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Abstract. The FAIR project was initiated to build an international accelerator and experimental facility for basic research activities in various fields of modern physics. The core component of the project will be the SIS100 heavy ion accelerator, producing heavy ion beams of uniquely high intensities and qualities. The superconducting main quadrupoles and corrector magnets are assembled within complex quadrupole doublet modules (QDMs), combining two superconducting quadrupole (focusing and defocusing), sextupole and steering magnets in one cryostat. In addition a cryo-catcher, a beam position monitor and a cold beam pipe will be integrated. In accordance with the magnet lattice structure, the QDM series for the SIS100 consists of four main families composed of eleven different configurations. The common technical feature of all configurations is a sophisticated common girder structure, mechanically integrating all functional components in one cold mass and being suspended in a corresponding cryostat system. The requirements to position preservation during thermal cycling are to be fulfilled by a precise and stable support of the functional elements, as well as by a reliable, reproducible and stable cold mass suspension system. The main design aspects of the QDMs will be discussed as a result of these requirements.

Dynamic processes in a window-frame dipole with superconducting windings and a cold, laminated iron yoke have been investigated experimentally at JINR (Dubna, Russia), and theoretically at GSI (Darmstadt, Germany). The main aim of these investigations was a reduction of energy losses in the yoke during ramping. These losses are produced mainly by energy dissipation due to eddy currents and hysteresis effects in the laminations. Both effects were investigated theoretically. As a result, special end blocks were proposed to reduce eddy current losses. For eddy currents simulation we used a model developed at GSI and St. Petersburg State Polytechnical University (Russia). This model is based on an integro-differential approach to eddy currents in laminated structures and a volume integral method for the magnetization vector in ferromagnetic objects. To test this model a series of experiments were performed at GSI on a normalconducting Heavy Ion Synchrotron dipole magnet. The magnetic field in the aperture of this magnet was controlled with a point coil during the current ramping in the winding. The same transient processes were simulated using software, developed on the basis of the integro-differential method. The theoretical calculations were in reasonable agreement with the measurements.Index Terms-Ion beam applications, magnetic fields, magnets, superconducting accelerator magnets.

The conceptual design of the magnetic system of the SIS100 synchrotron was described in the Technical Design Report of the FAIR project. The accelerator superconducting magnetic system consists of different types of modules containing the main dipole and quadrupole magnets, different corrector magnets and special units like beam position monitors, particle catchers and others. The first set of full size dipole and quadrupole prototypes was manufactured. Their tests are continued. The final engineering design is carried out by the GSI/JINR collaboration addresses all technical issues of the system units for which adequate solution will be defined. Special designs have to be worked out for the switchingmodules needed for beam injection, extraction and transfer. Many special issues are connected with the quadrupole modules. There are 84 such modules of about 4 m long each in the accelerator ring. The essential features of the modules are discussed. General status of the system engineering design is presented.