A novel magnet/superconductor heterostructure for high-field applications

The effect of magnetic shielding on the current and field distributions in a thin, flat superconductor ring located between two coaxial cylindrical so ft magnets of high permeability is studied. Such a heterostructure protects the flux-free state of the ring even in the presence of strong total super currents, with concomitant high magnetic fields and low electromagnetic los ses in ac applications. An integral equation governing the current distribu tion in the Meissner state of the ring is derived and solved numerically fo r different relative permeabilities of the magnets and various distances be tween the magnets and the ring. This reveals that the current distribution tends to become homogeneous when the relative permeabilities are increased, the effect already saturating at values of these quantities of the order o f a few hundred. When the distances between the magnets and the ring are re duced, the current peaks near the circumferences of the ring decrease, ther eby contributing to the large total supercurrent.