Alternative assembly process of superconducting linear Halbach array

Large magnetic forces can be achieved with a compact system by combining several permanent magnets with non-parallel magnetization directions in a so-called “Halbach array”. The saturation magnetization of the magnets involved is however a fundamental limitation impeding the performance of this configuration. The use of trapped field superconducting magnets instead of permanent magnets could therefore allow the generation of larger field gradients. Nevertheless, it was shown that when using bulk, large grain melt-textured YBCO superconductors in the array, a modification of the current density distribution occurs during the assembly process, which limits the field generated by the system.

A two-steps procedure aiming at remagnetizing the superconductors of the array after the assembly is proposed and investigated experimentally in this work. The first step consists in maintaining two closely spaced magnetized superconductors stationary while approaching additional trapped field magnets from left and right with their magnetization axes perpendicular to their neighbours. During the second step, one of the central samples is removed from the array. The experiments are carried out at 77 K both with bulk YBCO superconductors (~14×14×14 mm3) and with stacks of 2G YBCO tapes from Superpower (~12×12×12 mm3). The samples are magnetized in field cooled configuration under 1.2 T.

The flux density measured over the array is compared to analytical results and finite-element simulations. The results show that a remagnetization of the central sample occurs during the second step of the procedure. The proposed assembly method allows to increase by 15% the flux density generated 1 mm away from the array.