冷凍機直冷式超電導マグネット用Bi-2212酸化物電流リード

抄録

We have developed a Bi₂Sr₂CaCu₂O_8+x(Bi-2212) current lead for a 10T NbTi/Nb₃Sn magnet cooled by a cryocooler. The Bi-2212 bulk used in the lead was fabricated by a floating zone melting method with a CO₂ laser. The grain-aligned microstructure along the longitudinal direction of the bulk, exhibited better magnetic field dependence of the critical current density J_c below 50K. This implies that the Bi-2212 lead is useful even in a high leakage field, when the high temperature end is connected to the 50K stage of a cryocooler. Moreover, an inner flexible copper portion was designed to reduce the thermal contraction difference. In the 10T magnet, a pair of these leads successfully transported 130 Amp. at a leakage field of 0.35T, which corresponded to a 10T field. The heat load to the 4K stage was 45mW, which was 1/10 of conventional Cu leads and was enough small for a cryocooler.