Speaker
Description
We present the integration and initial test of the world’s first superconducting magnet system for Magnetic Density Separation, from coil winding to cryostat assembly as well as first cool-down and energizing. Magnetic Density Separation is a relatively new separation technology that allows the simultaneous sorting of multiple non-magnetic materials based on their mass density by combining a ferrofluid with a strong vertical magnetic field gradient. To maximize the field gradient in the ferrofluid, the distance between the NbTi coils operating at 4.5 K and the room-temperature ferrofluid is minimized. This is made possible by two design choices: conduction-cooling allowing for a single-wall cryostat; and vertical ‘stay rods’ that support the flat top plate of the D-shaped cryostat from the stiff bottom, allowing for a relatively thin wall.
The magnet system is designed, engineered and assembled at the University of Twente and comprises 3 side-by-side 0.3 m $\times$ 1.4 m racetrack coils that are shrink-fitted in an aluminum alloy cassette, which provides thermal pre-stress to balance the Lorentz forces. The vertical magnetic field gradient at the bottom of the ferrofluid reaches 20 T/m. The coils are cooled to 4.5 K with a 1.5 W @4.2 K GM cryocooler. A particular design challenge is to minimize the cryogenic load to enable conduction cooling by meeting competing requirements imposed by the support structure, the heat load from the cold mass with a large surface area, and a significant attraction force between coils and ferrofluid.
This work is part of the research program “Innovative Magnetic Density Separation for the optimal use of resources and energy”, project number P14-07, partly financed by the Dutch Organization for Scientific Research (NWO).
