The electric field jump-detection of damaged Nb barrier in MgB2 wires annealed under pressure

In this paper we present the results of critical current (I-c) measurements of MgB2 wires made with two different set-ups of the four-point probe method: current sweep type-constant magnetic field and increasing current, and field sweep type-constant current and rapidly increasing magnetic field. Results from magnet field sweep type measurements can be interpreted by a new physical concept-a jump of the electric field in low magnetic fields. This physical concept can be correlated with damages in the Nb-barrier existing in the MgB2 wire and be employed as a detection scheme. The damage in Nb barrier reduces critical current density (J(c)) and complicates the study on critical temperature (T-c), upper critical field (B-c2), irreversible magnetic field (B-irr), pinning force (F-p), and pinning centers in superconducting MgB2 wires. Our proposed method to detect damages in Nb barrier would benefit efforts in development and applications of MgB2 wires.