Nowadays Nb₃Sn wires are being widely used as one of the key materials in advanced science and technology, with various applications such as NMR, fusion and cryogen-free superconducting magnets. In this article, at first microstructures and fundamental aspects as well as the effect of additional elements in Nb₃Sn are outlined. Intrinsic superconducting performances, e.g. T_c and B_c2, are quite sensitive to the stoichiometry of the Sn concentration. A small amount of Ti and Ta doping is much effective for the increase of B_c2 in Nb₃Sn. The effect of Cu on the enhancement of Nb₃Sn synthesis has yielded a significant breakthrough for the industrial production of the wires. At present the bronze process and internal Sn process are the twin major fabrication techniques of Nb₃Sn wires. The recent status of both processes is reviewed in this article. Pronounced progress has been achieved in the performance of Nb₃Sn wires fabricated through both techniques. Although just half a century has passed since the first fabrication of Nb₃Sn wire, further progress in Nb₃Sn technology may be expected like the proverb saying “Fresh water still comes out from an old spring”.

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In photovoltaic (PV) and wind turbine (WT) power generation, which are typical examples of clean power, the amount of power generated changes rapidly and constantly according to the stochastic weather conditions. In order to ensure a high-quality power supply, including constant voltage and current, it is necessary to compensate for the power fluctuations. A system combining fuel cells (FCs), which can generate power for long periods of time, and a superconducting magnetic energy storage (SMES) system, which can produce large amounts of power quickly, can potentially function to compensate the power fluctuations all the time. In this paper, since WT power is resolved into trend and fluctuating components, the former is provided by FCs, and the latter is provided by the SMES system. The trend components are predicted using a Kalman filter, which describes the state-space model for WT power generation. Since the SMES system cost is very high, it is important to optimize the compensation capacity of SMES in the combined system. We found that the trend prediction method, a modification of the Kalman filter, allows us to optimize the SMES capacity.

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The Ring Trap 1 (RT-1) device produces a magnetospheric configuration for the confinement of a high-β plasma with a Bi-2223 high-temperature superconducting magnet. Here we report the results of emergency demagnetization of the superconducting coil, where we could not connect current leads, temperature measurement connectors, and connectors for a persistent-current switch (PCS) heater to the coil. The spontaneous warming of the coil caused a rise in the flux-flow resistance of the superconducting coil, and the persistent current slowly decreased as coil resistance increased. Approximately 98% of the total stored magnetic energy was safely released before the quenching of the PCS, and there was no substantial damage to the coil.

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