Magnetic separation using high-Tc superconductors

Bolt, Livia (2001) Magnetic separation using high-Tc superconductors. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Superconductivity has found in magnetic separation one of its major industrial applications, second only to magnetic resonance imaging. Low-T_c superconducting coils have been employed in High Gradient magnetic Separators (MGMS) since the late 80s, the saving in power consumption overcoming the high costs of the liquid helium refrigeration system. The discovery in 1986 of the high-T_c materials has opened the possibility of cooling with liquid nitrogen or cryocoolers, which represents a considerable simplification of the cryogenics involved and a reduction of capital and running costs. But the present high-T_c materials are not sufficiently developed to simply replace low-T_c coils in the opened solenoid configuration of the HGMS, due to their low critical currents around 77K.

This thesis investigates the employment of a high-T_c superconducting coil in a magnetic separator with an iron yoke. In this application the low-T_c coil supplies Ampere-turns to a magnetic circuit, which provides a low reluctance path for the magnetic flux and delivers a magnetic field in the air-gap much higher than the field seen by the coil.

A small prototype of such a separator has been built. The superconducting coil, a Bi₂S₂Ca₂Cu₃O₈ solenoid, has been provided by Intermagnetics General Corporation. The use of high-T_c coil as opposed to resistive ones, however, results in different design requirements, ultimately dictated by the sensitivity of the high-T_c material to magnetic fields. Finite elements modelling of the system has provided the framework for the quantitative analysis of the magnetic field distributions on the coil windings and the optimisation of the system configuration.