This report deals with the design of the high field rapidly-cycling super-conducting dipoles needed for SIS300 synchrotron of the FAIR facility at GSI. The main results of the R&D activities, developed for supporting the design choices, are presented elsewhere. The characteristics of the dipole come from the requirement of the SIS300. The present lattice design includes 48 long dipoles with magnetic length 7.757 m and 12 short dipoles with magnetic length 3.879 m. The coils have two main

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... s: they are curved (the corresponding sagitta is 112.8 mm for long dipoles), and they are fast ramped (for a superconducting magnet). Both these characteristics demanded a challenging R&D, aimed at the development of the required low loss conductor, a robust design with respect to fatigue issues and a suitable winding technology. The Italian National Institute of Nuclear Physics (INFN) performed this R&D. A project, called DISCORAP ('Dipoli SuperCOnduttori RApidamente Pulsati')', was developed in accordance with a specific INFN-FAIR Memorandum of Understanding signed by both institutions in December 2006. As output of this project a complete cold mass model of the short dipole was built and preliminary tested. The cold mass was integrated into a horizontal cryostat and presently activities are ongoing for testing the magnet at GSI cryogenic facilities.