Influence of an axial current density stepping on the critical currents and magnetic field of cylindrical magnets wound with Bi(2223)Ag anisotropic tapes - theoretical analysis

Theoretical analysis of the influence of the stepped current density in the winding on the critical currents of the magnets consisting of axisymmetric cylindrical pancake coils which are wound with the anisotropic Bi(2223)Ag tapes was performed. On the basis of extensive numerical calculations we have shown that the slight increase in the critical current of the magnet can be expected if the stepping of the current density in the winding is done in such a way that either the overall turn number in the areas close to the magnet flanges is decreased without changing the geometry (Method A), or the pancake coils situated in these areas are wound with two parallel tapes (Method B). As for Method A, there is practically no difference in the change of the positions of the weakest spots in the winding if compared with the case of the magnet with the same geometrical dimensions and the uniform current density. The weakest turns are located in the pancakes which are close to the magnet flanges. As for Method B it has been shown that the relatively higher increase in the magnet critical current is accompanied by the movement of the positions of the weakest spots to the inner parts of the winding. Since the number of the overall number of turns decreases considerably and the increase in the magnet critical current is slight, the magnetic field in the magnet center is always decreased. This means that any of the two methods analysed above is not suitable as the method leading to the design and construction of the magnets with increased magnetic field. (C) 1998 Elsevier Science B.V. All rights reserved.