Accurate calculation of fringe fields in the LHC main dipoles

The ROXIE program developed at CERN for the design and optimization. of the superconducting LHC magnets has been recently extended in a collaboration with the University of Stuttgart, Germany, with a field computation method based on the coupling between the boundary element (BEM) and the finite ele ment (FEM) technique. This avoids the meshing of the coils and the air regi ons, and avoids the artificial far field boundary conditions. The method is therefore specially suited for the accurate calculation of fields in the s uperconducting magnets in which the field is dominated by the coil. We will present the fringe field calculations in both 2d and 3d geometries to eval uate the effect of connections and the cryostat on the field quality and th e flux density to which auxiliary bus-bars are exposed.