Extraction from the Accumulator With Rectangular Momentum Distributions

Antiprotons for the Collider will be bunched in the Accumulator using a RF system (ARF4) that operates at a frequency that is four times the revolution frequency of the Accumulator. Four bunches can be extracted from the Accumulator in a single transfer. Since the TEVATRON will operate with 36 antiproton bunches, nine extractions from the Accumulator will be needed. During Run 1, the momentum distribution of the Accumulator core was shaped by the core cooling systems and was approximately gaussian. After an antiproton bunch was extracted from the core, the momentum spread of the beam was increased because of RF displacement. The beam would then be recooled which would delay shot setup (or the phase space density of subsequent extractions would be diluted). Since the number of extractions per shot for Run II is increasing by 50% (from 6 to 9), the extra time due to re-cooling (or the alternative of momentum phase space dilution) might not be acceptable. This note will outline a scheme that will shape the momentum distribution into a rectangle and will extract the beam from the edges of the distribution so that RF displacement is minimized.