Relation between contact resistance and twist pitches in superconducting doublets

We prepared sample doublets made of two strands with three different twist pitches (25, 50 and 65 mm). One of the doublets is equally twisted to each other, and the other is a strand twisted in spiral around a straight strand. We measured the contact resistance between the strands in the doublets in liquid helium. Since not only the resistance but also mechanical properties of the strands (applied force to the strands and deformation of the doublet due to the force) were measured, the contact area could be precisely estimated, and then the surface resistance was also evaluated. As a result, the difference between the virgin-contact resistance and the contact resistance with the compressive force applied on the doublets increased when the twist pitch of the doublets became short, and the difference in the shapes of the doublets have an influence on the contact resistance. The obtained results enlarge the database used to simulate an electric circuit model of multi-stranded conductors and to estimate inter-strand coupling losses in the conductors.