Numerical Study on Simplified Resistive Joints of Coated Conductors: Is There a Lower Limit of the Joint Resistance?
In this study, three-dimensional (3-D) numerical models of resistive joints for ReBCO coated conductors are established in the commercial finite element analysis software COMSOL Multiphysics 5.0. In this simplified model, only two ReBCO layers and one/two “connection” layer(s) (i.e., the resistive interlayer(s) sandwiched by two ReBCO layers) are considered. 3-D power-law E–J relationship (where J is the current density, E is the electric field intensity) is employed for superconducting layer and an isotropic bulk resistance is set for the connection layer(s). The interfacial resistances are taken into account by introducing boundary weak contributions. The joint resistance exhibited a non-uniform relationship with the geometry of the joining area. And the joint resistance tended to approach to a lower limit value. Silver diffusion joint samples are fabricated and tested to verify the simulation results and a good agreement is obtained. The above phenomenon is attributed to the highly non-uniform current distribution in the ReBCO layers and therefore in the connection layers. By our simulation, it is found that the criterion value of overlap length (the length of joining area) corresponding to the lower limit of joint resistance is highly related to the resistivity of the connection layer.