Magnetic Design of a Compact GaToroid for Very High Energy Electron and Pre-Clinical Hadron Beams

GaToroid is a novel configuration of a beam delivery system for charged particles therapy based on a steady-state, axis-symmetric field configuration. The basic idea is to use fixed toroidal magnets, producing an axis-symmetric (or periodical axis-symmetric) field configuration that can bend beams from several directions onto the patient location. In principle, neither magnets nor patient need to be moved. In addition, the field of the magnets of this toroidal gantry is static. Such system is perfectly adapted to FLASH therapy, a novel method of beam dose delivery that has shown benefits for electrons and potential for hadrons. In this paper we describe the magnetic design of a “compact GaToroid”, which could be built with iron-dominated magnets, suitable for 200 MeV electron beams, as well as protons at 70 MeV. The gantry profits from the use of toroidal quadrupoles, which greatly simplify the beam transmission. An additional novelty is the use of a resonant kicker as the vector magnet. Starting from the requirements for beam transmission, we derive first the magnet main characteristics (strength, aperture, size and mass) and report the detailed magnetic field calculations in support of the design.