Measurements of Magnetic Field and Temperature Dependence of the Critical Current in Bi-2212 Superconducting Wires

In this work we describe our built in-house system for the measurement of the critical current density Jc in superconductors. The set up is able to tolerate currents up to 800 A, and works in fields up to 7 T and temperatures from 4.2 K to 40 K. The peculiarity of our system lies in its versatility: we can measure a high variety of superconducting samples up to 15 cm in length, testing their performance also at temperatures achievable by cryocoolers. Magnetic field and temperature dependencies of critical current density Jc(H, T) are measured in Bi-2212 round wires. Bi- 2212 wires are fabricated by applying the new GDG (grooverolling /drawing /groove-rolling) process consisting of the alternation of groove-rolling and drawing techniques, which densifies the filaments already during the working procedure prior to the heat treatment. A Jc ? 4×105 A/cm2 in self-field at 4.2 K is measured and a Jc scaling based on the collective pinning theory is shown to hold above 2 T.