Microphonics compensation with a FPGA based RF control system at the S-DALINAC

The high Q of the superconducting 3 GHz cavities of the S-DALINAC in combination with microphonic perturbations leads to permanent fluctuations in amplitude and phase of the accelerating field. These fluctuations increase the energy spread of the beam which has to be compensated by a low level RF control system. To meet the required stability the existing analog control system has to be replaced by a digital one. The digital signal processing is done in a FPGA which allows for different control algorithms. Superconducting cavities are operated in a self-excited loop whereas a generator driven resonator is used for normalconducting cavities. The implementation of these algorithms, measurements for characterization of microphonics, and latest results using the control algorithms with a prototype are presented. Furthermore we report on the features of the improved FPGA board revision. These include real time digital readout at full sampling rate which allows extensive diagnostics