Trapped magnetic field distribution above a superconducting linear Halbach array

A compact system generating a large gradient of the magnetic flux density is often required in applications involving a magnetic force. One well-documented way to compactly generate such magnetic gradients is to assemble permanent magnets in a Halbach array. However, the saturation magnetization of the magnets involved in the array is a fundamental limitation impeding the performance of this configuration. The use of trapped field superconducting magnets instead of permanent magnets in a Halbach array could potentially allow the generation of larger field gradients as they do not suffer from the same limitation.
In this context, the assembly of cuboid bulk, large grain melt-textured YBCO superconductors (~14x14x14 mm3) with orthogonal c-axes is investigated experimentally. The experiments are carried out at 77K and the samples are independently magnetized in field cooled configuration under 1.2 T. The assembly is performed by maintaining a central magnetized superconductor stationary while approaching additional trapped field magnets from left and right with their magnetization axes perpendicular to theirs neighbours. The flux density over the surface of the stationary sample is measured during the assembly of the array. A flux creep period of 45 minutes is then allowed before performing several scans of the magnetic flux density generated by the array of superconductors above the surface of the whole configuration.
The experimental distribution of the flux density above the array of trapped field superconductors is compared to a similar array made of permanent magnets. The results suggest that a reorganisation of the current density distribution occurs in the central sample when the distance between the superconductors is reduced. In spite of this phenomenon, the array of superconductors is shown to produce a field gradient as high as 10 Tm-1 at a distance of 1 cm away from the array.