Abstract
Operation with natural chromaticity in a linear nonscaling fixed field alternating gradient (FFAG) accelerator causes crossing of the low order resonances such as integer and half-integer. Although those resonances are not systematic ones, small errors, such as a typical misalignment of $10\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ rms, significantly increase particle amplitude when the accelerator is operated with a slow acceleration rate. For example, there is practically no dynamic aperture if it takes 1000 turns to finish the whole acceleration cycle. Chromaticity correction with sextupole and octupole reduces the maximum available dynamic aperture in a lattice without errors. On the other hand, the accelerator becomes less sensitive to errors. To use a nonscaling FFAG for applications where, unlike a muon accelerator, the large acceptance is not a high priority demand (such as a proton driver or a particle therapy accelerator), chromaticity correction seems to be an essential ingredient.
Highlights
The proposed neutrino factory requires muon acceleration to 20 or 50 GeV=c [1]
From a rf power efficiency point of view, a repetitive use of linac with arcs at both ends was suggested; that is known as a recirculating linear accelerator [2]
Because of the small orbit shift during acceleration which can fit in a single magnet aperture, a beam can circulate for many turns in a fixed field alternating gradient (FFAG) lattice; the rf power requirement is reduced
Summary
The proposed neutrino factory requires muon acceleration to 20 or 50 GeV=c [1]. Since a muon beam has short lifetime of 2:2 s at rest and large emittance of 30 Â 10À3 m rad [1], a suitable accelerator has to accelerate muons quickly with large acceptance. When a FFAG accelerator is used for muon acceleration, the constant tune condition may be violated because a beam circulates for only 10 to 20 turns and the amplitude built up with resonance crossing will be harmless. This paper, intended to study the effects of crossing of the lowest order non systematic resonance because alignment errors were inevitable in practice and space charge effects could be reduced with a high machine repetition rate and a lesser number of particles per bunch. We studied amplitude growth of a particle with tracking simulations in a nonscaling FFAG when it was operated with a much slower acceleration rate than that for muons; we considered proton acceleration with moderate rf voltage. We studied the effects of nonlinearities which reduce the tune excursion
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