2012 年 23 巻 3+4 号 p. 19-21
High temperature superconducting current leads have been prepared by the TFA-MOD processed YBCO tapes. The YBCO tape is 5 mm in width, 190 mm in length and about 130 µm in overall thickness. The YBCO superconducting layer with 1.5 µm in thickness is formed on oxide buffer layers on Hastelloy substrate tape. Transport current is supplied through Ag layer deposited on YBCO layers. A current lead unit is composed of twenty YBCO tapes soldered to Cu caps at both of ends and a GFRP board. The twenty tapes are arrayed in five rows of stacked four tapes in parallel. The transport current of ten current lead units ranges from 1.5 kA to 2.5 kA at 77 K. The heat leakage of the current lead unit with 150 mm in length between 77 K and 4.2 K is estimated to be 281 mW. Therefore, the heat load at 2 kA corresponds to 140 mW/kA, which is around one order of magnitude smaller than that of conventional current lead. The small heat leakage results from high current performance and low thermal conductivity in the present HTS current lead.