Reinforcing stabilizers for large scale and/or high field superconducting magnets

It is desired to develop a high-strength high-conductivity material for reinforcing composite superconductors which will be employed in large-scale and/or high-field superconducting magnets in emerging large-scale projects such as fusion magnets, SMES magnets, hybrid magnets, and so on. A review of our decade long study of reinforcing stabilizers, and recent results on CuNb composite wires and high-purity Ta wires are reported. Mechanical and electrical properties are reported for CaO crucible melted and drawn CuNb composite wires and for heavily cold worked high-purity Ta wires. Tensile tests at room temperature show a yield stress of about 556 MPa even after annealing at 750°C for 1 h for CuNb composite wires and 0.2% proof stress of about 666 MPa for the Ta wires. Resistivity at 4.2 K is about 0.25 μ ω cm for CuNb wires and about 0.40 μω cm for the Ta wires, respectively at a field of 15 T. It is concluded that the CuNb composite wires, the high-purity Ta wires and the Al₂O₃ dispersion-strengthened copper are suitable as a reinforcing stabilizer for conductors of large-scale and/or high-field superconducting magnets.