Abstract
The new antiproton collector machine (ACOL)[1] presently under development at CERN, requires the highest possible proton intensity (more than 1013 protons per pulse) in one quarter of the PS circumference, and a guaranteed bunching factor, for its p production beam: possibly less than 25ns bunches, 105 ns apart. The present 26 GeV longitudinal technique [2], cannot meet these specifications, so that new quasi-adiabatic processes had to be imagined [3]. First, before transition energy, a bunch pair merging operation reduces from 10 to 5 the number of bunches, with a moderate blow-up, by slowly bunching the beam on half the initial harmonic number. Then, on the high energy flat top, the length of circumference occupied by the bunches is halved, by a technique tentatively named bunch batch compression. This is basically a slow increase of the RF harmonic number seen by the beam, implemented by operating part of the existing cavities stepwise at increasing harmonic numbers (10, 12, 14, 16, 18 and finally 20). Computer outputs are presented, together with machine experiment results.
Highlights
Presently under development at CERN, requires the hiqhest possible proton intensity in one quarter of the PS circumference, and a guaranteed bunching factor, for its p production beam: possibly less than 25ns bunches, 105 ns apart
On the high energy flat top, the length of circumference occupied by the bunches is halved, by a technique tentatively named ‘bunch batch compression”. This is basically a slow increase of the RF harmonic number seen by the beam, implemented by operating part of the existing cavities stepwise at increasing harmonic numbers
Various techniques have been invented for that purpose, and the “26 GeV longitudinal merging” [2] is applied in routine operation
Summary
The ACOL project demands more than 2.10” protons per bunch on the target, at 26 GeV Since this figure is the present record intensity of the CPS injector (PSB), one must merge bunches during the cycle. According to Bozsik et al/s computations, the emittance blow-up is lower than 10 5, when the merging time is greater than 5 synchrotron periods (which, in their case, is the same in the initial and final states). They show that the result is almost independent of space charge repulsion. Bozsik et al c51, and is related to some beam manipulations performed at Fermilab [6]
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