Yoshiji Hotta

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.

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.

Evaluation tests for large scale multi-filamentary Nb 3 Sn superconductors

Six different configurations for multifilamentary Nb 3 Sn conductors for large scale magnets with high magnetic fields were developed and tested. These conductors, which could carry approximately 1kA at 13T, were cryogenically stable, reinforced superconductors 4.5mm × 10mm in size. Critical currents, stability and the effects of stress were measured in short sample tests. Conductor stability was related to barrier configuration. At stresses above 250-800 MPa the critical current was significantly degraded, with the magnitude of the reduction depending on reinforcement techniques and the construction of the conductor. A monolithic conductor which was composed of filament groups surrounded by barriers, each of which was composed of 331 filaments, and which was about 30% stainless steel by total volume was found to be suitable for large scale magnets with high magnetic fields.

Development of aluminum-stabilized superconducting coil

Aluminum-stabilized NbTi superconducting wires have been developed for the purpose of increasing the stability margin of a close-packed superconducting coil with high current density. The effects of high purity aluminum stabilizer on the stability margin and the normal propagation velocity were investigated in the coil operation. It was verified that the coil stability margin is significantly improved by using the aluminum-stabilized superconducting wire. The experimental data of the coil stability margin are in good agreement with the calculated results by one-dimensional transient computer simulation analysis. >

Development of kA-Class ac superconducting wires

Abstract We have developed large-current-carrying superconducting wires for the application of superconductivity for fast pulsed magnets and ac power devices such as SMES, superconducting rotating machines and transformers. Critical current and ac losses measurements under 50 Hz operation have been performed. Results show that the superconducting wires have ac transport current more than 1000 A rms at 50 Hz with 2 T dc backup magnetic field, and relatively low ac losses. The result also shows that the mechanical rigidity should be carefully concerned togetther with the reduction of the losses in the development of ac superconducting wires.

(Nb, Ti)3Sn forced-flow-cooled superconductor

Abstract A low ac loss (Nb, Ti) 3 Sn bundle-type forced-flow-cooled multifilamentary superconductor was developed for application as a toroidal field coil (dc operation) and a poloidal field coil (pulsed operation) of the fusion reactor. The diameter of the filament was reduced to 1.42 μm (the finest possible in the present technical stage) and filaments in the bronze matrix and the stabilizing copper were segmented by the high resistive CuNi layer and Nb barriers for the reduction of ac losses. The ac losses of a superconducting strand measured by an improved boil-off method are lower than for an ac superconducting (NbTi/Cu/CuNi) wire. A small forced-flow-cooled superconducting coil manufactured with this conductor (rated current I d = 2.5 kA, B max = 10 T) showed a high stability margin in dc operation. Repeated pulse operation to the rated current with a high sweeping rate of 13 kA/s (0.85 T/s) was possible without quench in a backup field of 10 T.

DEVELOPMENT OF 10T-(NbTi)3Sn FORCED FLOW COOLED SUPERCONDUCTING COIL

10T-2.5kA (NbTi)3Sn cable-in-conduit type superconducting conductors varying a void fraction in cable space 39.9% and 46.6% were developed and two small one-layer solenoid coils (10 turns) were manufactured by a wind & react method. Several verification tests were performed under the condition of 10T uniform back-up field and mass flow rate of the supercritical helium ·0g/s ~4g/s at 4.2K, 0.45MPa. It was found that the stability margins of these coils were large enough to apply for the fusion magnet and the normal propagation velocity was about 4m/s at the rated current. The friction factors of these conductors were little larger than those reported in the other data of cable-in-conduit type conductors.