Anisotropy of the critical current in solid solution superconductor NbTi

Abstract

The critical current densities depend on density, size and distribution of pinning sites. Changing the round diameter of a superconductor causes an isotropic change of their distribution. By this an isotropic change of current densities is caused. Anisotropic change of the pinning site distribution by flattening causes an anisotropy of the current density. In the case of the induction perpendicular to the flat area a decrease of the critical current density is expected. In the case of the induction parallel to flat area an increase of j <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> is expected. Monocore NbTi conductors with different densities of α-Ti precipitates have been flattened with different aspect ratios and critical current densities for both cases <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B \parallel F</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B \perp F</tex> have been measured with the following results: The anisotropy factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j_{c\parallel} / j_{c\perp}</tex> depends on the critical current density of the original round shaped conductor and on the aspect ratio for high critical current densities it is independent of B. Decreasing density of pinning sites, which means decreasing current density causes dependence of the anisotropy factor on the induction B.