Impact of deoxygenation/reoxygenation processes on the superconducting properties of commercial coated conductors.

We report the evolution of the superconducting properties of a commercial coated conductor during deoxygenation and reoxygenation processes. By analyzing the changes on the critical temperature, Tc, and critical current density, Jc, at 4 and 77 K, we have identified the conditions that cause a complete deoxygenation of the coated conductor and, also, the reoxygenation conditions that allow a recovery of the superconducting properties. A complete suppression of superconductivity happens at ~ 500-550 °C under a pure argon flow. After a complete deoxygenation, we observed that a reoxygenation process at ~ 400-450 °C in pure oxygen flow allows, not only a full recovery, but even an improvement in Jc, both at 4 and 77 K. Such an increase of Jc is kept or even enhanced, especially at 77 K, in the presence of magnetic fields up to ~ 6 T. A microstructural analysis by transmission electron microscopy did not give evidence of major differences in the densities of Y2O3 nanoparticles and stacking faults between the pristine and reoxygenated samples, suggesting that these defects should not be the cause of the observed enhancement of Jc. Therefore, the combined action of other types of defects, which could appear as a consequence of our reoxygenation process, and of a new level of oxygen doping should be responsible of the Jc enhancement. The higher Jc that can be achieved by using our simple reoxygenation process opens new parameter space for CCs optimization, which means choosing a proper pO2-temperature-time trajectory for optimizing Jc.

Progresses and challenges in the development of high-field solenoidal magnets based on RE123 coated conductors.

Recent progresses in the second generation REBa2Cu3O7 - x (RE123) coated conductor (CC) have paved a way for the development of superconducting solenoids capable of generating fields well above 23.5 T, i.e. the lim it of NbTi-N b3Sn-based magnets. However, the RE123 magnet still poses several fundamental and engineering challenges. In this work we review the state-of- the-art of conductor and magnet technologies. The goal is to illustrate a close synergetic relationship between evolution of high-field magnets and advancement in superconductor technology. The paper is organized in three parts: (1) the basics of RE123 CC fabrication technique, including latest developments to improve conductor performance and production throughput; (2) critical issues and innovative design concepts for the RE123-based magnet; and (3) an overview of noteworthy ongoing magnet projects.