HTS current lead units prepared by the TFA–MOD processed YBCO coated conductors

Abstract

Two superconducting current lead units have been prepared using ten coated conductors of the Tri-Fluoro-Acetate – Metal Organic Deposition (TFA–MOD) processed Y1Ba2Cu3O7−δ (YBCO) coated conductors with critical current (Ic) of about 170A at 77K in self-field. The coated conductors are 5mm in width, 190mm in length and about 120μm in overall thickness. The 1.5μm thick superconducting YBCO layer was synthesized through the TFA–MOD process on Hastelloy™ C-276 substrate tape with two buffer oxide layers of Gd2Zr2O7 and CeO2. The five YBCO coated conductors are attached on a 1mm thick Glass Fiber Reinforced Plastics (GFRP) board and soldered to Cu caps at the both ends. We prepared two 500A-class current lead units.The DC transport current of 800A was stably applied at 77K without any voltage generation in all coated conductors. The voltage between both Cu caps linearly increased with increasing the applied current, and was about 350μV at 500A in both current lead units. According to the estimated values of the heat leakage from 77K to 4.2K, the heat leakage for the current lead unit was 46.5mW. We successfully attained reduction of the heat leakage because of improvement of the transport current performance (Ic), a thinner Ag layer of YBCO coated conductor and usage of the GFRP board for reinforcement instead of a stainless steel board used in the previous study.The DC transport current of 1400A was stably applied when the two current lead units were joined in parallel. The sum of the heat leakages from 77K to 4.2K for the combined the current lead units was 93mW. In comparison with the conventional Cu current leads by gas-cooling, it could be noted that the heat leakage of the current lead is about one order of magnitude smaller than that of the Cu current lead.