Magnetic shielding capability of MgB2 cylinders

The shielding of a DC magnetic field has been demonstrated to be complete at 4.2 K, at least up to 2 T, inside the 18 mm bore of a thick MgB2 bulk cylinder, 70 mm tall. No hysteresis has been detected along the cycle of the field application and removal, and no flux jumps have been detected either. The MgB2 cylinder was manufactured by the Reactive Mg Liquid Infiltration process, an 'in situ' technology able to give very dense MgB2 manufacts. According to the previously measured J(c)(B, T) characteristics of a MgB2 bulk superconductor of the same origin and quality, a critical current density of about 30 kA cm(-2) can be assumed at the fields of 2-3 T and at the temperature of 4.2 K of the reported shielding experiment. Accordingly, we estimate that the thickness of the MgB2 cylinder filled by the shielding currents is about 5.75 mm, lower than the present cylinder thickness of 8.77 mm.