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Open gradient magnetic separation utilizing NbTi, Nb3Sn and Bi-2223 materials

Superconducting magnets enable the magnetic separation of particles with small magnetic susceptibility. In this paper, we compare superconducting separator magnets made of Nb3Sn, NbTi and Bi-2223 materials. The separator system is used to determine the optimal conditions for separation of various slurries. The magnet should provide a high and nearly constant magnetic force density. These requirements are met with racetrack coils. Geometries consisting of one or two racetracks have been examined. In order to keep the material costs at a reasonable level, the volume of the magnet has been minimized taking into account the constraints set by the force and current densities. Sequential quadratic programming (SQP) was used in the optimization procedure. The force density has been calculated using an analytical two-dimensional model. The critical current density of the coil was obtained by solving the magnetic flux density from a three-dimensional model using the finite element method. We have compared magnetic force densities and wire lengths in magnets made of different materials. For magnets made of low-temperature superconductors, the optimized geometry consisted of two coils. For magnets made of high-temperature superconductors, the minimum volume was achieved by using only one coil.