Current transfer length revisited

We constructed a model to estimate analytically the current transfer from a matrix to a superconducting region through a highly resistive barrier layer. Also, a numerical model was formulated in order to study the current transfer when the superconducting region has nonlinear resistivity. Because so far the definition for current transfer length (CTL) has not been well established we propose a definition which introduces a method to determine the CTL corresponding to a chosen criterion. Two possible criteria are suggested. One relates to electric field and the other to current in the superconducting region. As a consequence this paper gives an analytical formula which can be used for example in a short-specimen measurement to determine the disposable measurement area. As examples, the different CTL criteria were computed with different resistivities in the superconductor. Also, analytical and numerical models were compared. The analysis was carried out for the possible general structure of future MgB 2 conductors: superconductor, barrier layer and matrix metal. According to the results, the presented analytical model is a useful tool in determining the current transfer length when the barrier layer contact resistance is at least 25 µΩ mm 2 . Otherwise the presented numerical model must be used.