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Neutrino Factory/Muon Collider Document 566-v2

Bunch Coalescing in a Helical Channel

Document #:
Document type:
MuCool Note
Submitted by:
Cary Y Yoshikawa
Updated by:
Cary Y Yoshikawa
Document Created:
25 Jul 2011, 17:12
Contents Revised:
28 Jul 2011, 11:56
Metadata Revised:
28 Jul 2011, 11:56
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29 Jul 2011, 14:32
28 Jul 2011, 12:01
26 Jul 2011, 11:41
A high-luminosity Muon Collider requires bunch recombination for optimal luminosity. In this report, we take advantage of the large slip factor in a helical transport channel (HTC) to coalesce bunches of muons into a single one over a shorter distance than can be achieved over a straight channel. To reduce complications associated with matching out of upstream and into downstream subsystems, we designed the bunch coalescing subsystem with a value for the slip factor that is representative of an existing helical cooling channel (HCC) design. Alternate designs have been developed to investigate the tradeoffs between simplifications in reducing the number of RF cavities versus performance. All key components of the bunch coalescing subsystem have been simulated in 3-D. Excluding the initial acceleration of all bunches to the desired operating energy (not simulated), the coalescing subsystem that is designed to merge 9 bunches has a horizontal length of ~105m and is able to achieve efficiencies of 99.7%, 98.4%, and 94.2% for 9, 11, and 13 bunches, respectively, where each bunch has emittances expected at the end of a HCC. Designs to merge more bunches will be longer, but should achieve comparable efficiencies. The simplified designs incorporating fill factors for RF cavities of ~25% and ~50% obtained efficiencies of 96%, 94-95%, and 90-91% for 9, 11, and 13 bunches, respectively. The efficiencies above do not include decay losses, which would be ~8% for muons with kinetic energy of 200 MeV. Following the RF capture into a single bunch, a series of radial wedges in the helical channel may be needed to reduce the longitudinal emittance (via emittance exchange afforded by allowable growth of transverse emittance) as well as reduce the operating energy to that of the second HCC. The amount of longitudinal cooling and energy reduction for the single bunch is dependent on the acceptance of the downstream HCC, which is yet to be designed. Results of the coalesced single bunch provide a starting point for an iterative process between the bunch coalescer and HCC with aim to create the shortest and most efficient integrated design that accepts a hot string of muon bunches and produces a single cooled bunch that is ready for extreme cooling (emittance exchange), acceleration, and collision with its particle counterpart at the energy frontier.
muon bunch merge coalesce
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