An Automated BPM Characterization System for LEDA*

An automated and highly accurate system for “mapping” 5 cm-diameter beam position monitors (BPMs) used in the Low Energy Demonstrator Accelerator (LEDA) at Los Alamos is described. Two-dimensional data is accumulated from the four micro-stripline electrodes in the probe by sweeping an antenna driven at the LEDA bunching frequency of 350 MHz in discrete steps across the aperture. These data are then used to determine the centroid, Fistand thud-order sensitivities of the BPM. These probe response coefficients are then embedded in the LEDA control system database to provide normalized beam position information to the operators. A short summary of previous systems we have fielded is given, along with their attributes and deficiencies that had a bearing on this latest design. Lessons learned from this system will, in turn, be used on the next mappers that are currently being designed for 15 cm and 2.5 cm BPMs. BACKGROUND We have implemented several BPM characterization systems for previous projects at Los Alamos. The first system we fielded was a basic “taut-wire” fixture whereby a wire antenna was stretched through the BPM between two parallel plates mounted on micrometer-driven X-Y linear stages. The antenna was driven at the accelerating cavity frequency while the signals at the output ports were monitored with a power meter and manually recorded as the stages incrementally translated the antenna across the aperture. Some of the drawbacks to this system were: 1) A high chance for error in the manual positioning of the stages and data recording of the outputs of all four ports for each increment. This slow and * Work funded and supported by the U.S. Department of Energy.