Fabrication and transport properties of MgB2 mono-core wire and solenoid coil

Round 100 m long class MgB₂ mono-core wires with Fe/Cu composite sheaths were successfully fabricated using an in situ PIT method. The J_c of the round MgB₂/(Fe/Cu) wires reached 380 A/mm² at 4.2 K and 6 T, and exceeded 2500 A/mm² at 3 T. High areal reduction of the MgB₂ core was found to be effective in improving the transport properties of the MgB₂ wires. Using a 58 m long MgB₂/(Fe/Cu) wire, we made a solenoid coil with 495 turns and tested it in liquid helium. The dimensions of the MgB₂ coil were 30 mm in inner diameter, 48 mm in outer diameter, and 50 mm in height. The I_c of the coil reached 214 A, which corresponds to a J_coil=238 A/mm² and a core-J_c=1420 A/mm². The coil generated a magnetic field at a center of B_o=2.05 T and a maximum magnetic field of B_m=2.17 T.