Fully transposed braids for the cable-in-conduit superconductors

One of the prototype 40 kA superconductors developed for coils of the European Fusion Project uses a fully transposed braid as subcable. The new powdered braiding machine developed at ABB for this purpose is described. The operation limits and potential of this kind of machine are discussed. The performances of braided versus stranded superconductors are compared with respect to critical current, AC losses, and mechanical properties. The new braider operated successfully on an industrial basis; the transposition length obtained with the phi =0.93 mm strand was longer than expected, i.e. the braid was less tight than desired. A direct comparison of braided versus stranded cables shows that the braid has better performance with respect to AC losses, and mechanical and hydraulic properties: on the other hand the braid is more sensitive to the thermal contraction of the sheath. The fully transposed braid has been assessed as a satisfactory bundling technique for subcables of large pulsed superconductors.<
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