Transport Properties of CuNb/Nb₃Sn Rutherford Coils With Various Diameters

Our group has been developing an Nb-rod-processed CuNb-reinforced Nb₃Sn Rutherford cable for developments in high-field superconducting magnets, such as a 25-T cryogen-free superconducting magnet. The Rutherford cable has good mechanical, electrical, and superconducting properties in high fields. In this paper, we investigated the influence of winding coil diameters on the transport properties of the Rutherford cable for the coil application wound with a react-and-wind method. We prepared two Rutherford coils with diameters of 110 mm (0.2% pure bending strain) and 70 mm (0.6% pure bending strain) with 0.7% prebending treatment in order to measure the critical current at various temperatures in fields up to 18 T. We found that the Rutherford coil with a diameter of 110 mm has good transport properties. The critical current of the Rutherford coil with a diameter of 70 mm exhibited a deterioration of about 14% in comparison to the coil having a diameter of 110 mm. Although the tensile strain dependence of the critical current (I_c) suggests a large deterioration for the 0.6% pure bent coil, the Rutherford coil can keep the high I_c under a large pure bending strain.