Analysis of magnetization, AC loss, and deff for various internal-Sn based Nb3Sn multifilamentary strands with and without subelement splitting Original Research Article

Magnetization, AC loss, χDC and deff were measured for several designs of rod-in-tube based internal-Sn Nb3Sn type superconducting multifilamentary strands. Two kinds of subelement geometries were used in strand construction. The first had the standard annular Nb/Cu ring surrounding a Sn source; the second was similar but included an internal split intended to reduce magnetization and loss. Strands with 18 and 36 subelements were measured, at strand diameters of 0.5–0.8 mm. Optical, SEM, and EDS measurements were performed on these samples; average radii are reported and physical barrier integrity is found to be good. The magnetizations of these structures were analyzed in terms of a deff parameter, in this case calculated for annular structures. Analytical and numerical results of these calculations are presented. It was found that in general annular structures should be expected to have deff values somewhat larger than the subelement diameter; the value of this enhancement is reported. Also, the effect of subelement splitting on deff and magnetization was calculated. The results of these calculations are compared to the experimentally measured results. Reductions in deff due to subelement splitting are compared to direct, low-field susceptibility measurements. Magnetization values are seen to be nearly uniformly lower in the split subelement strands, and this leads in some but not all cases to significantly lower deff values. Possible reasons for these discrepancies are discussed.