MgB
An MgB 2 superconducting wire includes a core containing MgB 2 and a metal sheath which surrounds the core. The core includes at least a first MgB 2 core positioned on the center side, and a second MgB 2 core positioned outside the first MgB 2 core, and the density of the second MgB 2 core is lower than the density of the first MgB 2 core.
1. An MgB 2 superconducting wire comprising a core containing MgB 2 and a metal sheath which surrounds the core, wherein
the core comprises at least a first MgB 2 core positioned on the center side, and a second MgB 2 core positioned outside the first MgB 2 core, and the density of the second MgB 2 core is lower than the density of the first MgB 2 core, and
the density of the second MgB 2 is less than 70% of the true density of MgB 2 ,
there are voids which extend in the longitudinal direction of the MgB 2 superconducting wire, in the first MgB 2 core, and
the void in the first MgB 2 core has the same shape as a void present in the second MgB 2 core, and the ratio of the void in the first MgB 2 core is smaller than the ratio of the void in the second MgB 2 core.
2. The MgB 2 superconducting wire according to claim 1 , wherein the density of the first MgB 2 core is 70% or more of the true density of MgB 2 (2.62 g/cm).
3. The MgB 2 superconducting wire according to claim 1 , wherein the cross sectional area of the first MgB 2 core is 50% or more of the whole cross sectional area of the core.
4. The MgB 2 superconducting wire according to claim 1 , wherein the ratio of the void in the first MgB 2 core is 20% or less.
5. The MgB 2 superconducting wire according to claim 1 , wherein the MgB 2 superconducting wire is used as a superconducting cable or a superconducting magnet.