A Solid Nitrogen Cooled Linear Levitating System Based on $\hbox{MgB}_{2}$ Bulks

An innovative linear levitating system based on MgB
₂
bulks produced by the reactive liquid infiltration method is designed and built. Details of the system are presented. The levitation performance is also evaluated by means of previous experimental data. The linear levitating system consists of four MgB
₂
arc-shaped tiles lodged inside a double-shell Dewar sliding on a guide made of Nd-Fe-B permanent magnets. The magnets on the guide are properly arranged in a flux shaper configuration in order to produce maximum stiffness. Each MgB
₂
bulk has a curvature radius of 165 mm (arc length of 200 mm), thickness of 10 mm, and width of 70 mm. The system is cooled by means of a solid nitrogen heat sink. Helium gas supply to a heat exchanger is used in order to cool down the MgB
₂
slabs and the nitrogen at a temperature in the range of 20-30 K. When the flow of helium gas is interrupted, the temperature of the solid nitrogen remains below 39 K for half an hour. During this time interval, levitation measurements can be performed. Experimental verification of the cooling concept has been carried out successfully.