The Field Distributions in the Vicinity of a Superconducting Flux Exclusion Tube*

The distributions of the magnetic field inside and around a superconducting flux exclusion tube due to currents induced in the material by an external magnetic field are examined. A simple macroscopic model for the superconductor is assumed, based on the concept of a field-dependent critical current density, and London’s equations are used to calculate the magnetic potentials in the three regions of interest. The magnetic field inside the tube was mapped using an electron beam, and the results compared with the calculations. It is concluded that the major contribution to the magnetic field present in the tube can be ascribed to the induced dipole and sextupole current distributions in the superconductor. By contrast, the effect of direct field penetration through the narrow slits in the structure is very small. (Submitted to J. Appl. Phys. ) *Work supported by the U. S. Atomic Energy Commission.