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This study is a contribution to the development of technology for an MgB 2 -based, cryogen-free, superconducting magnet for an MRI system. Specifically, we aim to demonstrate that a react and wind coil can be made using high performance in-situ route MgB 2 conductor, and that the conductor could be operated in conduction mode with low levels of temperature gradient. In this work, an MgB 2 conductor was used for the winding of a sub-size, MRI-like coil segment. The MgB 2 coil was wound on a 457 mm ID 101 OFE copper former using a react-and-wind approach. The total length of conductor used was 330 m. The coil was epoxy impregnated and then instrumented for low temperature testing. After the initial cool down (conduction cooling) the coil I c was measured as a function of temperature (15-30 K), and an I c of 200 A at 15 K was measured.

Among key design and operation issues for MgB 2 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 MgB 2 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 MgB 2 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 MgB 2 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.

Aiming to demonstrate feasibility and practicality of a low cost superconducting MRI magnet system targeted for use in small hospitals, rural communities and underdeveloped countries, MIT-Francis Bitter Magnet Laboratory has developed a 0.6 T/650 mm room temperature bore demonstration coil wound with multifilament MgB 2 conductor and cooled via an innovative cryogenic design/operation. The coil is to be maintained cold by solid nitrogen kept in the solid state by a cryocooler. In the event of a power failure the cryocooler is automatically thermally decoupled from the system. In this paper we present details of the MgB2 conductor, winding process, and preliminary theoretical analysis of the current-carrying performance of the conductively cooled coils in zero background field and over the 10-30 K temperature range.