AC Loss Measurements on Multi-Filamentary $\hbox {MgB}_{2}$ Wires With Non-Magnetic Sheath Materials

The MgB₂ superconductor is an attractive choice for many high-current dc applications, particularly for its low cost compared with, e.g., YBCO, and the higher operating temperature than the low-temperature superconductors. To extend the operating range to include also ac applications, the ac losses need to be determined and a path towards a low-loss conductor needs to be established and verified. To accomplish this development, systematic and reliable measurements of the losses are essential. In this paper, we present ac loss measurement results on nontwisted MgB₂ wires with titanium and copper-nickel matrices. 50 hertz ac losses were measured calorimetrically in applied magnetic fields, with transport currents, and with combinations of both. The temperature range was between 25 K and T_c, the magnetic field was varied up to 300 mT, and the transport current up to 113 A. The measurement results are used as a basis to discuss the necessary ac loss reduction steps in MgB₂ superconductors.