パラレル導体を用いた超電導マグネットの特性

Abstract

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.