Drilled bulk high-temperature superconductors: enhancing the trapped magnetic flux by filling the holes with a ferromagnetic powder

Filling the holes of a drilled bulk high-temperature superconductor (HTS)
with a ferromagnetic powder is shown to enhance its trapping properties. We
use experimental techniques (Hall probe mapping techniques and magnetization
measurements) to characterize the magnetic properties of drilled samples
filled with a soft ferromagnetic powder. The analysis is completed by a
numerical model based on a 3D finite-element method that involves a
conductivity in the form of a power law for the superconducting material,
and a constant permeability for the ferromagnetic material. Numerical
results confirm the experimental observations, and, in particular, they
support the increase of trapped flux after impregnation (max. 40%) that is
observed with Hall probe mappings.