Speaker
Description
Superconducting wires undergo large plastic deformation during manufacturing of Rutherford cables, especially at the cable edges. Previous studies on Restack Rod Process (RRP) Nb$_3$Sn wires have shown that the position of the strands in the cable and the orientation of the subelement stack, with respect to the main rolling direction during cabling, are affecting the amount of plastic deformation to which individual subelements are subjected. Subelements with damaged niobium diffusion barriers lead to tin diffusion into the copper matrix during heat treatment and a reduction of the residual resistivity ratio (RRR). For the High-Luminosity Upgrade of the Large Hadron Collider, more than one hundred Rutherford cables were manufactured at Lawrence Berkeley National Laboratory. In-line imaging of all four sides of the cables were acquired to assess cabling deformation and more by measuring the dimensions of all facets on the minor and major edges. RRR measurements at the cable-edge kinks and the straight sections of individual extracted strands were also performed to assess cabling-induced performance degradation. This study is building on this historical data to advance our understanding of the relationship between facet size and RRR degradation in Nb$_3$Sn RRP wires during cabling. Cross-sectional metallography at the kink of extracted strands is used to study differences in microstructures after heat treatment for wires with different RRR values and facet sizes.
This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, through the US Magnet Development Program. The work performed at Lawrence Berkeley National Laboratory was supported by the Office of High Energy and Nuclear Physics, U. S. Department of Energy, under contract No. DE-AC02-05CH11231.
