Study on Method to Suppress Decay of Trapped Magnetic Fluxes in the HTS Bulk Subjected to Perturbation of External Magnetic Field by Use of Shielding Coil Wound of HTS Wire

Trapped magnetic fluxes in HTS bulks are decayed when the bulks are subjected to perturbation of external magnetic fields. In HTS bulk apparatuses such as HTS bulk motors and magnetic levitation bearings, there is a possibility that the trapped magnetic fluxes in the bulks disappear because the bulks are inevitably subjected to perturbations of the external magnetic fields. For those apparatuses to work stably and reliably, it is necessary to develop methods to suppress the decay. It was shown in our previous experiments that the decay is caused by temperature rises of the bulks due to AC losses in the bulks. The authors proposed a method to put a shorted shielding coil wound of HTS wire around the bulk aiming at reduction of the AC losses in the bulk. It was experimentally shown by use of a shielding coil wound of Bi/Ag sheathed wire that the decay of the trapped magnetic flux was effectively suppressed. In this paper, shielding performance of the coil wound of GdBCO wire was experimentally investigated comparing with that of the coil wound of Bi/Ag sheathed wire. AC losses in the bulks and shielding coils are calculated for various arrangements of the shielding coil to find a preferable shielding coil arrangement from stand points of shielding performance and reduction of AC losses.