Study On High Jc And Low Ac Loss Nbti/Cu5ni Superconducting Wire For Hiaf Magnets In Wst

The High Intensity Heavy Ion Accelerator Facility (HIAF) is a new engineering project proposed by Institute of Modern Physics (IMP) of China. Various types of superconducting wires with the matrix of CuNi alloy for HIAF project were successfully developed by WST. NbTi/Cu5Ni superconducting wires with filaments number of 10800, 12960, 15984, 23760, 36720 and 44064 were designed and fabricated by a double stacking method. In this study, the microstructure and influence of a heat treatment on the critical current density, hysteresis loss and number of breaks of NbTi/Cu5Ni superconducting wire are investigated. It is demonstrated that when the number of heat treatments increases from 3 to 5, the critical current density increases from 2324 to 2699 A/mm(2) at 5T&4.2K for a 10800-filament wire. However, the number of breaks per one billet increases from 0 to 3. The maximum and minimum piece length is 3500 and 1000 m, respectively. The Nb barrier fracture results in the formation of the Ti-Cu compound between NbTi filaments and Copper during intermediate heat treatment. By reducing the Cu/Sc of sub-elements and improving the Cu shell thickness of the final billet, the deformation of outer filament is relatively favorable, which can enhance the critical current density and reduce hysteresis loss. The critical current density of six designed wires is between 2600 and 2700 A/mm2 and 'n' value is between 35 and 48 at 5T&4.2K, indicating a high filament quality and that no filament breakage occurs in the wire. The Cu5Ni alloy is regarded as the inter-filament matrix to reduce inter-filament coupling currents loss. When the filament number increases from 10800 to 44064 and the diameter of NbTi filament reduces from 4.5 to 2.5 mu m, the hysteresis losses reduce from 38.5 to 26.2 mJ/cm(3) at +/- 3T. The average piece length of six designed wires is more than 2000 m, revealing the ability of mass production for WST. After 5 years investigations WST have developed several designs and the fabrication technology of this type of wire and can completely satisfy the requirements of HIAF magnets.