| This dissertation describes how forces in magnetic levitation systems can be increased by using YBa2Cu3Oy high temperature superconductors (HTS) cooled in the uniform field of an electromagnet (2.3 T), instead of ferromagnets. The HTS, cooled in a field greater than its maximum trapped field (Bt,max), is in the fully saturated critical state (fcsat). Hence, it produces fields equal to its Bt,max, up to 1.6 T in this work. Since commonly used permanent ferromagnets (PM), of the size used in this work, produce only up to 0.5 T, replacing the PM in levitation systems with such HTS "trapped field magnets" significantly increases the magnetic fields and thus the levitation forces.; We also cool HTS in zero field (zfc) or adjacent to a PM or fc sat HTS (fcadj). We thus study six configurations of PM - HTS or HTS - HTS levitation: a PM or a fc sat HTS opposed by either a zfc, fcsat, or fcadj HTS. Levitation forces and lateral forces, as well as their behavior in multiple cycles of approach and retreat, are investigated.; Compared to levitation systems with PM, forces increase by a factor of four to ten in configurations with fcsat HTS. Up to 393 N (125 N/cm2) are obtained. In multiple cycles, forces decrease 10--40% during the first 5--10 cycles, but then stabilize at a constant level.; Experimental force-distance curves were fitted to phenomenological models. Furthermore, force maxima were calculated as functions of the maximum trapped field of the HTS following Bean's model. Lateral forces were used to estimate the stability of the different configurations. Arrangements of several zfc samples with high levitation force and good stability were demonstrated. |
