Numerical Study on Silver Diffusion Joints of Coated Conductors by Finite-Element Method
Given the length limitations of commercial coated conductors, joint is very important for their practical applications. Silver diffusion joints are regarded to be promising in the superconducting applications without operation in persistent current mode. This paper presents a 3-D numerical model of silver diffusion joints. The current distributions in the contact layers and their effect on the joint resistance are systematically studied by varying silver layer thickness, length, and width of contact area. It is investigated that the width of the contact area has an inverse proportion to the simulated joint resistances in the range of 2-12 mm like a normal conductor. However, the relationship between the contact length and the simulated joint resistance has an evident deviation from the inverse proportion, because the current distribution in silver layers is highly nonuniform and gives rise to a smaller “silver usage ratio” when the contact length is longer. Based on the hypothesis that the sheet resistivity of ReBCO-Ag and Ag-Ag interfaces is uniformly distributed and is affected by the “silver usage ratio” to the same extent as the bulk resistance of the silver layers, the joint resistances derived from our model are in good agreement with the experimental results.