Shielding current analysis in HTS film containing cracks: application to contactless measurement method of critical current density

Anumerical method is developed for calculating the shielding current density in a high-temperature superconducting (HTS) film with a crack. When an HTS film contains a crack, an integral-form boundary condition is also imposed on the crack surface. Since the condition is directly incorporated into the weak form, the numerical solution does not alwayssatisfyFaraday'slawonthecracksurface.Inordertoresolvethisproblem,thefollowingmethodis proposed:a virtualvoltageshouldbeappliedalongthecracksurfacesoastomakeFaraday'slaw numerically satisfied.By means of the proposed method, the permanent magnet method is investigated numerically. The results of computations show that, if the distance between a magnet and a crack is less than a certain limit, the accuracyis degraded remarkably.