Experimental Measurement and Numerical Simulation of the Screening Current-Induced Field Decay in a Small ReBCO Coil

Screening currents are a major concern when designing high-temperature superconducting magnets as they can have a drastic impact on the generated field level, homogeneity, and temporal stability. Thus, the this paper will present results from an experimental and numerical study of the screening current-induced effects in a small-sized ReBCO coil. On the experimental side, two small single pancakes have been wound from 4-mm-wide Kapton-insulated ReBCO tape provided by manufacturer SuperOx and high-sensitivity Hall probes were mounted on the coils to monitor their generated field. The coils have then been tested at liquid nitrogen temperature, both at the remanent state and with transport current to measure the time decay of the screening current-induced field. The experimental systems have also been modeled for magnetodynamic simulations using the free and open-source software GetDP and Gmsh. A two-dimensional axisymmetrical FEM model of the coils has been built, accounting for the detailed layer structure of the windings. An H-φ formulation was used, using an E(J) power law for the superconductor behavior and cohomology to enforce current constraints. First results obtained with this model are presented, showing its capability to simulate screening currents in coils of several tens of turns. Yet, its accuracy and computation time will need to be further improved. The presented results are a first milestone in our investigation for efficient and inexpensive methods to simulate screening currents in ReBCO HTS coils.