Cos- <tex-math notation='TeX'>$\theta$</tex-math> Design of Dipole Inserts Made of REBCO-Roebel or BSCCO-Rutherford Cables

Next generation of dipole magnets with a field higher than 16 T are considered for future particle colliders. To do so, combined-technology magnets, made of Nb-Ti, Nb3Sn and high-temperature superconductor (HTS) materials, have to be developed to reduce the cost of such a magnet. Therefore, in the framework of the European Coordination for Accelerator Research and Development (EuCARD-2) project, many HTS dipole magnet designs have to be investigated to find the most effective design for the HTS insert in a graded magnet. This paper discusses the cos θ option. A 5-T stand-alone configuration of the HTS accelerator magnet (the first goal of EuCARD-2) appears to be achievable, whereas mechanical stress distribution shows that its use as an insert in a graded magnet is very challenging. This paves the way for alternative designs as the so-called slot or motor-like design, which is briefly introduced here.