Construction and Persistent-Mode Operation of MgB₂ Coils in the Range 10–15 K for a 0.5-T/240-mm Cold Bore MRI Magnet

This paper presents construction and persistentmode operation results of MgB2coils for a 0.5-T/240-mm cold bore MRI magnet, wind-and-react with monofilament MgB2wire at the MIT Francis Bitter Magnet Laboratory. The magnet, of respective inner and outer diameters of 276 and 290 mm and a total height of 460 mm, has center field of 0.5 T and current density of !! kA/cm2. To limit the continuous length of Hyper Tech supplied MgB2monofilament wire to ≤ 300 m, the magnet was divided into eight series-connected coils, each equipped with a persistent current switch and a superconducting joint. We have manufactured three coil modules. Before being tested as an assembly, each coil was tested individually to ensure its capacity to carry 100-A superconducting current in the range of !0-!5 K. The three coils were then assembled, connected in series, and operated as a 3-coil assembly in persistent mode at nearly !00 A in the range of 10-15 K. We present results that include: 1) construction details; 2) component performances; and 3) a 3-coil assembly performance.