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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.

The low level rf system for the superconducting Darmstadt electron linear accelerator (S-DALINAC) developed 20 years ago and operating since converts the 3 GHz signals from the cavities down to the baseband and not to an intermediate frequency. While designing the new, digital rf control system this concept was kept: the rf module does the I=Q and amplitude modulation/demodulation while the low frequency board, housing an field programmable gate array analyzes and processes the signals. Recently, the flexibility of this concept was realized: By replacing the modulator/demodulators on the rf module, cavities operating at frequencies other than the one of the S-DALINAC can be controlled with only minor modifications: A 6 GHz version, needed for a harmonic bunching system at the S-DALINAC and a 324 MHz solution to be used on a room temperature cavity at GSI, are currently under design. This paper reviews the concept of the digital low level rf control loops in detail and reports on the results gained during first operation with a superconducting cavity.

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The accelerating field in superconducting cavities has to be stabilized in amplitude and phase by a radio-frequency (rf) control system. Because of their high loaded quality factor superconducting cavities are very susceptible for microphonics. To meet the increased requirements with respect to accuracy, availability, and diagnostics, the previous analog rf control system of the superconducting Darmstadt electron linear accelerator S-DALINAC has been replaced by a digital rf control system. The new hardware consists of two components: An rf module that converts the signal from the cavity down to the base-band and a field-programmable gate array board including a soft CPU that carries out the signal processing steps of the control algorithm. Different algorithms are used for normal-conducting and superconducting cavities. To improve the availability of the control system, techniques for automatic firmware and software deployment have been implemented. Extensive diagnostic features provide the operator with additional information. The architecture of the rf control system as well as the functionality of its components will be presented along with measurements that characterize the performance of the system, yielding, e.g., an amplitude stabilization down to ðÁA=AÞ rms ¼ 7  10 À5 and a phase stabilization of ðÁÞ rms ¼ 0:8 for superconducting cavities.