MgB2 for MRI applications: dual sintering induced performance variations in in situ and IMD processed MgB2 conductors

Abstract

Magnesium diboride (MgB₂) is known to have good potential to be used in a commercial liquid helium-free magnetic resonance imaging (MRI) magnet. The magnet is expected to be fabricated using reacted MgB₂ conductors to minimize modifications in the existing magnet production technologies and operated in the persistent mode by forming a closed-loop using superconducting joints. The superconducting joints of the reacted MgB₂ conductors are typically formed by placing unreacted magnesium and boron powders in between them followed by sintering. During this process, the MgB₂ conductors will inevitably experience dual sintering in the vicinity of the superconducting joints. However, the effects of dual sintering on the performance of MgB₂ conductors are still unknown. Therefore, herein, we dual sintered commercially available multifilament in situ and laboratory-made monofilament internal magnesium diffusion (IMD) processed MgB₂ conductors (un-doped and C-doped) and evaluated their transport performance, microstructure, lattice parameters, and critical temperature in detail. In the IMD processed wires, the C-doped boron powder was found to promote a better diffusion of magnesium compared with the un-doped boron powder. Under typical dual sintering conditions, surprisingly, the C-doped in situ wire showed a simultaneous improvement in the engineering critical current density and n-value in different magnetic fields at 4.2 K and 20 K. On the other hand, the remaining conductors showed a strong dual sintering induced transport performance variation. Our findings provide insights into MgB₂ conductors' performance after dual sintering for their further development towards MRI applications.