Magnetic shielding of MgB2 tubes in applied DC and AC field

The magnetic shielding produced by superconducting tubes was of applicative interest in high energy physics apparatus. Except several attempts with LTS materials, up to now no HTS material has been used for this application, partly due to the low current capability and partly to the poor mechanical properties of the conventional bulk cuprates. An alternative, among the Medium Temperature Superconductor (MTS) material is represented by MgB2 in bulk form. This material can be quite easily produced at high density by the reactive liquid Mg infiltration route, generating tubular bodies of various shape and good mechanical strength. The shielding efficiency in several tubular MgB2 objects has been tested at 4.2 K, applying DC and AC fields and the criticality of the thermal instability due to flux jumps of the superconducting manufacts has been evidentiated. The possibility to shield field larger than 1 T has been demonstrated.