Investigation on I C Degradation of MgB2 Rutherford Cables by Deformation During Cabling Process

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MgB2 superconductors are promising candidates for application to devices such as Superconducting Magnetic Energy Storage, and generators. To apply MgB2 conductors to such devices, the current capacity of a conductor must be in the kilo-ampere range. Meanwhile, because the current capacity of a MgB2 conductor is typically approximately 100 A at 5 T and 4.2 K, multiple stranded cables are required. One candidate is the Rutherford-type cable. During the fabrication of Rutherford cables, strands are deformed by large bending strains at edge corners and indented at flat parts from the pressure of roller dies to maintain the cable shape. It is important to understand how critical current degrades during the fabrication of Rutherford-type cables. To optimize the strand transposition length, three types of Rutherford cables were fabricated and the critical current degradation depending on bending and indented strains was measured. Moreover, to investigate the degradation, inner structures of the strands were observed using micro-focused X-ray computed tomography and an electron probe micro analyzer.