CURRENT DISTRIBUTION IN SUPERCONDUCTING CABLES DUE TO FIELD CHANGES AT THE END PORTIONS OF MAGNETIC SYSTEMS

The spatial inhomogeneities of applied magnetic field change the curre nt distribution in strands of superconducting cables notably. We focus here our attention especially on the effects caused by the inhomogene ous magnetic fields at the ends of the magnet winding where the field changes considerably along the conductor in most magnet systems. The g eneral diffusion equation for the magnetic field penetration into cabl es is used to find the solutions for the induced currents in the stran ds. Some general results are given for the additional AC losses and th e induced currents in the strands in the low frequency limit. These re sults are compared with the properties of cables in homogeneous applie d magnetic field. It is found that the additional losses in the field region are negligible and the losses in the 'field-free' region are ne arly the same as if the applied field acted on the whole cable length I. The current distribution in the strands is strongly influenced by t he length a, in which the applied field is changing at the cable ends. The minimal enhancement of the largest induced currents J(2m) in the strands is for very short values of a, being twice as high for a = 0 t han for the infinite cables in homogeneous applied fields. This enhanc ement of the induced current, decreasing the critical current of the c able, can be important for the stability of some magnets. Only for the central part of the cable can one minimize the value of J(2m), in the strands by choosing appropriate values of the lengths I and a.