The oxide dispersion strengthened copper (ODS-Cu) was composed to Cu stabilizer in Nb3Sn wires with/without Ta-reinforced filaments to improve the mechanical-electromagnetic property. The wires are 1-mm diameter and heat treated at 650 C for 200 hours. The critical current as a function of the uniaxial tensile strain/stress was explored at 4.2 K, in magnetic fields up to 18 T. The stress/strain sensitivity of the critical current is discussed from a large stress/strain application point of view.

Effect of ODS-Cu Composition for Mechanical-Electromagnetic Property of Bronze-Processed ${\rm Nb}_{3}{\rm Sn}$ Superconducting Wire

We have applied compressive stress perpendicular to YBCO coated tapes, and measured the degradation of critical currents. When the tape was pushed from the silver surface of the tape, the performance of the tape hardly decreases. On the other hand, compressing from the hastelloy face, degradation of the tape occurred. We observed the damage of the tapes by a magneto-optical imaging technique. The observed results were consistent with the degradation data. From those results, we think that it is better not to compress strongly from the hastelloy side.

Characteristics of Compressive Strain and Superconducting Property in YBCO Coated Conductor

We have fabricated two kinds of Nb/sub 3/Sn superconductors having the same diameter; one superconductor is reinforced by center-gathered tantalum (Ta) in a cross-section of the conductor, and the other is reinforced by distributed Ta in the cross-section. We applied compressive force to the conductors, and measured degradation of the conductors. When the conductor's strain due to the compressive force to the conductors was zero, a critical current (I/sub c/) of the distributed Ta conductor was larger than that of the center-gathered Ta conductor. However, an I/sub c/ of the distributed-Ta type conductor rapidly decreased, and when the compressive strain became approximately 5 or 6%, the I/sub c/ of the center-gathered Ta conductor exceeded that of the distributed-Ta type. It was experimentally shown that the center-gathered Ta conductor was more tolerant than the distributed Ta conductor about the compressive strain to the conductor.

Compressive strain and critical current properties of Nb/sub 3/Sn conductors reinforced by center-arranged and distributed Ta

We have been developing tantalum-fiber-reinforced bronze process niobium-tin wires for use in large-scale high field magnets. They are fabricated by conventional drawing. We manufactured two kinds of the wires with different geometries but similar volume ratios. We have investigated their characteristics and have clarified that there are some differences in their superconducting critical current, critical magnetic field, critical temperature, and the influence of their heat-treatment conditions.

Influence of Ta-reinforcement geometry in Nb/sub 3/Sn wires

An Nb 3 Sn-based superconductive wire which, when used in a superconductive magnet, manifests sufficient strength also against force along the radius direction in operating the magnet and reveals little deterioration in properties due to mechanical strain ascribable to the force along the radius direction is provided. An Nb 3 Sn-based superconductive wire comprising a bronze/filament aggregate obtained by placing a lot of niobium (Nb) or niobium alloy filaments in a copper (Cu)-tin (Sn)-based alloy matrix, wherein said niobium or niobium alloy filament constituting the bronze/filament aggregate 3 ′ is a composite filament 5 obtained by combining with a filament reinforcing material having mechanical strength under temperature not more than room temperature after thermal treatment for producing an Nb 3 Sn-based superconductive compound, larger than the mechanical strength of the niobium or niobium alloy.

Nb3Sn-system superconductive wire

We have been developing fiber-reinforced type of niobium-tin superconductor for large scale high field magnets. In this conductor, each niobium-tin filament has a tantalum core. Tantalum is selected as material for the core since it has good ductility with mechanical strength and hence a conventional drawing method can be applied to fabricate a conductor. Stress-strain characteristics and the irreversible strain limits of the conductor with different heat-treatment conditions are measured. Combining these results, discussions about the mechanical properties of the conductor are presented.

Mechanical properties of a niobium-tin superconductor reinforced by tantalum cores

We have been developing fiber-reinforced type of niobium-tin superconductor for a large-scale high field magnet. This conductor has a niobium-tin filament reinforced by a tantalum core of about 20-micrometer diameter. Tantalum is selected as a reinforcing material since it has good ductility with mechanical strength comparable to stainless steel. We have tested this conductor in the form of a small solenoid with the diameter of 50 mm under a backup magnetic field of 15 Tesla. Results of the test showed that it has a uniform superconducting property over a length of 250 meter. Furthermore, we developed another conductor with larger current carrying capacity and tested this conductor in the coil form. Strain measurement of the second coil revealed that the windings behave elastically within the range of operation.

J. Kondoh

Papers

Mechanical properties of a niobium-tin superconductor reinforced by tantalum cores

Influence of Ta-reinforcement geometry in Nb/sub 3/Sn wires

Proofing tests of a fiber-reinforced type of niobium-tin superconductor by small coil experiments

Mechanical Properties of a Superconductor Reinforced by Niobium-Tin