In this study, high-density magnesium diboride (MgB₂) bulk superconductors were synthesized by spark plasma sintering (SPS) under pressure to improve the field dependence of the critical current density (J_c-B) in MgB₂ bulk superconductors. We investigated the relationship between sintering conditions (temperature and time) and J_c-B using two methods, ex situ (sintering MgB₂ synthesized powder) and in situ (reaction sintering of Mg and B powder), respectively. As a result, we found that higher density with suppressed particle growth and suppression of the formation of coarse particles of MgB₄ and MgO were found to be effective in improving the J_c-B characteristics. In the ex situ method, the degradation of MgB₂ due to pyrolysis was more severe at temperatures higher than 850 °C. The sample that underwent SPS treatment for a short time at 850 °C showed higher density and less impurity phase in the bulk, which improved the J_c-B properties. In addition, the in situ method showed very minimal impurity with a corresponding improvement in density and J_c-B characteristics for the sample optimized at 750 °C. Microstructural characterization and flux pinning (f_P) analysis revealed the possibility of refined MgO inclusions and MgB₄ phase as new pinning centers, which greatly contributed to the J_c-B properties. The contributions of the sintering conditions on f_P for both synthesis methods were analyzed.

In this study, conditions for obtaining high-quality superconducting joint to a Gd-Ba-Cu-O bulk superconductor to investigate for the first time the effect of pulse field magnetization (PFM) properties of the joined bulk and to study an effective pulse magnetization method. We fabricated a good superconducting joint using the local melting method with sintered Er-Ba-Cu-O and applied the PFM method to the joined bulk. As a result, a high magnetic field of 1.2 T was trapped in the joined part when the magnetic field strength more than 5 T was applied at 50 K. From the evaluation results of the J _c - B characteristics of each region cut from the joined sample confirmed that the joined sample was efficiently magnetized due to the preferential field penetration path and the dispersion of heat generation from the joined part. This is a finding that could lead to the future use of PFM in the bulk using superconducting joint with minimal reduction of the trapped magnetic field, and could simplify the magnetization method, which has been a drawback of PFM.

The electromagnetic and thermal behavior of pulsed field magnetization (PFM) of a superconducting joined bulk was confirmed in detail by FEM simulations. It was shown that when the joined bulk is magnetized by PFM, the joined part may become the preferential field penetration path due to the difference in superconducting properties between the matrix and the joined part. However, the actual experimental system only observes the behavior of the magnetic field outside the bulk, and the details are largely based on predictions. In the actual experiments, GdBCO was selected as the matrix and ErBCO was selected as the joined part for the superconducting joint. The joined sample was cooled to 50 K and subjected to an applied magnetic field of 5 T in the PFM. FEM simulations were performed to simulate the experiments in this study. By using J _c values derived from actual measurements in the simulations, the magnetic field and thermal behavior were simulated, and it was confirmed that the joined part was the preferential field penetration path as in the experiment. In addition, the magnetic field distribution with and without joining confirms that the local melting method has no effect on the property degradation in increasing the size of the joined bulk. In addition, this system made it possible to confirm the magnetic and thermal behavior even when different REBCO materials are introduced.

The degrading of trapped fields B _T in bulk MgB ₂ superconductor due to the occurrences of flux jumps was investigated. This work presents the method for characterizing the propagation of the magnetic flux in an artificially drilled MgB ₂ bulk superconductor fabricated via spark plasma sintering (SPS). The pulsed field magnetization (PFM) was utilized by studying the effect of applied fields B _A on the bulk MgB ₂ embedded with low melting alloy of Bi-In-Sn alloy and aluminum rods within the holes which improved the thermal property, thereby suppressing the flux jumps caused by the generated heat within the bulk sample. The bulk MgB ₂ sample was redesigned to enhance both the thermal properties and to suppress flux jumps during pulse applications. We discuss the magnetic flux dissipation, the flux motion, and performance by evaluation of the capture field ratio B _T / B _P . We analyzed the field trapping performance of the improvised bulk at high applied fields and compared our findings to the data obtained for the as-received bulk sample for the penetration ratio B _P / B _A and penetrated field B _p . This study helps to solve the flux jump problem in the bulk superconductor resulting from poor heat dissipation. This is an experimental breakthrough that supports existing simulation studies and reports giving way for more prospects for high field applications in the development of bulk MgB ₂ superconductors.