Element addition plays an important role in the improvement of the physical properties of the Nb₃Sn phase itself and of growth kinetics in the Nb₃Sn diffusion reaction process. This paper first reviews the fundamental reaction behavior between Nb and Sn in the presence of Cu, which is the integral element for the thick Nb₃Sn layer formation at a low temperature reaction, and interprets it in view of Sn chemical potential. Then the paper reviews several advanced element additions to realize breakthrough grain refinement, touching on their grain refinement mechanism. Subsequently, the recent topic of Ti and Ta addition is examined, followed by the addition of unique elements that bring functional enhancement such as mechanical strengthening of the wire.

We approached the internal matrix reinforcements using the Cu-Sn-Zn and Cu-Sn-In ternary bronze alloy matrices. After Nb₃Sn phase synthesis, these ternary bronze alloy matrices were transformed into（Cu, Zn）or（Cu, In）solid solutions having much higher mechanical strength. J_c degradation due to the transverse compressive stress on the internal matrix reinforced Nb₃Sn multifilamentary wire was evaluated. No J_c degradation was observed at approximately 100 and 150 MPa, which values were much higher than the conventional bronze processed Nb₃Sn wire. We found that the internal matrix reinforcement was effective for suppressing J_c degradation due to transverse compressive stress.

The Cu-Nb/Nb₃Sn wires have much higher superconducting properties under large mechanical stresses compared to conventional Cu/Nb₃Sn wires. In the developments of the Cu-Nb/Nb₃Sn Rutherford cables for 25 T cryogen-free superconducting magnet with Tohoku University, we succeeded in improving both superconducting performance and mechanical properties by pre-bending treatment using the React-and-Wind（R&W）method. Subsequently, we have made many prototypes of Cu-Nb/Nb₃Sn wires that satisfy the properties required for various Nb₃Sn coil applications. As a result, we established technologies related to Cu-Nb/Nb₃Sn wires such as higher strength, higher critical current density, rectangular shape, enamel coating, thinner wires for small radius bending, and stranded cables. We also confirmed the effectiveness of Cu-Nb/Nb₃Sn wires not only in the R&W method but also in the W&R method. This paper describes the development progress and future prospects of Cu-Nb/Nb₃Sn wires.

We have been conducting research and development of the DC induction heating device of aluminum billet using HTS magnets. In this R&D, following the development of main components such as the HTS magnet system, the heating control system and the mechanism for grasping and rotating the aluminum billet, the demonstration device for 400 kW-class billet heater was developed and the heating power of over 400 kW was demonstrated. In this study, as the final step of the R&D, we conducted a continuous repetitive heating test and evaluation of the electromagnetic and mechanical influence due to the heating operation on the HTS coil.

It was demonstrated that the continuous repetitive heating of 90 billets（more than two hours）with the rated power was possible. The temperature increase and the behavior of mechanical stress of the HTS coil during the continuous heating operation were evaluated.

It was confirmed that the soundness of the HTS coil through the continuous repetitive heating was not compromised.

Two muon experiments, which require extremely homogeneous magnetic fields, are under preparations in J-PARC. One of the experiments is the MuSEUM（Muonium Spectroscopy Experiment Using Microwave）experiment that requires＋/-0.1 ppm homogeneity in a spheroidal volume of 20 cm in diameter and 30 cm in length. To confirm that such an extremely homogeneous magnetic field can be obtained in a whole-body MRI magnet, intensive shimming tests were conducted using a shimming calculation based on TSVD of linear algebra with a passive shimming structure. In the first shimming test, we found that small shim-piece unit is necessary, and in the second test an extremely homogeneous magnetic field was realized with Ni shim plates, the magnetic moment of which is 1/6 of the ordinal Fe shim plates of MRI magnetic field. This result confirms that an extremely homogeneous magnetic field can be realized for the experiment.