Development of a Roebel-Cable-Based $\cos\vartheta$ Dipole: Design and Windability of Magnet Ends

In the scope of the Future Circular Collider, work package 10, i.e., “Future Magnets,” of the EuCARD2 project aims at investigating accelerator quality magnets made of high-temperature superconductors. This paper deals with development of a $\cos\vartheta$ dipole relying on Roebel cable technology. In the first part, we present in detail the design of the dipole: the magnet generates 5 T in stand-alone mode with an overall current density of 684 A/mm 2 . When operating in a background field of 13 T, an extra field of 2 T can be provided by the $\cos\vartheta$ insert due to mechanical limitations. A field increase up to 2.5 T is conceivable, providing the addition of inner shell reinforcement that would reduce the magnet aperture from 40 to 30 mm. In the second part, winding tests of dummy Roebel cable are reported. They demonstrate the challenges stemming from the relative slippage of the cable tapes while winding, which may be overcome by a lengthening of the longitudinal gap of the cable either by an increase of the transposition pitch or a decrease of the number of tapes in the cable. The cable shows a smooth winding behavior along the coil for two different magnet end designs and for its path outward the magnet.