Naofumi Tada

Aluminum-stabilized superconductor and superconducting coil, and method of manufacturing the superconductor

Disclosed is a superconductor which has an aluminum area at the center of the cross section of the superconductor and a copper-covered multifilamentary NbTi composite conductor at the periphery parts of the cross section formed around the aluminum area, wherein the cross-sectional area ratio of (Cu+Al)/NbTi is in the range of 0.5 to 3.0 and the cross-sectional area ratio of Al/Cu is in the range of 0.05 to 0.5.. The superconductor is provided by a method comprising a first step of providing a superconductor-copper composite hollow body in which copper films are applied around the superconductors, a second step of area reducing the composite hollow body, a third step of heat treating the body, a fourth step of inserting an aluminum body into the hollow of the hollow body, a fifth step of subjecting the body to working such as drawing, a sixth step of subjecting the body to working such as twisting, forming or the like, with an additional area reduction being carried out, if necessary, subsequent to the third step. A superconducting coil is made using the superconductor, and the coil is used for a magnetically levitated vehicle or a nuclear magnetic resonance apparatus.

Optimization of critical currents in composite-processed multifilamentary Nb 3 Sn conductors with Nb-Ti alloy cores

Multifilamentary Nb 3 Sn conductors with Nb-(1,2,3, 5at%) Ti alloy cores were successfully fabricated, and the relationships among the amounts of titanium addition to the core, core sizes, heat treatment conditions ,Nb 3 Sn grain structure and the superconducting properties have been studied. The multifilamentary Nb-3Ti/ Cu-7.5Sn conductor shows the highest overall critical current density J c (overall) at 16 T for all the core sizes of 17 μm-diam, 10 μm-diam and 7.5 μm-diam, after the optimum heat treatment. The optimum heat treatment condition for the multifilamentary Nb-3Ti/Cu-7.5Sn conductor varies slightly with core diameter. The J c ( overall) of multifilamentary Nb-3Ti/Cu-7.5Sn conductor with 10 μm-diam 6,289-cores heat treated at 700°C for 200 hr exceeds 2.5×104A/cm2at 16 T. The amount of residual tin in the Cu-Sn matrix of the multifilamentary Nb-Ti/Cu-7.5Sn conductor after heat treatment decreases with increasing titanium content in the core and decreasing core diameter. The multifilamentary Nb-3Ti/Cu-7.5Sn conductor showed appreciably improved uniaxial strain dependence of critical current I c at 14.5 T, as compared to that for a typical multifilamentary Nb 3 Sn conductor. The multifilamentary Nb-3Ti/Cu- 7.5Sn conductor developed in this study makes feasible to generate a magnetic field of 16 T.

Generation of magnetic fields over 20 T using a newly developed superconducting magnet system

In February 1992, a newly developed superconducting magnet system at the National Research Institute for Metals accomplished generation of a magnetic field of 20.3 T in its clear bore of 44 mm in diameter. The authors give an outline of the magnet system together with the operation results. The required time to cool down from 4.2 K to 1.8 K was about 4 h. The operations carried out at 1.8 K proved that saturated superfluid helium can be applied as coolant for large scale superconducting magnets because no problems, such as a discharge in the coils, were observed even when quenches occurred. This magnet system may be useful for testing coils of new high-field superconductors.<<ETX>>

Manufacturing of titanium-bronze processed multifilamentary Nb 3 Sn conductors

It has been revealed that small amount of titanium addition to the bronze matrix is most effective for improving the high-field current-carrying capacities of bronze-processed multifilamentary Nb 3 Sn conductor. Multifilamentary Nb/Cu-7.5 at %Sn-0.4 at %Ti round wires with 4-5 μm-diam 31×331-cores fabricated through drawing process only showed the overall critical current density J c (overall) over 3.5 × 104A/cm2at 15 T after the heat treatment at 690°c for 200 hr. It was also shown that the critical current anisotropy became larger with increasing aspect ratio of the rectangular shaped multifilamentary Nb/Cu-7. 5Sn-0.4Ti conductors. Rectangular shaped 5 μm-diam 31 × 361-core Nb/Cu-7.5Sn- 0.45Ti conductors prepared through double extrusions showed about the same tendencies in the aspect ratio dependence of I c ( H_{\parallel}) as those prepared through drawing process only, after the heat treatment at 690°C for 200 hr. 9.5 mm wide and 1.8 mm thick Nb/Cu-7.5Sn-0.4Ti conductors with 5 μm-diam 349 × 361-cores have been successfully fabricated in full production scale through three steps hydrostatic extrusion process. These rectangular shaped practical multifilamentary Ti bronze Nb 3 Sn conductors make feasible to generate a central magnetic field over 16 T in the 190 mm winding inner diameter intermediate coil of the 18 T superconducting magnet at NRIM.

Improved multifilamentary Nb3Sn conductors produced by the titanium-bronze process

The effects of a titanium addition to the bronze matrix of superconducting Nb3Sn wires have been investigated. The titanium addition to the matrix remarkably increases the Nb3Sn growth rate and the high-field, critical current density of the wire. An overall critical-current density of 3.8 × 104 A/cm2 at 15 T has been obtained for the multifilamentary Nb/Cu−7.5 at % Sn−0.4 at.% Ti wire with 4.7 μm-diameter 31 × 331 cores. The anisotropy in the critical current with respect to the field direction becomes larger with increasing aspect ratio of the rectangular-shaped multifilamentary wires. A 9.5 mm wide and 1.8 mm thick Nb/Cu-7.5Sn-0.4Ti conductor with 5 μ m-diameter 349 × 361 = 125 989 cores has been successfully fabricated on an industrial scale. This conductor carries a superconducting current of over 1300 A at 16.5 T. The newly developed Ti-bronze Nb3Sn conductor makes it feasible to generate a field of ~15 T in a large diameter bore.

Development of a 20 T class superconducting magnet with large bore

A 20 T class superconducting magnet has been constructed at the National Research Institute for Metals in Japan. The two outermost of the four coils have been operated at 4.2 K. Before operating all coils at 1.8 K, in saturated superfluid helium, breakdown voltages within the coils were measured. With an inner coil of preliminary design, the system should generate 20.4 T in a 44 mm free bore. >

Development of superconductors for a 70 MW class superconducting generator

Since 1988 a project has been underway in Japan in which superconducting generators for utility applications are being developed. The aim of the project is the development of a 200-MW-class superconducting pilot generator. During development work, of 70-MW-class superconducting, model generators are being run in order to clarify the problems in manufacturing and operating the pilot generator. The design of the model generator and the development of the components, especially the superconductors for the generator are discussed. Details of the development of the superconductor installed in the rotor are described.

High-Field Current-Carrying Capacities of ‘Titanium Bronze’ Processed Multifilamentary Nb3Sn Conductors with Pure and Alloy Cores

It is required for multifilamentary Nb3Sn conductors to have more improved current-carrying capacities in high magnetic fields to meet the demands for the 1st phase target of making a 190 mm-diam bore coil operating at 14 T in the high-field superconducting magnet project at NRIM and also to meet the near future demands for the applications such as fusion reactor magnets and high energy particle accelerators. We have shown that the composite-processed multifilamentary Nb3Sn conductors with small amount of titanium addition to the core are feasible for these requirements. It is revealed that the multifilamentary Nb-3at%Ti/Cu-7.5at%Sn conductors heat treated at 700°C for 200 hr and 750°C for 100 hr show overall critical current densities Jc(overall)’s over 2.5 × 104 A/cm2 at 16 T and 1.0 × 104 A/cm2 at 20 T, respectively.1 The uniaxial strain sensitivity of critical current Ic for the multifilamentary Nb-3Ti/Cu-7.5Sn composite wire is shown to be much reduced as compared to that for pure multifilamentary Nb3Sn wires.2 Recently, it has been reported that the small amount of titanium addition to the bronze matrix also significantly increases the growth rate and the critical current density Jc in high magnetic fields of the Nb3Sn layer for the composite-processed single-core Nb3Sn wires in the same way as that to the niobium core does.3

Electrical resistivity change in Cu and AI stabilizer materials for superconducting magnet after low-temperature neutron irradiation

Abstract The change of electrical resistivity in magnetic field has been studied at 4.2 K in both copper and aluminum irradiated by fast neutrons at 5 K, together with the isochronal annealing behaviors and the effects of the irradiation-anneal cycles (cyclic irradiation). The increasing rate of the resistivity by the irradiation in aluminum is about three times as large as that in copper in zero magnetic field. The rates in the high purity copper with R 294k R 4,2k (RRR) of 1400 and aluminum with RRR of 1500 increase remarkably with an increase in applied magnetic field to the low irradiation doses, while those in the impure copper with RRR of 280 and 300 are independent of magnetic field. The radiation-induced resistivity in copper cannot be recovered even by annealing at 300 K. and the retained resistivity decreases in the cold-worked samples. The retained resistivity is accumulated by the cyclic irradiation. The radiation-induced resistivity of aluminum is completely annihilated by the annealing at 300 K.

Development of multifilamentary Nb 3 Sn conductor for fusion research

A 10kA/13T Nb 3 Sn conductor, which is intended for use in fusion magnets, has been developed. The conductor consists of multifilamentary Nb 3 Sn conductor monoliths with a copper stabilizer and stainless steel reinforcement monoliths laminated with copper. The conductor design is based on the results of experiments with model conductors (1kA/10T and 0.1kA/7T), which show that a conductor can be reinforced effectively and that reinforcement can reduce eddy current losses in a conductor.