Transport properties of CuNb reinforced Nb₃Sn Rutherford coils in high fields

Nb₃Sn Rutherford cables have been investigated for the development of a 25-T cryogen-free superconducting magnet. We developed Rutherford cables composed of 16 Nb-rodprocessed CuNb-reinforced Nb₃Sn (CuNb/Nb₃Sn) strands with an 0.8-mm diameter. In this paper, the transport and mechanical properties of the epoxy impregnated multilayer coil of the (CuNb/Nb₃Sn) Rutherford cable were investigated in high magnetic fields. The coil reached the maximum transport current of 1655 A at 4.2 K and 13.5 T after four times of training quenches. The electromagnetic stresses at the maximum transport current were 240 MPa at an inner surface of the coil and 210 MPa at an outer surface of the coil. The hoop strain of 0.2% for the coil was measured, which was applied at the outer surface of the coil. The strain value was the same as the calculated result using Wilson's equation and stress-strain curve of the strand.