SLAC, Menlo Park, California, USA
CERN, Geneva, Switzerland
An ultrafast 4GSa/s transverse feedback processor has been developed for proof-of-concept studies of feedback control of e-cloud driven and transverse mode coupled intra-bunch instabilities in the CERN SPS. This system consists of a high-speed ADC on the front end and equally fast DAC on the back end. All control and signal processing is implemented in FPGA logic. This system is capable of taking up to 16 sample slices across a single SPS bunch and processing each slice individually within a reconfigurable signal processor. This demonstrator system is a rapidly developed prototype, consisting of both commercial and custom-design components. It can stabilize the motion of a single particle bunch using closed loop feedback. The system can also run open loop as a high-speed arbitrary waveform generator and contains diagnostic features including a special ADC snapshot capture memory. This paper describes the overall system, the feedback processor and focuses on the hardware architecture, design and implementation.
SLAC, Menlo Park, California, USA
CERN, Geneva, Switzerland
We present the architecture and implementation overview of a digital signal processing system developed to study control of Electron-Cloud and Transverse Mode coupling instabilities in the CERN SPS. The system is based on a reconfigurable processing architecture which samples vertical bunch motion and applies correction signals at a 4 GS/s rate, allowing 16 samples across a single 5 ns SPS RF bucket. The system requires wideband beam pickups and a vertical kicker structure with GHz bandwidth. This demonstration system implements a general purpose 16 tap FIR control filter for each sample. We present results from SPS machine studies showing the impact of wideband feedback to excite/damp internal modes of vertical motion as well as stabilize an unstable beam. These results highlight the challenges of intra-bunch feedback and show proof of principle feasibility of the architecture.
