Improving the Central Magnetic Field of an HTS Magnet Using Multiple Flux Pumps

This paper investigated the method of using multiple linear-motor flux pumps to increase the central magnetic field of an HTS magnet composed of six stacking insulated YBCO double pancake coils. In this work, we compared two different excitation methods based on linear-motor flux pumps, i.e., in series excitation and in segmented excitations, to investigate their exciting performances on this HTS magnet. Experiments showed that in the series excitation, the maximum operation current of the HTS magnet was limited by the YBCO coil of the smallest critical current. On the other hand, in the segmented excitations, both the maximum operation current of each YBCO coil and the central magnetic field of the HTS magnet were increased effectively. Moreover, in the segmented excitation, we revealed the interaction between excitation current of one YBCO coil, to the induced currents of other YBCO coils, due to their mutual inductances and different charging sequences. In addition, we found that the charging sequences had an influence on the maximum central magnetic field of the HTS magnet, due to the different vertical field on different YBCO coils, which was consistent with the simulation results. The results of this work showed that using multiple linear-motor flux pumps for excitation can effectively increase the magnetic field of an HTS magnet.