Mechanical and superconducting properties of Nb₃Sn wires with Nb-rod-processed CuNb reinforcement

Abstract

New Nb-rod-processed CuNb reinforced Nb 3 Sn superconducting wires have been developed for large high field magnet applications. The critical current, I c , mechanical properties and resistivity are investigated. The residual strain and irreversible strain are found to be 0.35% and 0.77%, respectively. We found that the Nb-rod-processed wire has a large strain sensitivity to I c . However, the wire has good mechanical properties, having a 0.2% proof stress of 280 MPa and a Young's modulus of 150 GPa. This means that the stress sensitivity of the I c for the wire is small. These results show that the Nb-rod-processed wire is suitable as a strand of Rutherford cable for a high field superconducting magnet.

High temperature superconductors for commercial magnets

“…The possibility to reduce the size compared to LTS systems is a result of the fact that many HTS conductors have been extensively optimized for mechanical strength, whereas this is, with some exceptions (e.g. [64]), much less the case for LTS. This will be discussed in more detail in section 5.5.…”

“…This is usually not the case for LTS, which mostly have a copper matrix. A recent exception is CuNb-reinforced Nb 3 Sn that is used in the Tohoku University 25 T cryogen-free user magnet [58,64]. As a result of the higher mechanical strength of HTS, operating current-densities can be higher before the stress-limitations are reached, resulting in more compact magnet systems (see, e.g [63]).…”

Performance of a 14-T CuNb/Nb3Sn Rutherford coil with a 300 mm wide cold bore

“…The Nb 3 Sn Rutherford cables must overcome very large electromagnetic stress in order to operate the 25T-CSM [1]. We used the Nb-rod-processed CuNb reinforced Nb 3 Sn as a strand of the Rutherford cable for the 25T-CSM [9][10][11][12]. In addition, we found that the superconducting and mechanical properties of the Rutherford cable were enhanced by a prebending treatment after a heat treatment at 670 °C for 96 h [12].…”

“…Previously, we developed a new high-strength bronze route Nb 3 Sn strand for a Rutherford cable using a Nb-rodprocessed CuNb alloy for a reinforcement material (CuNb/ Nb 3 Sn). The CuNb/Nb 3 Sn exhibits good mechanical, superconducting, and electrical properties in high magnetic fields [9][10][11][12]. The Young's modulus and 0.2% proof stress of the CuNb/Nb 3 Sn strand are 150 GPa and 280 MPa, respectively.…”

“…The residual resistance ratio of the strand is 137. In addition, prebending treatment enhances the superconducting and mechanical properties [9].…”