Superconducting materials must be wrapped or buried in ordinary good conductors to provide a low impedance paribus at certain line segments that suddenly turn into normal. In addition, cladding is important in preventing magnetic field lines from jumping forward. In other words, appropriate basic materials must be used in order to reduce loss and improve stability. The choice of the matrix material depends on conflicting requirements. The theory of Wilson and his colleagues shows that a substrate with high conductivity allows the use of thinner wires, but its multi-strand cables must be twisted more tightly. According to The Germans, the main reason for choosing high conductivity oxygen-free copper as the matrix material of the superconducting material NbTi alloy is that when the superconducting state is disturbed by the local temperature rise, the transport current can be moved into the matrix, so that the joule heat can be kept at a sufficiently small degree. It has been pointed out, however, that copper with good stabilization has not been able to adequately limit the induced current.
Fabrication and editing of practical NbTi alloy superconductor. Alloy smelting. The optimum alloy ratio contains T in 46% ~ 50%(mass percentage). NbTi alloy bar processing, high uniformity of NbTi bar in addition to uniform composition, there are mechanical properties of uniformity.
Coating stabilized materials, so that hundreds of thousands of NbTi filaments are buried in highly conductive non-oxygenated copper or high purity aluminum, which ACTS as stabilization, to prevent heat loss or provide current bypass. Residual resistance ratio (RRR) is often used to describe the quality of stabilized materials. RRR refers to the ratio of the resistivity at room temperature 293K divided by the resistivity at low temperature (4.2K). Normally, superconducting magnets require RRR ratio of stabilized materials to be 30 or above.
The package covers the blocking material. Nb is a widely used barrier layer material, which is designed to avoid the formation of TiCu4 and other intermetallic compounds between NbTi alloy and Cu matrix, and to prevent the cable from breaking and significantly reducing the critical current density (Jc).
