Design of a VXI module for beam phase and energy measurements for LEDA

Beam diagnostics systems being designed for the Low Energy Demonstrator Accelerator (LEDA) at Los Alamos include beam synchronous-phase and beam energy measurements. The LEDA machine will utilize an RFQ front end operating at 350 MHz, followed by several 700-MHz DTL accelerating structures. Signals from cavity-field probes and beam image-current probes will be down-converted to 2 MHz for phase measurement in VXI modules. Each 2-MHz signal is sampled at 8 MHz with a 12-bit ADC and the resultant data stream is converted into I and Q components which update at a 2-MHz rate. The I and Q signals are then converted to a relative phase measurement. Each VXI module will contain four channels of phase measurement hardware which allow for two channels of differential-phase measurement. Low-noise AGC circuits will accommodate signal variations over a 64 dB dynamic range. An on-board calibration system provides a system absolute accuracy of ±1 degree. DSP filtering allows 200-kHz bandwidth measurements to be made with a resolution of <0.1 degrees over a dynamic range of 46 dB