FABRICATION AND EVALUATION OF SMALL COILS USING PBMO6S8 WIRES

Small three-layer coils with two kinds of mandrels (Al2O3 and MgO) were fabricated using Chevrel-phase PbMo6S8 (PMS) superconducting wires prepared by a powder process. J(c) evaluations were carried out on these coils. An excellent J(c) of 3.0 x 10(4) A cm-2 at B = 12 T was obtained for the coil with a MgO mandrel, which corresponded to 84% of the best J(c) for the same short wire. In the case of the Al2O3 mandrel, the J(c) was degraded to 60% of this value. The thermal expansion coefficient and I(c)-strain property of the PMS wires were also determined. The J(c) degradation of the coils due to the tensile strain induced in the wire by the mandrels during the cooling process was estimated. As a consequence, the origin of J(c) degradation for the small coils was found to be the strain applied from mandrels during the cooling process.