A digital base-band RF control system

The S-DALINAC is a 130 MeV recirculating electron linac that is operated in CW mode. The analog RF control system of the S-DALINAC has been replaced by a new digital system. The new hardware consists of an RF module and an FPGA board that have been developed in-house. A self-developed CPU implemented in the FPGA executing the control algorithm allows to change the algorithm without time-consuming synthesis. Another micro-controller connects the FPGA board to a standard PC server via CAN bus. This connection is used to adjust control parameters as well as to send commands from the RF control system to the cavity tuner power supplies. The PC runs Linux and an EPICS IOC. The latter is connected to the CAN bus with a device support that uses the SocketCAN network stack included in recent Linux kernels making the IOC independent of the CAN controller hardware. A diagnostic server streams signals from the FPGAs to clients on the network. Clients used for diagnosis include a software oscilloscope as well as a software spectrum analyzer. The parameters of the controllers can be changed with Control System Studio. We will present the architecture of the RF control system as well as the functionality of its components from a control system developer point of view. (authors)