The fusion power density produced in a tokamak is proportional to its magnetic field strength to the fourth power. Second-generation high temperature superconductor (2G HTS) wires demonstrate remarkable engineering current density (averaged over the full wire), JE, at very high magnetic fields, driving progress in fusion and other applications. The key challenge for HTS wires has been to offer an acceptable combination of high and consistent superconducting performance in high magnetic fields, high volume supply, and low price. Here we report a very high and reproducible JE in practical HTS wires based on a simple YBa2Cu3O7 (YBCO) superconductor formulation with Y2O3 nanoparticles, which have been delivered in just nine months to a commercial fusion customer in the largest-volume order the HTS industry has seen to date. We demonstrate a novel YBCO superconductor formulation without the c-axis correlated nano-columnar defects that are widely believed to be prerequisite for high in-field performance. The simplicity of this new formulation allows robust and scalable manufacturing, providing, for the first time, large volumes of consistently high performance wire, and the economies of scale necessary to lower HTS wire prices to a level acceptable for fusion and ultimately for the widespread commercial adoption of HTS.

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LiFeAs is one of the iron-based superconductors having multiple gaps with the possible sign reversal. To clarify how those novel natures affect the energy dissipation of magnetic vortices, we investigated the microwave surface impedance of LiFeAs single crystals under finite magnetic fields. The flux-flow resistivity enhanced rapidly at low magnetic fields, which is similar to the case of MgB2. This is probably the consequence of the multiple-gap nature and the gap anisotoropy. This suggest that the sign-reversal is not important for the flux-flow even for multiple-gap superconductors. As for the electronic state, the vortex core of LiFeAs turned out to be "moderately clean". Furthermore, the mean free path inside the vortex core was much shorter than that outside, and was close to the core radius. These results strongly suggest a process specific to the core boundary is important for a scattering mechanism inside the vortex core.

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Method of synthesis of high-quality thin films of Fe chalcogenides, Fe(Te,Se) and FeSe are studied. By investigating the correlation between Tc and structural parameters, it is concluded that a compressive strain is introduced on the films on CaF2 substrate, which leads to an increase of Tc than on oxide substrates. Properties both in the normal state and in the superconducting state are measured. Results are discussed in terms of the possibility of further increasing Tc of this material.