Niobium-Thorium Eutectic Alloy as a High-Field, High-Current Superconductor

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Abstract
Niobium‐thorium eutectic alloys having fine acicular microstructures were produced by fast cooling from a vacuum melt. Although the solidified material was normal, continuity between the superconducting niobium‐rich phase, which was essentially pure niobium, was attained by plastic deformation at room temperature. The resulting wire was tested for critical current at 4.2°K, in transverse magnetic fields up to 82.5 kG; at the highest field, critical current densities of slightly more than 104 A per square centimeter were observed. The critical current density was independent of applied field from 20 kG to the highest field used; the level of critical current density depended on diameter in a manner which suggested dependence on cold work. It was concluded that the cold work had reduced the thickness of the needles of niobium below the superconducting penetration depth, and had brought them sufficiently close together to allow the superconducting correlation to interconnect the niobium, in the manner suggested by Cooper; furthermore, the constant critical current region may possibly extend to considerably higher fields.