Improving the performance of trapped field magnets made of drilled bulk high-temperature superconductors by filling the holes with a soft ferromagnetic material.

The field trapped in a drilled bulk high-temperature superconductor
(HTS) is shown to be enhanced when the holes are filled with a powder
of a soft ferromagnetic material. Characterizations based on Hall
probe mapping and magnetization measurements are used and show an
increase of the trapped magnetic field after impregnation. These
results are examined with the help of a 3D finite element model, where
the ferromagnet material has a simplified, linear, constitutive law in
order to keep a manageable number of mesh nodes. Although such an
approach is a first-order approximation, it already confirms the
experimental observation and indicates a maximum increase of the
magnetic flux of 40 %.