Composition Profiles in Nb3Sn Diffusion Layers
The utility of Nb3Sn as a practical superconductor has been immensely increased by the solid-state bronze-niobium process  for the production of Nb3Sn because it has enabled the fabrication of practical multifilamentary Nb3Sn magnet conductors for large-scale devices . Current multifilamentary conductors contain 1000 to 100,000 fine filaments, about 2 to 5 μm in diameter; the Nb3Sn layer is grown during a reaction heat treatment at about 700°C after the ductile niobium and bronze have been reduced to the final composite size. Various recent studies have investigated the basic superconducting properties of the composites and the dependence of transition temperature (T c ), upper critical field (H c 2), and critical current density (T c ) on the composite makeup and reaction conditions [3,4]. The superconducting properties of Nb3Sn are strongly sensitive to the precise stress state of the Nb3Sn, the degree to which the Nb3Sn is actually Nb-25 at.% Sn and not off stoichiometry, and the extent to which additional impurity elements are present in the layer. Because of the limited information available about the chemical composition of the 1- to 2-μm-thick layers in multifilamentary Nb3Sn, it is often not clear which of these factors is controlling the superconducting properties.
KeywordsTitanium Quartz Phosphorus Argon Milling
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