A low-frequency high-voltage RF-barrier bunching system for high-intensity neutron source compressor rings

A Los Alamos design for a 1-MW pulsed neutron source incorporates a ring utilizing an RF-barrier bunching system. This bunching concept allows uniform longitudinal beam distributions with low momentum spread. Bunching cavities are operated at the revolution frequency (1.5 MHz in our case) and each of the 2nd, 3rd, 4th, and 5th revolution frequency harmonics. Their effects combine to maintain a beam free gap in the longitudinal distribution of the accumulated beam. The cavities are driven by low-plate-resistance common-cathode configured tetrode amplifiers incorporating local RF feedback. Additional adaptive feed-forward hardware is included to reduce the beam-induced bunching-gap voltages well below that achievable solely with RF feedback. Details of this system are presented along with a discussion of the various feed-back and feed-forward techniques incorporated