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.
We consider the scattering of time harmonic flexural waves by a through crack in a perfectly conducting plate under a uniform magnetic field. By the use of Fourier transforms we reduce the problem to solving a pair of dual integral equations. The solution of the dual integral equations is then expressed in terms of a Fredholm integral equation of the second kind. The dynamic moment intensity factor versus frequency is computed and the influence of the magnetic field on the normalized values is displayed graphically.
To protect a large-scale superconducting magnet from damages that may be caused by a quench, current capacity of the magnet conductor should be increased. However, increase in current capacity of the conductor produces serious problems of magnet technology. For examples, a large scale superconductor is hard to be wound, which is critical especially for a large scale magnet of complicated shape, and it is often liable to be suffered from instability problem due to electro-magnetic phenomena, because diffusion time of current and magnetic field across the conductor cross section is large. It is very difficult to estimate performance of a large scale conductor from that of a small scale conductor of similar figure, therefore, development of the large scale conductor needs large amount of cost and time, because the full scale conductor should be tested. To clear those problems, we propose to compose a large scale conductor by paralleling several subconductors. Each subconductor is electrically insulated from other subconductors and excited by an individual power supply. Current of each subconductor is feed-back controlled to follow a given current reference. By using this technique, flexibility of conductor can be remarkably increased without scarifying the mechanical strength against electro-magnetic force, and R & D for scaling-up of the conductor size becomes much easier. However, it is necessary to study on the controllability of subconductor currents because the subconductors are tightly magnetically coupled and an instability might be caused in the control system. Uneven current distribution in subconductors is caused by asymmetric subconductor inductance. In this paper, merits of this system are explained and the static and dynamic characteristics of the system are studied. In this study, the relation between the uneven current distribution in subconductors and constants of the excitation system is analyzed, and the stability of the control system is also analyzed. The chance of appearance of abnormal voltage during energy dump at a quench even is pointed out and a method to prevent this abnormal voltage is proposed. In the parallel conductor system, a current in a subconductor is easily transferred to other subconductors because the subconductors are magnetically close-coupled, therefore, it is possible to actively control the stability of the magnet by transferring a current in a quenching subconductor to the other subconductors. The active control of the magnet stability is also studied.