Investigation of influences of film resistance and magnetic field on contact resistance in a mechanical lap joint of GdBCO tapes

In order to design a remountable (demountable) high temperature superconducting (HTS) magnet of a fusion reactor, it is necessary to predict joint resistance in a mechanical (electrical) joint of HTS conductors as functions of temperature and magnetic field. Holm contact theory explains that the contact resistance consists of the constriction resistance and the film resistance. The film resistance depends on the thickness of oxide layers on contact surface. In this paper, therefore, relationship between influences of the film resistance and surface roughness of the stabilizing copper layer of a gadolinium barium copper oxide tape was investigated using experimentally evaluated joint resistance. Next, dependencies of contact resistance on the temperature and magnetic field were evaluated using the experimentally obtained joint resistance. Then, a new model of contact resistance was suggested based on the results of current distribution analysis. The contact resistance based on the new model shows good agreement for the test results of a 100-kA class HTS conductor, which demonstrates the validity of the model.