The experimental studies performed under this contract comprised investigation of two principal approaches to achieving very low levels of ac loss in Nb3Sn produced by the liquid diffusion process:nI. Inhibition of the formation of coarse structured Nb3Sn surface layers.nII. Surface refinement by removal of coarse structured Nb3Sn surface layers.nThe results of these investigations are reported in detail.nIt was found that ac losses increased directly and sensitively with Sn loading, whereas formation of the coarse surface- layer responded limitedly and sluggishly to this parameter. No quantitative correlation was identified between losses and the observed thickness of the coarse structure. Although the effect of coating composition on losses was apparent in some samples, compositional influences tended to be obscured by the predominantly regulatory role of the Sn loading parameter. Nb3Sn formation under "Sn limited" reaction conditions appeared as the only useful guideline as inferred from the data for achievement of low loss NB3Sn product.
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