HTS Dipole Magnet for a Particle Accelerator Using a Twisted Stacked Cable

High-T_c superconducting (HTS) dipole magnets are expected to be used in the upgrade of existing particle accelerators. In the framework of EuCARD-2 project, a new dipole-generating field between 17 and 20 T is under consideration with an HTS insert providing 5 T. This has to provide a good field quality at two-thirds of 40-mm beam aperture. The HTS stacked cable is the simplest way to acquire the large current and a strong mechanical cable. A twist for a half-turn in the magnet ends partially transposes the stacked tapes and improves the current distribution. However, the twisted stacked cable exposes the ReBCO tape to magnetic fields perpendicular to their wide face, where the engineering current density J_e is lower. In addition, the different strength and direction of forces cause shear stress between the tapes. The HTS twisted stacked insert is designed with a 4 × 4-mm block-coil stacked with 4-mm-wide tape. The 46-turns of stacked cable, which is almost aligned to the background field, achieve a 5 T with the required field quality. The 3-D magnet ends are designed with the racetrack and flared-ends coils. It consists of six double pancakes. One of the mechanical conditions in the coil-ends, whose block-coil is divided into four tapes, has been analyzed with the Fresca2 LTS outsert. The HTS insert is able to withstand forces on its own.