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Olsen, J.

Paper Title Page
WPPB40 LCLS Beam-Position Monitor Data Acquisition System 478
  • R. Akre, R. G. Johnson, K. D. Kotturi, P. Krejcik, E. Medvedko, J. Olsen, S. Smith, T. Straumann
    SLAC, Menlo Park, California
  In order to determine the transversal LCLS beam position from the signals induced by the beam in four stripline pickup electrodes, the BPM electronics have to process four concurrent short RF bursts with a dynamic range > 60dB. An analog front end conditions the signals for subsequent acquisition with a waveform digitizer and also provides a calibration tone that can be injected into the system in order to compensate for gain variations and drift. Timing of the calibration pulser and switches, as well as control of various programmable attenuators, is provided by an FPGA. Because no COTS waveform digitizer with the desired performance (>14bit, ≥119MSPS) was available, the PAD digitizer (see separate contribution WPPB39) was selected. It turned out that the combination of a waveform digitizer with a low-end embedded CPU running a real-time OS (RTEMS) and control system (EPICS) is extremely flexible and could very easily be customized for our application. However, in order to meet the BPM real-time needs (readings in < 1ms), a second Ethernet interface was added to the PAD so that waveforms can be shipped, circumventing the ordinary TCP/IP stack on a dedicated link.