Fundamental Electromagnetic Configuration for Generating One-Directional Magnetic Field Gradients

Abstract

In this paper electromagnet layouts are presented that generate a magnetic field with a magnitude gradient that does not vary significantly in a horizontal plane but decreases monotonically with the vertical height above the magnet. Such a one-direction magnetic field gradient is a specific requirement for magnetic density separation, a novel recycling technology that combines a vertical magnetic field gradient with a ferrofluid to separate a mixture of non-magnetic materials based on their mass density. The authors are assembling the first superconducting magnet to be used for this application. In contrast to other separation technologies that use a ferrofluid, multiple products can be separated in a single process step.First, the idealized current distribution is introduced that produces such a magnetic field with a magnitude that decays only in one direction. This ideal field can be approximated with practical coil configurations, which are evaluated with Fourier analysis to derive an optimal cross-sectional layout based on flat racetrack coils. The analysis concludes with a discussion of the effect of winding pack thickness on the value of the magnetic field above the magnet system and on the peak field inside the winding pack. The conclusions of this study are applicable not just for magnetic density separation, but for any application that requires a magnetic field gradient that changes only in one direction.

Thermal and electrical design of superconducting demonstrator for magnetic density separation

“…Here coil 2 is the middle coil, as indicated in figure 13. The geometry of the coils is derived in [8,14].…”

“…As with many sustainabilityrelated technologies, superconductors can enhance the performance significantly [13]. For a discussion on the benefits superconducting magnets can bring to MDS compared to the state-of-the-art permanent magnets employed in this technology, the reader is referred to [14].…”

“…The peak magnetic field at the full operating current of 300 A is 5.2 T and the average magnetic field magnitude at the bottom of the fluid bed is 2.0 T. The present manuscript focuses on the thermal design of the magnetic system, and on the electrical circuits used to excite and protect it. The electromagnetic design of the magnet is detailed in [8,14,15], and the mechanical design in [16].…”

Mechanical design of a superconducting demonstrator for magnetic density separation

“…MDS is a new recycling technology that allows to separate non-magnetic materials based on their mass density [1][2][3][4][5][6] and that ideally requires a magnetic field with a magnitude that only changes in the vertical direction. Such a one-directional magnetic field gradient requires a dedicated electromagnet design, as discussed in [12,14].…”

“…The demonstrator magnet will be the first superconducting MDS system. The advantages of superconducting electromagnets compared to the permanent magnets currently used in this technology are discussed elsewhere [12]. A comparison of the performance obtainable for MDS with various technical superconductors is made in [13].…”