PERSISTENT MAGNETIZATION OF MgB[sub 2] CYLINDERS INDUCED BY A PULSED FIELD

Abstract

High stable trapped fields in bulk superconductors can be useful applied in many electrotechnical applications, as i.e. for motor/generators, for MRI systems or for magnetic separation devices. The HTS bulk materials appear as the matter of choice to this purpose and many attempts have been done on melt textured cuprates tiles, at temperatures up to 77K, applying constant magnetic fields or pulsed magnetization methods. Even if the pulse magnetization is far less effective than the DC magnetization in the trapping capability, it appears as the most friendly technique in practical devices. So we have studied the effects of the pulsed technique, applied to a bulk MgB 2 cylinder: a very promising device in view of the feasibility of similar much larger manufacts. To this purpose we have used a copper solenoid to magnetize the MgB 2 cylinder, with both cylinder and solenoid conductively cooled by a cryorefrigerator, in the range of temperatures between 5 and 20 K. This simple cryogenic arrangement can be representative of many more elaborate practical devices. Tailoring the applied pulsed field waveforms, we successfully magnetize cylinders of diameter of the order of 50 mm, reaching more that 0.5 T trapped flux density, in their centre, and the persistent magnetization is not affected by external perturbations. The parameters which regulate the trapping field performances are mainly related to the heat management of the MgB 2 cylinder.