Adrian Mark Thomas

Pulsed Magnetic Field Assisted Technique for Joining

The commercial availability of long lengths of MgB2 conductor with an increasingly attractive price-to-performance ratio encourages its use in cryogen-free magnetic resonance imaging magnets. For such a magnet operating in persistent mode, connections between MgB2 wires must be completely superconducting to ensure long-term magnetic field stability. A new electromagnetically assisted technique for joining MgB2 conductors is proposed. An electrically conducting tube is electromagnetically formed around the wires to provide mechanical coupling. Mg + 2B powder is placed inside this tube between the wire ends with exposed MgB2 cores. Pulsed magnetic field compression of the tube densifies the joint powder, which is also redistributed into better contact with wire cores, and forms the tube to the shape of the joined wires. Cu powder has also been added into the Mg + 2B joint powder to minimize the reactive diffusion between Mg and Cu components. Finite element modeling of the deformation process will be presented, along with critical current measurements performed on a joint and on the individual wire for comparison. The applicability of this method for joining wires in reacted and unreacted form for magnet applications will be discussed.

\hbox{MgB}_{2}

Recently, 3T MRI system has been one of the fastest growing segments of the MRI clinical diagnoses. In order to lower the 3T MRI cost and allow it to be more widely applied, especially in developing country like China, this paper presents a conceptual design of a 3T superconducting magnet with a non-thrust face integrated former for a whole body MRI system. The concept is an 8-coil active shielded magnet design with the minimized 82 cm standard warm bore size. The operating current is 480 A and the full field is 2.9T. The integrated former was designed to further minimize the coil internal diameter and reduce the superconducting wire length. Unlike traditional formers, there are no coil slots on the former for the coil supporting and positioning to reduce former manufacturing cost. The coils are wound and cast on a detachable mould tooling, and then bonded onto the outer surface of the integrated former. At 4.2 K, the coils remain bonded to the surface of the former; this prevents slight relative movement between the coil and the former in the coil energizing process. This coil-former structure can reduce the quench rate during the magnet ramping process to save liquid Helium and the build quality cost.