Pinning in superconductors with anisotropic defects

By calculating the volume pinning force in superconductors with anisotropic pinning centers we have shown that the critical current densitiesj _c in NbTi by both current and magnetization measurements can be explained. The critical current density in fields parallel toj _c can also be included. We conclude therefore that in superconductors with strong pinning centers the critical state is always determined by the equilibrium condition between the Lorentz force and the volume pinning force and not by the instability of the force-free configuration. By detailed investigation of thej _c dependence on field direction, useful information can be obtained with respect to the volume and surface contributions to the pinning force.