MgB₂ for MRI Magnets: Test Coils and Superconducting Joints Results

Among key design and operation issues for MgB₂ relevant to MRI magnets are: uniformity of current-carrying capacity over long lengths (>2 km) of wire; and reliability of a splicing technique. This paper presents experimental results of current-carrying capacities of a small test coil and joints, both made from MgB₂ round wires, multifilament and monofilament (mono), manufactured by Hyper Tech Research, Inc. The test coils were wound with 95-m long unreacted, C (carbon)-doped MgB₂ multifilament wire, sintered at 700°C for 90 min. The critical currents were measured in the 4.2 K-15 K and 0 T-5 T ranges. We have modified our original splicing technique, proven successful with unreacted, un-doped MgB₂ multifilament wire sintered at 570°C, and applied it to splice both un-doped and C-doped mono wires sintered at 700°C. Most consistently good results were obtained using the un-doped mono wires. Also presented are results of a small joint-coil-PCS assembly of mono wire, operated in persistent mode at 50 A at >10 K.