Precursor wire for Nb
Problem There is proposed an innovative cross-sectional structure, with an idea contrary to the conventional one, utilizing the non-reactivity between Cu and Ta (or between Ag and Nb, Ta) in a high-temperature short-time heat treatment, thus achieving (1) the suppression of the low magnetic-field instability, (2) excellent wire drawability of a precursor wire, and (3) the reduction of the cost required for the incorporation of a stabilizer. Means for Resolution There is proposed a structure having an assembly of a plurality of single wires, wherein the assembly is covered with an outer cover (skin) formed from Nb or Ta, wherein each of the single wires has an Nb/Al composite filament region which is formed from a composite of Nb and Al mixed in an Nb:Al molar ratio of 3:1, and which is covered with a partition formed from Nb or Ta, and further covered with an interfilamentary barrier formed from Cu or Ag disposed around the partition.
1. A precursor wire for producing an Nb 3 Al superconducting wire by rapid-heating, quenching and transformation processes, comprising an assembly of a plurality of single wires, the assembly being covered with an outer cover (skin) formed from Nb or Ta,
wherein each of the single wires comprises an Nb/Al composite filament region which is formed from a composite of Nb and Al mixed in an Nb:Al molar ratio of 3:1, an interfilamentary barrier formed from Cu or Ag covered on the outside of the Nb/Al composite filament region for effectively electromagnetic decoupling of superconducting filaments, and a partition formed from Nb or Ta provided between the Nb/Al composite filament region and the interfilamentary barrier for preventing the interfilamentary barrier from reacting with the Nb/Al composite filament region to form a non-superconducting compound,
wherein the volume fraction of Cu or Ag in the single wire is 7 to 25%, and
wherein, when Cu is used as the interfilamentary barrier, Ta film having a thickness of 5 μm or more is used as the partition, and, when Ag is used as the interfilamentary barrier, Nb or Ta film having a thickness of 1 μm or more is used as the partition.
2. The precursor wire for producing Nb 3 Al superconducting wire according to claim 1 , wherein internal stabilizer filaments each formed from Cu or Ag and covered with an internal-stabilizer-filament-covering-layer formed from Nb or Ta are disposed inside the assembly.
3. The precursor wire for producing Nb 3 Al superconducting wire according to claim 1 , wherein dummy filaments each formed from Nb or Ta and covered with a dummy filament covering layer formed from Cu or Ag are disposed inside the assembly.
4. The precursor wire for producing Nb 3 Al superconducting wire according to claim 1 , wherein the assembly comprises Cu, and wherein the assembly is covered with the outer cover (skin) comprising Ta.
5. The precursor wire for producing Nb 3 Al superconducting wire according to claim 1 , wherein the assembly comprises Ag, and wherein the assembly is covered with the outer cover (skin) comprising Nb or Ta.
6. An Nb 3 Al superconducting wire which is obtained from the precursor wire for the Nb 3 Al superconducting wire according to claim 1 , wherein the Nb/Al composite filament regions have been converted to the Nb 3 Al filaments.
7. A method for producing an Nb 3 Al superconducting wire, comprising: subjecting the precursor wire for the Nb 3 Al superconducting wire according to claim 1 to heat treatment at 1,900° C. or higher for 5 seconds or less; quenching the resultant precursor wire to 500° C. or lower; and subjecting the quenched wire to additional heat treatment at 700 to 900° C.