Study of Effects of Deformation in Nb3Sn Multifilamentary Strands

In the process that leads a flawless Nb₃Sn round strand to become part of a Rutherford cable first, and of a coil next, the same cabling process affects strands of different kinds in different ways, from filament shearing to subelement merging to composite decoupling. Due to plastic deformation, after cabling the filament size distributions in a strand usually change. The average filament size typically increases, as does the width of the distribution. This is consistent with the low field transport current of strands in cables being typically lower and less reproducible than for round strands [E. Barzi et al., RRP Nb₃Sn Strand Studies for LARP, presented at the Applied Superconductivity Conference, 1MK07, unpublished]. To better understand the role of filament size in instabilities and to simulate cabling deformations, strands to be used in cables can be tested by rolling them down to decreasing sizes to cover an ample range of relative deformations. A procedure is herein proposed that uses both microscopic analysis and macroscopic measurements of material properties to study the effects of deformation.