LEDA and APT beam position measurement system: Design and initial tests

Beam position measurements are being designed and fabricated for the Low Energy Demonstration Accelerator (LEDA), a 20-MeV, 100-mA-cw proton-accelerator, presently under construction at Los Alamos. Similar position measurements will provide position information for a steering scheme within the Accelerator Production of Tritium (APT) linac magnetic lattice. The steering scheme, which centers the beam in the magnetic lattice, uses two position measurements and two translatable quadrupole magnets every 5.5-FODO-lattice periods. What makes these beam position measurements unique is how they will attain, maintain and verify the required accuracy. The position measurement systems consist of micro-stripline beam position monitors (BPMs) and RF coaxial cables, log-ratio processors, on-line error correction sub-systems, and a control system interface including associated algorithms and computer software. This paper discusses the mapping of the BPM probe response, the algorithm used to calculate low beam-velocity response, and the expected log-ratio processor performance