Magnetic separation using high-Tc superconductors

Superconductivity has found in magnetic separation one of its major industrial applications, second only to magnetic resonance imaging. Low-Tc 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-Tc 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-Tc materials are not sufficiently developed to simply replace low-Tc 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-Tc superconducting coil in a magnetic separator with an iron yoke. In this application the low-Tc 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-Tc coil as opposed to resistive ones, however, results in different design requirements, ultimately dictated by the sensitivity of the high-Tc 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.