After summarizing the development of the superconducting magnetic separation (SC-MS) in the world mainly for kaolin clay and coal, construction and experimental results of the miniature experimental equipment in Chinese Academy of Sciences (CAS) are presented in details. The present status of the industrial prototype SC-MS separator now under construction in CAS is also described.
In the structure of any cryogenic system, thermal isolation of the low temperature environment must be achieved effectively. Fundamental thermal insulation techniques and heat transfer mechanisms are shown in the framework of cryostat design described below. Heat leaks onto a low temperature environment through the thermal insulation of the cryostat can be devided into three different mechanisms. (1) Gas conduction in void spaces contained between the insulation materials. (2) Radiation across these void spaces and through the components of the insulation. (3) Solids conduction through the insulation materials and contact heat transfer between individual components of the insulation. The type of vacuum insulation, such as evacuated powder insulation, plain vacuum insulation, and multilayer insulation (MLI), must be chosen suitably for a given cryogenic application. The selection must be aided by a study of the heat transfer in the particular vacuum insulation.
In complicated magnet systems such as ones for fusion plasma experiments, or in multiplyt-wisted AC superconducting cables, multifilamentary composite superconductors are exposed to the external magnetic field with longitudinal component that is parallel to the conductor axis as well as transverse component. The transverse magnetic field makes the current distribution in the conductor uniform. The longitudinal magnetic field also influences the current distribution in the conductor. The cross section of conductors generally consists of the saturated region where filaments carry their critical current and the non-saturated region. The magnetic flux enclosed by one pitch of the electrical center lines of two adjacent filaments with the same azimuthal angle should be zero in the non-saturated region. With this condition, the current distribution in multifilamentary superconductors that carry the trasnport current and are exposed to the external magnetic field with both the longitudinal and transverse components is calculated. The thickness of the saturated region at the stability limit against thermo-magnetic instabilities is calculated to evaluate the transport current at the stability limit. The longitudinal magnetic field is possible to make the saturated region thicker, and to degrade the transport current at the stability limit. Increasing filament diameter and/or magnitude of transverse magnetic field increase the transport current at the stability limit, because they make the current distribution uniform and decrease the thickness of the saturated region. Increasing critical current density and conductor radius decrease the ratio of the transport current at the stability limit to the critical current. Quench current degradation due to thermo-magnetic instabilities induced by the longitudinal magnetic field should be taken into considerations when we design superconductors for complicated magnet systems.