Electromagnetic Design Study for a Large Bore 15T Superconducting Dipole Magnet

In the framework of research and development (R&D) activities at CERN the Next European Dipole (NED) program is one which is to the development of a high-field dipole magnet using Nb_3Sn superconductors. Part of the NED activities is a design study of different possible dipole configurations which is shared amongst the collaborating institutes. This thesis covers the electromagnetic design study of an 88 mm large bore superconducting 15 T dipole magnet with a coil cross section in cos-theta-layer design. Based on analytically describable geometries the sources of multipole errors are studied and elementary estimations of the magnet are carried out, e.g., the required amount of superconductors or the influence of the iron yoke thickness on the field quality. The magnet cross section for NED is optimized by means of the CERN field computation program ROXIE. The preliminary NED design serves as starting point for the coil cross section optimization with respect to field quality and a radial positioning of the conductor blocks. Due to the high field of magnetic induction, the surrounding iron yoke saturates for high transport currents and the multipole errors vary with excitation. In order to reduce the variation, modifications of the iron yoke shape are studied, like, e.g., holes punched into the yoke laminations, a change of the outer yoke contour or an inner contour of elliptical shape. For an elliptically shaped inner iron yoke contour the coil cross section is again optimized resulting in the Reference Design V. 2 for the NED collaboration. The persistent current induced field errors are estimated for the present design and NED cable. Based on these results different compensation methods are investigated including ferromagnetic shims inside the cables, mounted on the cold bore tube or on the copper wedges.