Superconducting cables in spatially changing magnetic fields near the end portions of magnetic systems

摘要

From basic considerations for the electromagnetic coupling of different current loops in superconducting cables, the general diffusion equation for the magnetic field penetration is derived. It is shown that the model is identical to the network model used in computer calculations for the current distribution in the strands of the cable. The obtained equations enables us to consider also the effects connected with the spatial inhomogeneities in the applied magnetic field, in the contact resistance between different strands, as well as in geometrical properties along and across the cable. We focus then our attention to the effects caused by the inhomogeneous magnetic fields, especially at the ends of the magnet winding where the field changes considerably in most magnet systems. Some general results are given for the additional AC losses, the induced currents in the strands and their time constants. These results are compared with the properties of cables in homogeneous applied magnetic field.