YBCO Coated Conductors for Fusion Magnets

Coated conductors (CCs) are considered as an alternative to low temperature superconductors in fusion magnets. High magnetic fields are needed to confine the plasma, which can be generated by YBCO coated conductors at relatively high temperatures (50-77 K). The critical current densities of CCs improved continuously during the last few years and the production was scaled up. The conductors will be exposed to neutron radiation in a fusion magnet, which could potentially improve or degrade their properties. Industrial YBCO coated conductors were characterized by magnetization and direct transport measurements in magnetic fields of up to 15 Tesla and at temperatures between 50 and 85 K. The critical current, its anisotropy and the irreversibility line were determined. The measurements were performed on different samples, which were sequentially irradiated up to a fluence of 2 times 10²² m^-2 (two times the ITER specification). The measurements were repeated after each irradiation step to investigate the change in the superconducting parameters. Depending on the production process of the CC and on the actual operation conditions, an increase or a decrease of the critical current density is observed. The measurements show that the performance of the CC nearly reaches the required specification for ITER conductors at present. Neutron irradiation generally does not degrade their properties in the operating range of fusion magnets.