Nb

1. A precursor for fabricating a Nb 3 Sn superconducting wire, the precursor being used for fabricating the Nb 3 Sn superconducting wire by an internal Sn process, the precursor comprising:

one or a plurality of stabilizing copper portions collectively disposed in the center, each stabilizing copper portion being provided with a diffusion barrier layer in the periphery thereof; and

a superconducting matrix portion disposed so as to surround the one or the plurality of stabilizing copper portions, the superconducting matrix portion including a Nb or Nb-based alloy core and a Sn or Sn-based alloy core embedded in a Cu or Cu-based alloy matrix,

wherein the superconducting matrix portion includes an aggregate of precursor elements each including a plurality of Nb or Nb-based alloy cores and at least one Sn or Sn-based alloy core, the aggregate being embedded in a Cu or Cu-based alloy matrix, and

wherein, apart from the diffusion barrier layer, a diffusion barrier layer made of Nb or an Nb-based alloy is provided for each precursor element.

2. The precursor for fabricating a Nb 3 Sn superconducting wire according to claim 1 , wherein the diffusion barrier layer provided for each precursor element has a thickness that is equal to or smaller than the diameter of the Nb or Nb-based alloy core.

3. The precursor for fabricating a Nb 3 Sn superconducting wire according to claim 1 , wherein a Sn or Sn-based alloy core is disposed in the periphery of the diffusion barrier layer provided for each precursor element.