Proposed bunching scheme for a polarized H- injector

Improvements to the polarized H- injector at LAMPF will include a two-stage buncher and beam chopper. The buncher scheme will permit the compression of a major part of the current in 20 RF cycles of the drift-tube linac (100 nsec) into a single RF cycle (5 nsec), thus making possible time-of-flight experiments with the polarized H- beam. A proposed first buncher stage would use a ramp drive waveform; the second stage, a sinusoidal waveform. Design and sensitivity calculations are summarized, including beam energy considerations, buncher and chopper drive requirements, and longitudinal and transverse beam dynamics. The calculations indicate that about 70% of the beam from the source may be bunched in the 1-nsec acceptance region of the linac, with less than 0.1% of the beam in neighboring RF cycles