Investigation of the correlation between the electrical contact resistance and the contact area of mechanical lap joint fabricated with high-temperature superconducting tapes using X-ray microtomography

A mechanical lap joint fabricated with high-temperature superconducting (HTS) tapes is proposed for the application to joint-winding in HTS magnets for fusion reactors. The applicability of the joint has been validated, however, it could not be guaranteed because the joint resistance is unpredictable before the entire conductor is cooled and energized. Identifying the factors that affect the joint resistance is necessary to develop a method to predict this parameter at room temperature. In this report, we evaluated the correlation between the electrical resistance of contact interfaces (contact resistance) and the contact area observed using X-ray computer tomography scan (observed contact area), and discussed appropriate techniques for this prediction. A total of 40 mechanical lap joint samples were prepared. The observed contact areas were segmented from cross-sectional images of contact interfaces using a graph cut image segmentation, while the contact resistances were calculated from measured joint resistances. The correlation indicated that the prediction of contact resistance is more precise when base on the observed contact area compared to the conventional method using the nominal contact area. However, some of dispersive contact resistivity still remained due to inhomogeneous distribution of fine-structure on contact interface.