Study of the magnetic shielding ability in relation with the non linear E(J) relationship of melt cast Bi-2212 tubes under DC axial magnetic fields.

In this work, we aim at describing as widely as possible the shielding properties and the E(J) relationship of Bi-2212 tubes from non-destructive measurements on a whole cylinder. First, the threshold magnetic induction below which the shielding occurs, Blim, is measured in a large temperature range between 10 K and 77 K. The temperature dependence of Blim is compared to that of similar superconducting hollow cylinders made of Bi-2223 previously studied in [Fagnard J-F et al. Supercond. Sci. Technol. 22 (2009) 105002] and shows that the magnetic shielding capabilities of Bi-2212 below T = 60 K can exceed those of Bi-2223. In particular, the threshold value of shielded magnetic field is higher than 800 mT below T = 20 K with a 5 mm thick cylinder. Next, the sweep rate dependence of Blim is determined and analysed under several simple assumptions relating Blim to the shielding currents, J, and the sweep rate of the applied magnetic field to the electric field, E, to give information about the non-linear E(J) relationship. Then, the relaxation of the shielding currents is studied at several temperatures and the results are used to confirm the values of the power law exponent of the E(J) relationship determined by sweep creep experiments. Finally, transport and AC-shielding measurements are carried out and exploited, together with the magnetic relaxation and the sweep creep measurements, to build a piecewise E(J) graph that extends over several decades.