Magnetic shielding properties of a superconducting hollow cylinder: Influence of a vertical or a horizontal slit

The magnetic shielding properties under both axial and transverse DC magnetic fields are measured at the liquid nitrogen temperature (77 K) on Bi-2212 hollow cylinders obtained by Melt Cast Process. The characterized samples are cut by a slit along either a vertical (parallel to the cylinder axis) or a horizontal (perpendicular to the cylinder axis) plane. The sample with the vertical slit is subjected to a transverse magnetic field whose the direction is varied between 0° and 90° with respect to the normal of the slit plane. The measurements show that there is no influence of the presence of the slit on the magnetic shielding properties for a transverse magnetic field applied perpendicular to the slit plane but a strong reduction of the magnetic shielding efficiency when the angle between the applied transverse magnetic field and the normal to the slit plane exceeds 15°. Numerical modelling using the Finite Elements Method on short-length hollow cylinder allows us to understand how the superconducting currents flow in a slit cylinder depending on the magnetic field orientation. A second sample is cut horizontally by a median plane and is characterized in axial magnetic field configuration. Measurements are carried out along the axis of the cylinder for several slit thicknesses.