Performance of the First 80-kA HTS CICC for High-Field Application in Future Fusion Reactors

A promising way to realize controlled nuclear fusion involves the use of magnetic fields to control and confine the hot plasma configuration. This approach requires superconductor magnets operating above 15 T for the next generation of fusion devices. Due to their high in-field transport current capacity, rare-Earth barium copper oxide (REBCO) coated conductors are promising materials for manufacturing of cable-in-conduit conductors (CICCs) for fusion. However, the high-aspect-ratio geometry makes it difficult to find a multi-tape CICC configuration that fulfills the high engineering current density requirements while retaining enough flexibility for winding large-scale magnets. Moreover, the multilayer structure and inherent brittleness make the REBCO tapes susceptible to degradation during CICC manufacturing and operation. For more than a decade, the development of a reliable REBCO-based CICC that can sustain the huge combined mechanical, thermal, and Lorentz loads without degradation has been ongoing, albeit with limited progress. In this paper, we report on a prototype REBCO CICC that can withstand an applied cyclic Lorentz load of at least 830 kN·m⁻¹, corresponding to a transport current of 80 kA at 10.85 T and 4.5 K. To our knowledge, this is the highest load achieved to date. The CICC uses 288 tapes wound into six strengthened sub-cables, making it capable of having a current sharing temperature, T_cs, of around 39 and 20 K when operated under 10.85 T with a current of 40 and 80 kA, respectively. Scaled to a 20-T peak field and 46.5-kA transport current, this provides a temperature margin of over 10 K with respect to an operating temperature of 4.5 K. In addition, no perceptible transport current performance degradation was observed after cyclic Lorentz loading, cyclic warm-up/cool-down (WUCD), and quench campaigns. The proposed REBCO CICC is a milestone in the development of high-temperature superconductors for large-scale and high-field magnet applications.