Homogeneous current distribution in a coaxial superconductor with and without return current path

We have developed a theoretical method based on magnetic flux conservation between adjacent layers. One of the advantages of this method is that we can directly obtain twisting pitch and radius for realizing homogeneous current distribution in coaxial multi-layer superconductor. A set of the obtained twisting pitch and radius was employed in a sample three-layer conductor comprised of silver-sheathed multi-filamentary BSCCO-2223 tapes and the current distribution was measured by Rogowski coil. Agreement between the experiment and the theory on current distribution is quite remarkable. Using this theory, we analytically investigated influence of the manufacturing error of twisting pitch and radius on current distribution. The results revealed that the manufacturing errors of twisting pitch and radius have large effect on current distribution and a suitable set of twisting pitch and radius against manufacturing error can be found. We also investigated the relationship between twisting pitch and current distribution in coaxial six-layer conductor with return current path. The characteristics of twisting pitch in the conductor with return current path are different from those of the conductor without return current path.