Speaker
Description
Rare-earth barium copper oxide (REBCO) coated conductors (CCs), the leading candidates for the construction of ultra-high field magnets, are produced in the form of thin tapes, with a laminar structure consisting of different layers of functional materials. The feeble adhesion strength between layers has been long remarked, and represents a major concern for magnet design, as it imposes hard bounds on the allowable tensile stress through the materials’ interfaces. Post-mortem analyses on conductors deconstructed from high-field test coils have shown signs of delaminated and fractured regions, often coinciding with burnt locations considered as the limiting damage of the coils, leading to the concept of quench concomitant to delamination (QCD).
To date, research in the literature has focused on the mechanical delamination strength (MDS) of REBCO CCs, i.e. the delamination strength measured under mechanical loads. However, the non-standardized nature of the testing methods, as well as their mere mechanical aspects, has raised uncertainty on the scalability of the measured strength on an isolated sample to what a conductor would exhibit when inserted in an operating magnet configuration.
For this reason, in the applied superconductivity laboratory of the University of Geneva, an experiment has been set up to study the electromechanical delamination strength (EDS), i.e. the delamination strength when the tape is subjected to Lorentz forces, a scenario in which the conditions of the conductor approach those of when operating in a magnet configuration.
In this contribution, we report on the numerical analyses that accompany the experimental campaign, both in the evolution of the hardware and in the interpretation of the results. After introducing the experiment, we analyze the stress state inside the REBCO layer when subjected to Lorentz forces, assessing the impact of modeling approximations and experimental uncertainties. We then highlight the limiting factors and considerations that led to a new sample holder, and we evaluate the improvements in terms of stress state in the superconductor. Finally, we present the interpretation of the experimental results through the numerical models, linking the observables of the experiment, i.e. critical current and degradation current, to the measured EDS of the REBCO CCs.
