The large hardware international collaboration for fusion power has been carried out and successfully completed. The collaboration has been named as Large Coil Task (LCT) for superconducting toroidal coil under auspices of the International Energy Agency. This paper describes the overview of the task and the experimental results. A superconducting coil system is indispensable for fusion power generation in order to confine and control plasma. However, it is technically impossible to construct such large coil system with one step. The evaluation on conductor types and materials, and the scaling-up are requested to construct a practical reactor. In order to have efficient developments, an international collaboration was undertaken in 1977. The participants are the United States, EURATOM (represented by West Germany), Switzerland and Japan, of which US acted as the operating agent. The major part of the project has been devoted to six coils (5.5m height, 40ton/coil) fabrication and facility (helium refrigerator etc.) construction. As the final stage of the project, the experiment have been continuously performed from January 1986 until September 1987 in the United States. All the six coils, which brought from the participants, satisfied the original target, 8T field generation. In the extended condition, finally 9T was simultaneously obtained with all the coils.
The critical current density is an important factor as well as the critical temperature and the critical magnetic field in power application of superconductors. A magnitude of the critical current density is determined by flux pinning interactions. In this report the flux pinning phenomenon is briefly explained and it is discussed what is to be done for the purpose of increasing the critical current density. Measuring methods of the critical current density are also reviewed.