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To expand the application range of high-temperature superconducting (HTS) conductors, the transport characteristics of REBCO coated conductors were evaluated under liquid hydrogen and liquid neon cooling conditions. Although REBCO conductors maintain their superconducting state at the liquid nitrogen temperature of 77 K, their intrinsic performance cannot always be fully exploited in applications involving high current densities and high magnetic fields. Cooling to the 20–30 K temperature range markedly enhances the critical current density, enabling current densities more than an order of magnitude higher than those at 77 K.
Liquid hydrogen is one of the candidate coolants for this temperature range; however, its flammability imposes substantial safety-management requirements. Liquid helium is nonflammable but suffers from high cost, limited availability, and operational constraints. In contrast, liquid neon has a boiling point of approximately 27.1 K and can provide a cryogenic environment comparable to that of liquid hydrogen. As a nonflammable noble gas, it is an attractive coolant for evaluating HTS applications in the 20–30 K temperature range.
A measurement system has been developed to evaluate the V–I characteristics and stability of REBCO coated conductors under liquid neon cooling at approximately 27 K. Prior to the experiments, the cooling
energy required to liquefy 200 cm^3 of neon was estimated from the enthalpy difference between neon gas at 300 K and saturated liquid neon at 27.1 K near atmospheric pressure. The required heat removal was calculated to be approximately 90.5 kJ. Assuming an effective cooling capacity of 5 W, the liquefaction time was estimated to be approximately 5.0 h, indicating that several hours are required for the liquefaction process in liquid neon experiments.
The measurement system is based on an inductive current-excitation method. A sinusoidal current is applied to the primary coil, inducing a transport current in the secondary superconducting loop through electromagnetic induction. The V–I characteristics of the conductor are then obtained from the secondary-side response. This technique enables transport-characteristic evaluation without introducing large currents directly into the superconducting conductor inside the cryostat. In this study, a Fujikura REBCO coated conductor incorporating a BHO-doped EuBCO superconducting layer was employed as the test sample.
The measurement system, liquefaction analysis, comparison between liquid hydrogen and liquid neon cooling experiments, and conductor stability are presented and discussed based on the experimental results.
| Submitters Country | Japan |
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| Are you a student? | Yes |
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