Self-field redistributions and strain effects observed by magneto-optical imaging in Bi2212 multifilaments

Magneto-optical (MO) imaging was used to study and characterize superconducting Bi2212 multifilaments melted in a 5 T magnetic field. MO investigations were performed in presence of a transport current, with and without the superposition of an external magnetic field (30 mT). Transport current redistributions via the Ag cladding have been observed in MO self-field experiments for the first time in Bi2212 multifilaments. MO in situ investigations under tensile stress reveal a slow progression of the cracks, that do not cross the entire section of the multifilamentary tape. This crack formation is correlated with the transport critical current versus strain curves: the critical current drop under tensile stress is relatively smooth for Bi2212 multifilaments.