Magnetic flux penetration of commercial Bi2223 wires evaluated by magneto-optical imaging

•Magnetic field penetrations into commercial Bi2223 wires have been evaluated.•Magneto-optical (MO) imaging was used to visualize magnetic field penetrations.•MO images indicate that the current flow in the wire is non-uniform.•MO images clarified the presence of defects created during the fabrication process of the wire.

We have evaluated magnetic field penetrations into commercial Bi2223 wires fabricated by high-pressure sintering process. Magneto-optical imaging with high-spatial resolution has been applied for that purpose. It is found that there are inhomogeneous couplings between filaments, which can lead to inhomogeneous and complicated current flow in the wire. We also found defects running oblique to the filaments, possibly created during the rolling process of the wire.