Speaker
Description
This study investigates the delamination behavior of REBCO coated conductors (CCs) using the electromagnetic delamination strength (EDS) method. Unlike the mechanical delamination strength (MDS), which relates stress to structural failure, EDS focuses on the irreversible threshold at which critical current degradation occurs. This distinction is particularly important for high-field magnet applications, such as fusion magnets and particle accelerators, where REBCO CCs are increasingly utilized for their exceptional superconducting properties. However, conductors in these applications are subjected to substantial Lorentz forces, driven in part by the interaction between screening currents and the magnetic field.
The inherent weakness of REBCO coated conductors (CCs) lies in their multilayer structure, particularly the adhesion between the superconducting layer and the buffer layers. To investigate the degradation of the critical current (Ic), a custom-designed sample holder was developed, aided by numerical analyses to minimize hoop stress components and isolate the radial stresses responsible for delamination. Experiments were performed on 4 mm-wide commercial samples from various manufacturers, using magnetic fields up to 19 T and currents up to 2 kA. The relative orientation of the magnetic field and current generated an average transverse tension of up to 10 MPa. Measurements conducted at 77 K and 4.2 K were complemented by inductive mapping of the local critical current density (Jc) before and after testing, as well as SEM/EDX analyses, providing detailed insights into damage distribution and underlying mechanisms. Forensic analyses revealed compositional changes in specific regions, highlighting simultaneous quench events and localized delamination, which predominantly occurred at the tape edges. To investigate the influence of the current density profile within the superconducting layer, experiments were conducted under varying magnetic fields and temperatures. Furthermore, as 4 mm-wide tapes are fabricated by mechanical or laser slitting from 12 mm-wide tapes, the effect of the slitting process on delamination was also analyzed.
These findings offer critical insights for magnet design, identifying the conditions that cause irreversible degradation of superconducting properties and informing strategies to mitigate such effects.
