Electromagnetic Properties of Lap-Joint and Its Influences on the Conductor Test Data

A joint between superconducting cables is one of key elements in a large-scale magnet. Joint-resistance-induced nonuniform current distribution has been reported. The mechanism of this phenomenon is quite simple. The cable consists of the twisted superconducting strands. Therefore, in the DC condition, the current distribution is governed by the nonuniformity of individual sub-joint-resistances between twisted strands in different legs; those are mainly determined by the joint configuration. When one strand carries larger current and it saturates at the critical current, flux-flow resistance occurs. That nonlinear resistance functions as a current regulator. Once the current saturates in one strand, surplus current must go through other strands. Apparent critical current, n-value and current sharing temperature (Tcs) of the CICC are important parameters for magnet design. However these have been reported to be degraded from the expected values predicted from the strand performances. We analyzed the apparent evolution of flux-flow voltage along the cable considering the current nonuniformity due to the lap-joint quality