Magnetic lenses using different MgB ₂ bulk superconductors

A magnetic lens allows the concentration of magnetic fields using the diamagnetism of superconductors. The important features of the magnetic lens are a tapered inner diameter from which the magnetic flux is extruded and a slit to suppress the circumference current that shields the magnetic flux. This concept was experimentally confirmed through the use of GdBaCuO bulks and a stack of NbTi/Nb/Cu sheets. We refer to this arrangement as a magnetic lens. The Mg-reactive liquid infiltration (Mg-RLI) process developed by Edison SpA is suitable for the production of large and high-density MgB ₂ bulks. Three MgB ₂ bulk magnetic lenses, each with a different microstructure, were fabricated following the Mg-RLI process. The properties of the MgB ₂ magnetic lenses were measured in a cryocooler system as well as in liquid helium. The results confirmed that the MgB ₂ bulk magnetic lenses could concentrate a magnetic field and that their field concentration properties were greatly affected by the temperature and the external field. In addition, the microstructure of the MgB ₂ bulk also had an influence on the magnetic properties at different external fields. The results indicated that the MgB ₂ lens might be utilized as a field amplifier in intermediate fields.