Earticle

In 2013, highly concentrated rare-earth-rich mud (REE-rich mud) was discovered around Minami-Torishima Island, presenting an opportunity to develop a new source of rare-earth elements (REEs). This study proposes a new method for selectively removing non-REE components using magnetic separation. First, we calculated the theoretical levitation positions of the target minerals using the magneto-Archimedes method, considering the mineral density, magnetic susceptibility, and magnetic field distribution of a high-temperature superconducting (HTS) bulk magnet. Next, we conducted separation experiments to selectively isolate REEadsorbed apatite from a simulated mud sample consisting of a mixture of apatite, montmorillonite, quartz, and zeolite. The results demonstrated that non-apatite minerals were successfully removed using magnetic levitation method. Based on these results, we applied the method to actual core samples (REE-rich mud) fromthe coast of Minami-Torishima Island. These experiments showed that phillipsite could be selectively separated from the core sample using magnetic levitation. However, the overall weight reduction was less significant than that achieved with the simulated REE-rich mud. This discrepancy was attributed to the inability to separate the paramagnetic mineral montmorillonite into the levitated fraction, because of its swelling property and cation exchange capacity, and location-dependent variability in the mineral composition of the core samples. Possible solutions to this problem include improving the sample dispersion and combining this method with other separation techniques.

As global environmental regulations intensify, the electrification of the mobility industry is accelerating, thereby increasing the demand for high-power electric propulsion systems. Among the various candidates for application, superconducting motors have attracted considerable attention owing to their potential for delivering exceptionally high-power density. In this study, we fabricated two types of GdBa2Cu3O7-δ (GdBCO) superconducting magnets and evaluated their trapped field performance using a 14T superconducting magnetization system. A single grain bulk magnet, grown by the top seeded melt growth (TSMG) method, exhibited a trapped field of 1.93T at 20K. The stacked tapes, fabricated by commercial GdBCO tapes, showed a maximum trapped field of 1.25T at 20K. While the single grain bulk magnet has an advantage in trapped field performance, the stacked tapes offer benefits in terms of simple manufacturing processes and shape flexibility. These results suggest that simultaneous improvement of trapped field performance and motor design optimization could establish superconducting motors as a core technology for nextgeneration electric propulsion systems.

Engineering correlations are derived to estimate the friction factor and Nusselt number of rectangular helical flow in stacks-inconduit conductors (SICC). The SICCs are under current development at KFE (Korea Institute of Fusion Energy) towards the realization of HTS (high-temperature superconductor) fusion system. A copper band is helically wound around the outer wall of a rectangular bundle of stacked REBCO (rare-earth barium copper oxide) tapes, and the space between the bundle and the external jacket serves as a cooling channel for helium gas flow. Key geometric parameters are identified for the SICC structure, and threedimensional numerical analyses are performed with ANSYS FLUENT and real thermo-physical properties of materials and fluids at 20-30 K. The analysis domain consists of (1) the REBCO bundle, (2) the copper band, and (3) the helium gas flow. A special attention is paid to the role of helix angle of copper band (and helium flow), significantly affecting not only the hydraulic diameter and flow length of cooling channel, but also the flow pattern of cooling gas established by the centrifugal force in curved flow passage. The thermo-hydraulic data are simplified with the typical method of dimensional analysis, and it is successfully verified that the dimensionless friction factor and Nusselt number can be expressed in terms of well-known Dean number (composed of inertial, centrifugal, and viscous forces), in a similar way with the helical tube flow. The derived correlations are directly applicable to the ongoing design and manufacturing of SICC, and eventually to the development of forced-flow gas-cooled HTS magnets.