Conceptual design of coaxial multi-layer type CIC for SC magnet of FFHR

An imbalanced current distribution is often observed in cable-in-conduit (CIC) superconductors which are composed of triplet type multi-staged sub-cables, and hence deteriorates the performance of the coils. Since it is very difficult to control homogeneous current distribution in the triplet type CIC, we propose a coaxial multi-layer type CIC to obtain the homogeneous current distribution. We use a circuit model to analyse the current distribution in the coaxial multi-layer CIC. After calculating inductances between adjacent layers in the coaxial multilayer cable, we can derive a generalized formula governing the current distribution as explicit functions of the superconducting cable construction parameters, such as twist pitch, twist direction, layer radius and SC and Cu strands number. We apply the formula to design the coaxial multi-layer CIC for SC magnet of Force Free Helical-type Fusion Reactor (FFHR). We can design the coaxial multi-layer CIC with the homogeneous current distribution, and investigate several SC strand arrangements in the CIC, and optimize the superconducting strand volume.