Theoretical analysis of HTS windings made of Bi(2223)/Ag tapes prepared by a tape-in-rectangular tube technique

Anisotropy in I/sub c/(B) characteristic of Bi(2223)/Ag tapes results in a considerable decrease in magnet critical current, if the magnet winding is only made with the multifilamentary tape prepared by a standard powder-in-tube (PIT) technique. In case of cylindrical windings, the turns in pancake coils, which are located at the magnet ends, have lower critical currents than those in the other parts of the winding. In order to eliminate this undesired effect, an intensive effort is exerted to develop the tapes which have the filaments with the c-axis oriented in some other direction than the perpendicular one to the broad tape face of the tape is. In this work we present the results of calculations of critical currents of individual turns if such tapes, prepared by a novel tape-in-rectangular tube (TIRT) technique, are utilized in different parts of the winding. The analysis shows that the magnet design has always to be carried out with respect to both the magnetic field distribution in the winding and the specific properties of the tape to be used. This means that the orientation of the filaments in the TIRT tape of each pancake is to be determined with respect to the properties of the local magnetic field. This technology, which may lead to higher critical currents of individual turns, and consequently to higher critical current of the magnet, is discussed together with the natural limitations of engineering current density with respect to practical aspects of applying tape-in-rectangular tube technique to production of the Bi-based tapes with specifically oriented filaments.