Forces Acting on Superconductors in Magnetic Fields

Abstract

The forces acting on a superconducting body in a magnetic field may be obtained by analogy with hydro-dynamics, considering the similarity of the force field around a perfect diamagnetic with the flow field of an ideal liquid past an impermeable body of the same shape. The translation is provided by replacing ½ρv2 by (⅛π)μH2. As a practical application of the repulsive forces acting on superconductors in a diverging magnetic field, design of two types of magnetic supports for a sphere is described. In the coil-type support, two coils with opposed currents are necessary to provide stable equilibrium. Similarly, the permanent-magnet-type support requires two transversely magnetized rings with opposed polarity. The dissipation of energy in a rotating sphere by eddy currents and by viscous drag of the surrounding gas was studied. The nonexistence of any torque on a freefloating, superconducting sphere in a rotating, transverse field indicates absence of interaction between the superconducting electrons and the metallic lattice.