Evaluation of PbMo_6S_8 Coils(Low-T_c Superconducting Materials Research)

Small 3-layer coils with two kinds of mandrels (Al_2O_3 and MgO) have been fabricated using Chevrel-phase PbMo_6S_8(PMS) superconducting wires prepared by a powder process and their J_c evaluations have been carried out. An excellent J_c of 3.0x10^4A/cm^2 at B=12T was obtained for the coil with a MgO mandrel, which corresponded to 84% of the best J_c for a similar short wire. In the case of an Al_2O_3 mandrel, the J_c was degraded to 60% of the value. The evaluations of thermal expansion coefficient and I_c-strain property on PMS wires have been also carried out. The J_c degradation of the coils due to the tensile strain, which is induced in the wire by the mandrels during cooling process, has been estimated. In consequence, the origin of J_c degradation for the small coils was found to be strain applied from mandrels in the cooling process