Critical current anisotropy in Ag/(Pb,Bi)2Sr2Ca2Cu3O10+xmultifilamentary tapes: influence of self-magnetic field

Abstract

Two factors affect critical current anisotropy in multifilamentaryAg/(Pb,Bi)2Sr2Ca2Cu3O10+xtapes - the intrinsic material anisotropy and the geometry. Experimentalresults on the magnetic field dependence and anisotropy of the criticalcurrent in a multifilamentary Ag/(Pb,Bi)2Sr2Ca2Cu3O10+x tape after correction for self-magnetic fieldeffects were found to fit the anisotropic Kim relation. Based on this relationa finite-element-method numerical code for solving the nonlinear Poissonequation for vector magnetic potential was adopted. It allowed theexperimental data to be reproduced by back calculation and made possible thestudy of the interplay of self and external magnetic fields in different caseswith well defined physical parameters of the material. The model was used toanalyse the distribution of the critical current in individual filaments aswell as to evaluate the influence of their geometrical arrangements on thecritical current of the tape. The self-field critical current of an individualfilament `extracted' from the tape was compared with the critical current ofthe overall tape. The effect of the self-magnetic field on critical currentdistribution obtained by the cutting method was determined. The criticalcurrents of the tapes with different cross sections were calculated andcompared with experiments and the influence of the self-field was analysed.The anisotropic properties of a low anisotropy architecture of amultifilamentary Ag/(Pb,Bi)2Sr2Ca2Cu3O10+x conductor were studied. The dependence of critical currents(normalized to self-field critical currents) on external magnetic fieldcorrected for the self-field was found to follow nearly the same curves asthose for tapes with different critical current densities (in the range20-70 kA cm-2 in a self-field), which makes the numericalmodel applicable to different tapes.