Racetrack FFAGs for medical, PRISM and energy applications

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Fixed-field alternating gradient accelerators (FFAGs) are a hybrid between the traditional cyclotrons used early on in the history of particle accelerators, and the synchrotrons that have come to dominate the world of particle physics: CERN's Large Hadron Collider is the largest example of a proton storage ring, which is a type of synchrotron. Although they were first studied over 50 years ago in small experiments, they were initially considered too computationally complex, and early designs intended to deliver high energy particles were larger than alternative designs. However, recent advances have been made both in the radio frequency cavity technology needed to accelerate heavy particles such as protons, and in the computational tools and magnetic designs of the rings themselves. This renaissance has recently culminated in the demonstration by a Manchester-led collaboration in 2012 of the first non-scaling example of an FFAG, in an experiment called EMMA. Non-scaling FFAGs improve on their forebears by having much smaller magnets, which makes them feasible for high energy accelerators. However, the nature of the acceleration process in these rings can give rise to complex resonant effects that must be managed through careful computational design, and modern designs of the focusing and bending magnets.EMMA demonstrated that the non-scaling principle works, but it has a highly-symmetric layout that makes the accelerator larger than it might be. A so-called Racetrack design dispenses with this symmetry and allows a more compact design whilst increasing flexibility and space for the essential injection and extraction systems: the space is put into the racetrack sections, but is saved elsewhere. Racetrack designs can also solve some of the outstanding problems in delivering a high current of particles at high energies, as required in a number of applications. But no proper racetrack design has yet been produced that examines in detail how all the parts would fit together, and what tolerances would be needed in the magnets to allow it to work. Our proposal intends to do just that.In this project we will look at one useful application of a racetrack FFAG, to providing sufficient energy protons (330 MeV) to allow combined patient radiotherapy treatment and imaging. This combination of treatment and imaging is not currently possible with commercial accelerators, and we think that a racetrack FFAG can made simple enough to compete with other solutions whilst delivering the proton energies required. The lessons learned from designing this example machine will then be used to decide how best to use the racetrack FFAG principle in two other important applications. The first of these is the PRISM experiment, which seeks to measure whether muons can spontaneously transform into electrons, a method which probes the limits of the current Standard Model of Particle Physics. PRISM needs an FFAG to help clean up the muon beam before the decay experiment is performed, and a racetrack FFAG could simplify the design greatly. The second application is to help sustainable nuclear energy. A high-power particle accelerator can be used to help fast nuclear reactors dispose of current and future nuclear waste, including the UK plutonium stockpile, but current technology does not yet provide reliable enough accelerators at low cost. A non-scaling FFAG could do both, but a good method of delivering high currents in a compact accelerator has not yet been demonstrated. Again, a racetrack scheme could be used to enable this. In both these applications we will use the solution obtained in the medical study to outline schemes that could be workable. Thus, this project will try to show how the world-leading work in FFAGs recently carried out in the UK can be applied across a range of useful science and technology.