Effect of Screening Currents on the Field Quality of HTS Pancake Coil Magnets

High-temperature superconductors (HTS) have attracted increasing attention for their ability to carry very high current densities at relatively high temperatures, enabling the development of compact magnets capable of generating strong magnetic fields. These materials are of particular interest for applications in fusion reactors. This thesis focuses on the electromagnetic behavior of HTS pancake coils, investigated through numerical simulations to analyze how the geometric configuration and the current distribution affect coil performance. The study specifically examines the phenomenon of screening currents, their influence on the central magnetic field, and the dependence of the maximum injectable current on coil geometry. The modeled geometry is comparable in scale to the superconducting components of gyrotrons, although the results obtained have more general relevance. Three configurations were analyzed: a single pancake, a stack of four pancakes, and a complete ten-pancake coil. The simulations considered different current ramp profiles to evaluate screening current induced fields (SCIF), field relaxation (drift), and the resulting magnetic field quality. The results show that increasing the number of pancakes amplifies the deviation from the ideal current distribution and reduces the maximum injectable current. Screening current effects become more pronounced as the stack grows, leading to partial current penetration and magnetic field non-uniformities, particularly in the central region of the coil. The most effective mitigation strategies are the inclusion of a central double pancake or the injection of higher current in the central pancakes, improving field uniformity and overall performance.