Understanding high-temperature superconductors at high fields and low temperatures for performance optimization

REBa₂Cu₃O_7-δ (RE = rare earth) compounds are the principal superconductor candidates for carrying the colossal currents needed for high magnetic field applications such as magnetic containment in compact fusion reactors, muon colliders, and high field DC magnets. While the effects of defect microstructure on REBCO behavior are well understood for high temperatures and low fields, this understanding does not extrapolate to the low temperature-high field regime. Pulsed magnets allow us to observe the novel physics emergent at the highest fields, but their use presents unique challenges, both intrinsic to the physics of large and rapidly changing fields and the technical implementations of powerful magnets, like vibration, field compensation and fast data acquisition. We overcome these challenges and present non-linear and linear electrical transport results in REBCO films with different microstructures and doping levels as a function of temperature, field strength, and orientation up to 65 T. Using non-linear transport, we measure hundreds of current-voltage curves for each (~100 ms) pulse and extract a field dependence of the critical current. Our findings show the effects of microstructure and doping on the performance of REBCO films under conditions relevant to applications.