Normal-conducting scaling fixed field alternating gradient accelerator for proton therapy

In this paper we present a new lattice design for a 30--350 MeV scaling fixed-field alternating gradient accelerator for proton therapy and tomography---NORMA (NOrmal-conducting Racetrack Medical Accelerator). The energy range allows the realization of proton computed tomography and utilizes normal conducting magnets in both a conventional circular ring option and a novel racetrack configuration, both designed using advanced optimization algorithms we have developed in pyzgoubi. Both configurations consist of ten focusing-defocusing-focusing triplet cells and operate in the second stability region of Hills equation. The ring configuration has a circumference of 60 m, a peak magnetic field seen by the beam of $<1.6\text{ }\text{ }\mathrm{T}$, a maximum horizontal orbit excursion of 44 cm and a dynamic aperture of 68 mm mrad---determined using a novel dynamic aperture (DA) calculation technique. The racetrack alternative is realized by adding magnet-free drift space in between cells at two opposing points in the ring, to facilitate injection and extraction. Our racetrack design has a total magnet-free straight lengths of 4.9 m, a circumference of 71 m, a peak magnetic field seen by the beam of $<1.74\text{ }\text{ }\mathrm{T}$, a maximum horizontal orbit excursion of 50 cm and a DA of 58 mm mrad. A transverse magnet misalignment model is also presented for the ring and racetrack configurations where the DA remains above 40 mm mrad for randomly misaligned error distributions with a standard deviation up to $100\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$.