Speaker
Description
The Future Circular Collider (FCC-hh) project, proposed by CERN with a target collision energy of 100 TeV, stands at the forefront of particle physics research. Advancements in superconducting wire technology are crucial for developing the required 16 T superconducting dipole magnets necessary to guide the proton beams. Nb$_3$Sn emerges as the most promising superconducting material for making these high-field dipole magnets. However, the critical current density (J$_C$) of state-of-the-art wires is currently 20% below the targeted performance of 2500 A/mm² at 16T and 4.2K. The critical current density of Nb$_3$Sn is inversely proportional to the material grain size. Therefore, one potential route to meet the FCC specification is to develop methods that limit the Nb$_3$Sn grain coarsening during phase formation. To achieve this, at the University of Geneva, we are employing the internal oxidation process, utilizing Nb-Ta alloys with oxygen-affinity elements such as Zr or Hf, along with an oxygen source (SnO$_2$). During synthesis, the oxygen source reacts, forming nano-ZrO$_2$ (or HfO$_2$) precipitates that inhibit grain growth. The achieved refinement of the grain size from 110 nm to 50 nm enhances the J$_C$ to 3000 A/mm² at 16 T and 4.2 K in an Hf-based wire and to 2700 A/mm² in a Zr-based wire. These wires, incorporating Hf, Zr, and the oxygen source, exhibit an upper critical magnetic field (B$_{C2}$) exceeding 29T, surpassing the values achieved in commercial wires by more than 1T. Currently, we are implementing this technique in multifilamentary wires, with the goal of developing scalable methods for industrial production. Introducing the oxygen source remains a challenge, as industrial standard wires consist of ductile metals without powders. Various implementation routes will be presented and discussed.
