Quasi-Round HTS Conductor Using REBCO Tapes for Fusion Magnet Application

A great progress in the electrical performance of high-temperature superconductor (HTS) REBCO tapes allows for a much increased transport current capability in cables especially at high magnet fields. This is of interest to future fusion magnet applications. A variant type of twisted stacked-tape cable called quasi-round twisted stacked-tapes conductor (QisTac) is proposed and developed for the superconducting conductor of the China fusion engineering test reactor. The stack of the twisted HTS tapes is wrapped by a tight spiral made with copper wires. The stack with the copper wire is, then, soldered to form the solid round conductor, which is reliable and easy to manufacture in long lengths. A QisTac sample with four REBCO tapes was prepared and measured at 77 K and in the self-field condition. The measurement result shows the expected critical current calculated from the individual tapes considering the self-field effect. The bending characteristic of the sample was also tested under different bending radii. The critical current is reduced by roughly 5% at 0.54% bending strain. Some residual bending strain is maintained when the maximal bending force is released. This result is promising, but reproducibility testing and tests at high field and current are needed for future high field application.