniform current distribution. Then we should decide the reasonable value of transverse resistance corresponding to the pulse condition. In this paper, the stability is estimated by the simplified distributed constant circuits simulating unbalanced current, that is transient coupling current, and transfer current among strands. In the non-insulated strands, the inductive voltage occurred during charging in a twisted area of half pitch must be enough lower than normal voltage of local quench at the limiting current. This paper also shows that the short twisted pitch and long cables about 1000 m give not only low AC losses but also uniform current distribution during charging for insulated strands.

The relationship between stability of superconductor and structure of the cable-in-conduit (CIC)-type conductor is discussed by studying the simple estimation of work by strand movement and results of stability tests of small coils wound by five kinds of CIC-type NbTi conductors. The allowable thermal disturbance energy not to quench the coil is estimated. When the strands are electrically insulated, the stability of the CIC-type conductor is low because of inhomogeneous current distribution among the strands. On the other hand, when the strands are not insulated, the conductors are stable until the thermal disturbance energy approaches the helium enthalpy rise from bath temperature to the temperature of current sharing because of quick current transfer to other strands.

Dry-wound superconducting solenoids offer good manufacturability of large bore magnets but occasionally suffer from premature quenches triggered by small heat generated within the magnets. The principal source of heat is thought to be conductor motion induced frictional heating and/or filler material fracture released energy in windings. This paper describes major specification, stress analysis and training performance and their relation to a series of magnets that were constructed and tested to establish stabilizing methods of a large bore dry-wound superconducting solenoid. The results suggested that conductor motion took place even though radial stress in the magnet was still compressive and a conductor was expected in its original position. >

The stability margin of CIC multi-strand superconducting cables under partial current distribution is affected by electrical resistance among the strands. This means that the stability is governed by the current sharing process among the strands. The achievement of high stability against partial current distribution will be realized by rapid current transfer to the other strands rather than by thermal diffusion of Joule heating to helium. A simplified electrical circuit model, that is a distributed constant circuit for two strands, simulating the current sharing process between strands, is proposed to estimate the stability. The results of the stability analysis, clarify the limiting condition to maintain stability. The circuit constants governing the sharing process can be investigated from the frequency properties of a characteristic impedance measured with CICC short samples. These results are confirmed with experimental results of stability tests under partial current distribution. The proposed estimation method is viable. >

The stability and limiting current of a NbTi forced-cooled superconducting coil have been investigated experimentally and analytically at the subcooled condition below 4.5 K. The test coil was wound in a one layer solenoid from a cable-in-conduit type conductor of critical current of 5.1 kA at 4.2 K and 6.5 T, whose total length was 10 m. It was installed in the bore of a back-up superconducting magnet that provided field 8 T at the test coil. The stability margin of the coil as a function of normalized current (transport current/critical current) were measured. The results are compared with the formula proposed by Dresner and reported to predictions of stability margin and limiting current at subcooled condition below 4.5 K. >

Low AC loss and high current density NbTi/Cu/CuNi double stage cabling superconductor for quick response superconducting generator (SCG) has been developed. Its characteristics were measured by short sample and several coil models. The critical current of 14 kA at 6 T and the AC loss of 10 kw/m/sup 3/ were achieved, and coil models were excited under high current change rate operation without the quench. The developed superconductor will be able to be applied to a 70 MW class quick response SCG. >

A forced-cooled superconducting coil has been studied for the next step fusion machines because of many merits. The coil can be cooled by supercritical helium below 4.5K, which improves the stability and other superconducting characteristics. To study the stability of the coil at lower temperature, a test coil wound in a one-layer solenoid with a CIC conductor was tested below 4.5K. It was proved that the stability at lower temperature would be able to predict from the relationship between the critical current below 4.5K and the stability characteristics at 4.5K. The limiting current at lower temperature is in good agreement with the Lottin's experimental results.

In this research, after the simulation of FEM analysis using the three dimensional concrete model, we focused on the large dispersion of the transmitted echo in concrete due to the velocity difference between aggregate and mortar. Then to support the efficient measurement for this large dispersion the super‐broad band ultrasonic measurement system using step function pulsar combined with the broad band transducer of 500 kHz in frequency was applied for the transmission and reflection measurement of the concrete specimen with a thickness of 200 mm. Furthermore, the spatial averaging measurement procedure for a virtual larger transducer was applied as a basic research of the ultrasonic evaluation for industrial concrete structure.

A forced-cooled superconducting coil (DPC-TJ) was wound with a double walled cable-in-conduit referred to as preformed-armour type C ICC. In this paper, we describe the fabrication of the conductor for the DPC-TJ coil with the first conduit, which plays a role in sealing the supercritical helium from the vacuum. Because the DPC-TJ coil has a high average current density of 40 A mm−2 (12 T,4.2 K) in the winding area, an (NbTi)3Sn strand formed by the Nb tube method was selected, which has a very high critical current density in the non-Cu area. As a result of development work, a strand could be fabricated which met the following requirements: critical current density > 600 A mm−2 at 12 T and residual resistivity ratio (RRR) value > 50. A fabrication line for the cable-in-conduit conductors using the roll-forming method was also developed. Through fabrication of the conductor for the DPC-TJ coil, it was demonstrated that large and long conductors could be fabricated for future fusion reactors.

A 40 A mm −2 , 24 kA, high rigidity, large forced-cooled, (NbTi) 3 Sn superconducting coil referred to as the DPC-TJ was developed during collaboration between the Japan Atomic Energy Research Institute and Toshiba Corporation. The purpose of the DPC-TJ Program is to demonstrate the realizability of a high average current density with a large coil wound by a large Nb 3 Sn superconductor which meets the requirements of the conductor for the next thermonuclear fusion machine. The DPC-TJ was fabricated as the first coil of the preformed-armour type, which was developed in this programme as a fabrication method that enables us to achieve high rigidity and high current density simultaneously without difficulty. Testing of the DPC-TJ coil was performed successfully and the DPC-TJ Program was completed having accomplished its objectives.

The disturbance energy of a forced flow cooled superconducting coil (FCC) is discussed. The authors built a FCC and carried out stability and quench tests. The test coil had a 36-m-long cooling path with a 0.37-mm hydraulic diameter. It was cooled by supercritical helium at 4.1 K. The stability margin of the FCC was evaluated by using RF heating. In addition, the coil quench test was performed. The disturbance energy at quench is estimated by the stability margin characteristics. The disturbance energy obtained agrees well with that of a simple analytical model. >

The DPC-TJ test coil was developed in the collaboration between the Japan Atomic Energy Research Institute (JAERI) and Toshiba for the Demo Poloidal Coil (DPC) project at JAERI to obtain key technologies required for the construction of superconducting coils of a fusion experimental reactor. The DPC-TJ is a 1-m-bore, 40-A/mm/sup 2/ forced-flow cooled superconducting coil wound with a double-walled 24-kA, 12-T (NbTi)/sub 3/Sn cable-in-conduit conductor. The DPC-TJ was tested to investigate stability performance at operating conditions between 15 kA, 2.3 T and 30 kA, 4.5 T. Another test was carried out with a 1/18 reduced-scale model of the DPC-TJ conductor to investigate stability margins at the designed field of 12 T. Results indicated the limiting current of the DPC-TJ was around 25 kA. The DPC-TJ coil was stably charged up to 30 kA without any normal transitions because only a small mechanical disturbance could occur in the newly developed type of conductor. >

The stability and quench characteristics of a NbTi forced-cooled superconducting coil at the subcooled condition were investigated. The test coil was wound in a one-layer solenoid from a cable-in-conduit-type conductor of 1.5 kA at 7 T, whose total length was 34 m. It was installed in a background coil and tested between the subcooled condition below 4.5 K and the normal condition above 4.5 K. Stability, quench current, normal propagation velocity, and pressure rise during a quench of the subcooled coil were measured. The stability margin increased and the pressure rise during a quench decreased as the inlet coolant temperature was lowered. >

A force-cooled superconducting coil has been studied for the Large Helical Device (LHD), which will be a main experimental apparatus of the Japanese National Institute for Fusion Science (NIFS). To achieve the main requirements for the LHD, a large-current, high-current-density NbTi cable-in-conduit-type conductor of 10 kA and 47 A/mm/sup 2/ at 8 T was developed. The test coil was wound in the form of a one-layer solenoid and tested at an operating current of 10 kA in a superposed field of about 7 T, at a hydraulic condition of 1.0 MPa, 4.5 K, and 10 g/s supercritical helium. The stability, normal propagation velocity, and pressure rise during a quench for the high-current-density case were also studied.

A polycrystalline silicon (polysilicon) plug was developed for the planarization of high-aspect-ratio contact holes. Using this method, the authors realized a low contact resistance of 118 Omega on p-type and 57 Omega on n-type diffusion layers for 0.6- mu m hole diameter and 0.8- mu m hole depth. Moreover, a shallow source/drain junction of 0.15- mu m depth using rapid thermal annealing (RTA) was obtained. The key issues in this technology are the double (low- and high-energy) ion implantation of boron for the p-type plug and low-temperature insertion and subsequent deposition of polysilicon and dopant activation by RTA in the plugs and diffused layers at the same time. >

In recent years, many types of Intelligent Power Devices (IPDs) have been developed. A key technology of developing the IPDs is the isolation between power device and control circuit. The isolation structures and its manufacturing methods are required to be more efficient and cost effective. We had been developed a low side switch IPD having Vertical DMOSFET (VDMOS) output by using poly-crystalline silicon sandwiched wafer bonding (PSB) technique. In this PSB structure, it is easy to achieve void-free bonding because the extremely flat poly-crystalline silicon (poly-Si) layer surface and the single-crystalline silicon (Si) substrate surface are bonded together. However, the PSB structure is still expensive. To reduce the fabrication cost, we have made a study of the direct bonding without poly-Si and proposed a new SOI structure named partially bonded (PB) structure. This paper reports the evaluation results that we applied the PB structure to a low side switch IPD for the first time.

A new simple isolation structure has been realized by using poly-Si sandwiched wafer bonding technique. We confirmed that the poly-Si layer enabled the bonded interface to be void-free and electrically perfect, and had the effect that it enabled the reverse recovery time of the parasitic diode of Vertical DMOSFET (VDMOS) to be short. In the new structure, the isolation capabilities were adequate to integrate 60 V VDMOS and control circuits on the same chip. Especially, the parasitic bipolar action has been suppressed. We evaluated an intelligent power device which uses this technique and have confirmed the availability of the new isolation structure.

Intelligent power ICs with vertical double-diffused MOS (VDMOS) output devices are used for solenoid controlled applications. Many structures have been proposed for these power ICs. We have developed poly-Si sandwiched bonded (PSB) structures which use a Sb doped poly-Si and crystal-Si bonding technique. However these PSB structures have a high fabrication cost, because the fabrication process includes Sb diffusion into poly-Si layers. In this paper, we first propose an improved fabrication process of PSB structures without Sb diffusion into poly-Si layers. Second, we propose a new SOI structure with gaps fabricated by a wafer direct bonding technique. Both structures enable us to obtain low-cost intelligent power ICs with VDMOS.

The properties of Nb3Sn cable-in-conduit conductor were investigated experimentally with the void fraction and the cross-sectional shape as the parameters. As the result of a series of experiment, it was concluded that the critical void fraction value existed between 40% and 36% from both viewpoints of instability and critical current degradation. It was also found out that the circular cross-sectional conductors have better properties than the rectangular ones from the same viewpoints.

A large current AC superconductors were fabricated and tested. A strand with more than 20000 NbTi filaments was extruded down to 0.153 mm in diameter to produce filaments of 0.57 µm in diameter. The mixed matrix composed of Cu and CuNi was employed. A final conductor was made of 12 2nd-level sub-cables (6×7 strands) with a mandrel and was compressed on its four sides like a Rutherford type one. Four kinds of conductor were fabricated; one had an FRP mandrel, and the other three had a stainless steel mandrel with various compression rate. They were wound on FRP bobbins to form coils. Three of four coils were successfully operated up to about DC 5 kA.

Large-current-capacity superconducting cables for AC use have been successfully fabricated and tested with regard to AC losses and quench behaviors. The final cables are compacted flat conductors made by triply twisting superconducting composites with NbTi filaments of 0.57 urn in diameter.

The construction program of 40 T-class hybrid magnet is proceeding on the base of a 5-year plan starting from 1988 fiscal year. At the 1st stage we carried out a R & D study on the candidate materials for magnet conductors, such as Nb-tube processed (Nb, Ti)3Sn multifilamentary conductors and Cu-Al203 alloys. The primary design of a 40 T class hybrid magnet with associated facilities were also worked out. The design assumes generation of a back-up field of 15 T (Bmax of 15.7 T) at 4.2 K with a superconducting magnet with a room temperature bore of 400 mm. A water-cooled magnet is designed as a polihelix type one to generate incremental fields up to 25 T in a clear bore of 30 mm with power consumption of about 14 MW.

A D-shaped 12 Tesla superconducting coil with forced cooling Nb 3 Sn superconductor is developed. Cryogenic stability and conduit stress analyses, result of winding test of copper dummy coil, add cooing system for the test coil are presented.

The electronic band structure of a ferromagnetic chromium spinel CuCr2S4 is calculated self-consistently by using the discrete variational X alpha method. The main features of the band structure are: relatively narrow valence bands constructed mainly from the S 3p orbitals lie in the lower energy region; very narrow bands having mainly d character range over the intermediate energy region and a few d bands with only majority spin cross the Fermi level, which corresponds to the p-type metallic conduction observed; true conduction bands composed of Cu and Cr 4s, 4p orbitals lie in the higher energy region. The valency of each ion obtained from the self-consistent calculation is Cu1.3+(Cr1.55+)2(S1.11-)4 and the atomic spin-polarisation is 3.2, -0.32 and -0.27 for Cr, Cu and S, respectively.

The influence of aluminum additions to a Ti-7 at. pet Mo alloy on the phase equilibria was investigated. The microstructures of the alloys, Ti-7 pct Mo-7 pct Al and Ti-7 pct Mo-16 pct Al, were determined by light and electron microscopy. It was found that with increasing aluminum concentration the formation of the metastable w phase was suppressed. In the Ti-7 pct Mo-16 pct Al alloy the β phase decomposed upon quenching by precipitating coherent, ordered particles having a B2 type of crystal structure (β2). At low temperatures the equilibrium phases for this alloy were β + α+ β2, whereas at high temperature (850° to 950°C) the Ti3Al phase was in two-phase equilibrium with the β phase. The four-phase equilibrium which exists at a temperature of about 550°C involves the reaction β + Ti3Al ⇌ α + β2.

The mechanical properties of Ti-7 Mo-7 Al and Ti-7 Mo-16 Al (in at. pct) were correlated to the microstructure. The mechanical properties of the alloy with low aluminum content, consisting of α+ β phases, were dependent on the size of the α particles. Although the α phase is softer than the β phase, the small α particles, upon plastic deformation of the alloy, functioned as typical hard agents in a dispersion-hardened system and the volume fraction of the particles controlled the macroscopic ductility. A rapid strain-hardening behavior of the small α particles seemed to be responsible for this effect. Large α particles behaved like soft, incoherent particles, the volume fraction having little effect on the inherent ductility of the alloy. The two phase (β+ Ti3Al) microstructure of the alloy with high aluminum content resulting from high temperature aging to 900°C exhibited a yield stress of 130 ksi and an elongation to fracture of 5 pct. The ductility of this microstructure was controlled by the volume fraction of the Ti3Al particles inducing homogeneous slip. The favorable ductility properties of the microstructures with low Ti3Al volume fraction were lost if the slip mode was changed from homogeneous slip to planar slip.

The phase diagram of the isopleth section of the Ti-7 at. pct Mo-Al system has been improved and expanded to include alloys up to 25 at. pct aluminum. The mechanical and thermal stability of alloys aged in the two-phase region, β +Ti3Al, was correlated to the microstructure. X-ray rocking-curve studies of the polycrystalline specimens showed that after 2 pct deformation of a Ti-7 Mo-16 Al alloy theβ matrix became preferentially plastically deformed, while the Ti3Al particles functioned as hard particles undergoing little lattice distortions.