Understanding stable levitation of superconductors from intermediate electromagnetics

Levitation experiments with superconductors in the Meissner state are hindered by low stability except for specifically designed configurations. In contrast, magnetic force experiments with strongly pinned superconductors and permanent magnets display high stability, allowing the demonstration of striking effects, such as lateral or inverted levitation. These facts are explained by using a variational theory. Illustrations based on calculated magnetic field lines for various configurations are presented. They provide a qualitative physical understanding of the stability features. (C) 2006 American Association of Physics Teachers.