| Paper |
Title |
Page |
| TUPLS070 |
Chromaticity Control in Linear-field Nonscaling FFAGs by Sextapoles
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1657 |
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- S.R. Koscielniak
TRIUMF, Vancouver
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Because of their high repetition rate and large apertures, FFAGs are proposed for high-current medical accelerators suitable for cancer therapy. The linear-field nonscaling FFAG is made from repeating cells containing D and F combined function magnets. The betatron tune profiles decrease with momentum; this leads to the crossing of resonances. We examine how sextapole magnets may be used to flatten the tune profile; in particular (i) whether it is better to place them at the D or F; (ii) what strength is required; and (iii) what is their effect on the closed orbits and path length? The orbit geometry is derived from a thin-element model and the tunes from power series in the quadrupole strength. Chromaticity is corrected by coupling focusing strength to dispersion, which is far stronger in the F element. The zeros of the orbit dispersion become the poles of the "sextapole strength to flatten the tune at some particular momentum". We demonstrate that a weak F sextapole can produce a substantial horizontal tune flattening, and has little impact on other optical properties. Contrarily, placing the sextapole at the D element may destroy the dynamic aperture and or vertical focusing.
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| TUPLS071 |
Minimum Cost Lattices for Nonscaling FFAGs
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1660 |
| |
- S.R. Koscielniak
TRIUMF, Vancouver
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Previously, linear-field FFAG lattices for muon acceleration have been optimized under the condition of minimum path length variation. For non-relativistic particles, as are employed in the hadron therapy of cancer, that constraint is removed allowing a wider range of design choices. We adopt the thin-element kick model for a degenerate F0D0 cell composed of D and F combined function magnets. The dipole field components are parametrised in terms of the bending at the reference momentum and the reverse bend angle. The split between positive and negative bending sets the shape of the closed orbits. The cost function, based on stored magnetic energy, is explored in terms of the split. Two cost minima are found, one corresponding to minimum peak magnet field in the F element, and another to minimum radial aperture in the D element. Analytic formulae are given for the minimization conditions. The minimum field lattice is similar to existing designs based on minimizing the path length variation, but the minimum aperture lattice presents a new direction for future detailed design studies.
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| TUPLS072 |
Nonscaling FFAG with Equal Longitudinal and Transverse Reference Momenta
|
1663 |
| |
- S.R. Koscielniak
TRIUMF, Vancouver
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An unusual feature of linear-field nonscaling FFAG designs is that the radio-frequency is not necessarily synchronous with the reference orbit and momentum chosen for the lattice design. This arises because optics design prefers the reference geometry to be composed of straight lines and arcs of circles - either at the mean momentum, or at high momentum to centre the orbit in the F element. The asynchronous acceleration proposed for rapid acceleration has strong requirements to set the longitudinal reference at 1/4 and 3/4 of the momentum range to minimize phase slip. The usual particle-tracking programs, such as MAD, though sophisticated in the transverse plane, are far cruder in their longitudinal working and do not allow for a longitudinal reference momentum and RF phase independent of the transverse values. In the context of a thin-element lattice model, we show how to make the transverse reference momentum and optic design coincident with the longitudinal reference by adjusting the ratio of positive and negative bending in the D and F elements, respectively, and retaining a lines and arcs composition for the reference orbit. This prepares the way for MAD tracking.
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| TUPLS073 |
Formulae for Linear-field Non-scaling FFAG Accelerator Orbits
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1666 |
| |
- M.K. Craddock
UBC & TRIUMF, Vancouver, British Columbia
- S.R. Koscielniak
TRIUMF, Vancouver
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Non-scaling FFAG accelerators using constant-gradient F and D magnets with their fields decreasing outwards can compact ion orbits for a wide range of momentum (e.g., 1:2) into a narrow radial range. Designs to accelerate protons, ions and muons are currently being studied for proton drivers, cancer therapy facilities and neutrino factories. In this paper, analytic formulae are reported for some basic orbit properties, helping to make clear their dependence on the various design parameters and momentum. For the designs tested so far the numerical results are in excellent agreement with those obtained using lattice codes.
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| WEPCH155 |
Tune-stabilized Linear-field FFAG for Carbon Therapy
|
2290 |
| |
- C. Johnstone
Fermilab, Batavia, Illinois
- S.R. Koscielniak
TRIUMF, Vancouver
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The simplicity, smaller aperture, and reduced ring size associated with linear-field, nonscaling FFAGs have made them attractive to investigate for a broad range of applications. Significant progress has recently been made towards understanding and modeling this new type of accelerator. The merits, drawbacks and challenges of the linear-field FFAG are discussed here, in particular its suitability for proton and carbon cancer therapy as compared with conventional synchrotrons and cyclotrons. Specifically, tune stabilization and dynamic aperture, a problem with both scaling and non-scaling FFAGs, will be addressed in detail.
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