Digital BPM Systems for Hadron Accelerators

The CERN Proton Synchrotron has been fitted with a new trajectory measurement system (TMS). Analogue signals from forty beam position monitors are digitized at 125MS/s, and then further treated entirely in the digital domain to derive the positions of all individual particle bunches on the fly. Large FPGAs handle all digital processing. The system fits in fourteen plug-in modules distributed over three half-width cPCI crates. Data are stored in circular buffers of large enough size to keep a fewseconds-worth of position data. Multiple clients can then request selected portions of the data, possibly representing many thousands of consecutive turns, for display on operator consoles. The system uses digital phase-locked loops to derive its beamlocked timing reference. Programmable state machines, driven by accelerator timing pulses and information from the accelerator control system, direct the order of operations. The cPCI crates are connected to a standard Linux computer by means of a private Gigabit Ethernet segment. Dedicated server software, running under Linux, knits the system into a coherent whole.