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Acceleration in the linear non-scaling fixed-field alternating-gradient accelerator EMMA

Abstract

In a fixed-field alternating-gradient (FFAG) accelerator, eliminating pulsed magnet operation permits rapid acceleration to synchrotron energies, but with a much higher beam-pulse repetition rate. Conceived in the 1950s, FFAGs are enjoying renewed interest, fuelled by the need to rapidly accelerate unstable muons for future high-energy physics colliders. Until now a ‘scaling’ principle has been applied to avoid beam blow-up and loss. Removing this restriction produces a new breed of FFAG, a non-scaling variant, allowing powerful advances in machine characteristics. We report on the first non-scaling FFAG, in which orbits are compacted to within 10 mm in radius over an electron momentum range of 12–18 MeV/c. In this strictly linear-gradient FFAG, unstable beam regions are crossed, but acceleration via a novel serpentine channel is so rapid that no significant beam disruption is observed. This result has significant implications for future particle accelerators, particularly muon and high-intensity proton accelerators.

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Figure 1: Orbital period in the EMMA ring as a function of momentum, calculated from the measurement of beam arrival time over ten turns at a single BPM relative to a reference 1.3 GHz sinusoidal radiofrequency signal.
Figure 2: Beam position and cell tune for fixed momentum beams.
Figure 3: Beam position and cell tune for an accelerated beam.
Figure 4: Longitudinal phase space trajectories of beams with five different initial phases.
Figure 5: Standard deviation of beam orbit oscillations in the horizontal and vertical planes, calculated at each cell using a twenty-one cell window.

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Acknowledgements

We greatly appreciate the assistance of the Technology Department at STFC Daresbury Laboratory during the design and construction of EMMA. Our work is supported by the BASROC/CONFORM project (the UK Basic Technology Fund) under Engineering and Physical Sciences Research Council (EPSRC) Grant No. EP/E032869/1, the UK Neutrino Factory project under Particle Physics and Astronomy Research Council (PPARC) Contract No. 2054, Science and Technology Facilities Council (STFC), National Sciences and Engineering Research Council of Canada (NSERC) Grant No. SRO 328338-05 and the US Department of Energy under Contract No. DE-AC02-98CH10886 and DE-AC02-07CH11359.

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Correspondence to S. Machida.

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Machida, S., Barlow, R., Berg, J. et al. Acceleration in the linear non-scaling fixed-field alternating-gradient accelerator EMMA. Nature Phys 8, 243–247 (2012). https://doi.org/10.1038/nphys2179

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