30 years of conductors for fusion: A summary and perspectives

Three decades of conductor R&D, prototypes, model coils and actual fusion devices are reviewed with special attention to the drivers of the design. The conductor options are affected by the requirements typical of the fusion devices (large size and stored energy, high field, heat removal rate). The mechanical loads, operating voltage, ac loss and stability further restrict the freedom of the designer. On the other hand, the evolution of the available technologies for cryogenics and superconducting materials opens new frontiers for performance, reliability and cost. The lessons learned from the a dozen superconducting fusion devices are highlighted, starting from T-7, through MFTF, T-15, TRIAM, Tore Supra, LHD till the newest projects in construction, W-7X, EAST, SST-1, KSTAR. Some discussion is also devoted to the lessons that we keep refusing to learn.