Upper limit of the critical currents and magnetic fields of cylindrical coils made of Bi(2223)Ag tapes with reduced -anisotropy

The results of model calculations of the critical currents of silver sheathed Bi(2223) multifilamentary tapes with reduced -anisotropy, which can be achieved by assembling the filaments into several preferred orientations with respect to the external transverse magnetic field, are presented. Such tapes can be prepared by a two-axial rolling technique. It is shown that the properties of tape with higher disordered orientation of the filaments will approach those of isotropic tape. The characteristics of this new class of tapes have been constructed with respect to the angular dependence of the mutual orientation of the magnetic field and the tape surface. A comparison of the evaluated critical current values with those of an original tape with the same cross-section was performed. Further, these data were used for calculation of the critical current of a small model magnet consisting of cylindrical pancake coils. Unexpected results were obtained, showing that practically no appreciable change in the absolute value of the resulting critical current of the magnet can be achieved when the magnet winding is made of the tape with reduced anisotropy. It is shown that the increase in the critical currents of some turns is accompanied by the simultaneous decrease of the critical currents of other turns. However, a slight increase in the magnet critical current at 77 K could be achieved by combining both tape types in the winding, i.e. the tape showing considerable anisotropy and the tape with reduced anisotropy. The influence of the tape widening on the resulting engineering current density is discussed.