CRITICAL CURRENTS IN ROEBEL ASSEMBLED COATED CONDUCTORS (RACC)

ROEBEL-type assembling of coated conductors (CC) has recently been introduced as a practicable method to prepare high current flat cables from CC in a low AC loss structure with the feature of fully transposed strands. Up to now we have prepared and analyzed four such RACC cables with 11-16 strands with quite different properties, using two different industrial CC-tapes, SuperPower MOCVD-CC and THEVA TCE-CC. Compared to the sum of single-strand I, values all cables show a current degradation of about 30% or more. The reason can be attributed to the quite inhomogeneous and significantly high self field. The quality of the CC, in particular the homogeneity of the superconducting layer, the amount of applied stabilisation and the feed-in-lengths of the currents, determines the maximum achievable transport current. We present investigations on the conductor homogeneity and transport currents, the influence of strand punching on the strand currents and correlate the cable properties with modelled self field effects in the cables. Main goal of the actual work is to study possibilities of interstrand connections which serve for current redistribution, but have to be balanced against raising coupling losses.