Arthur Vandenhoeke

Design of a non-scaling FFAG gantry for protontherapy

Abstract

The aim of this internship at IBA (Ion Beam Applications) is the development of a new type of gantry for protontherapy which is able to stand against the new superconductive devices designed by other companies. The main goal is to reduce the size and the weight of the gantry used nowadays to fight cancer, while keeping the strength of the magnets to a reasonable value. This is achieved by replacing energy dependant magnetic fields by fixed-field combined function magnets. These magnets have to be arranged in a focusing-defocussing-focusing sequence called basic cell in order to control the proton beam. This type of sequence allows to propagate a proton beam with a large momentum range without changing the field levels and to reduce by one order of magnitude the offset along the transverse dimension. The first part of the project was to describe such a cell in terms of dispersion, offsets and betatron functions along the transverse dimensions. Empirical adjustments were added at this stage to ensure an optimal geometry for the gantry. In order to ensure the stability of the beam inside the beamline, an additional matching cell was used to fit the periodic solutions of the beam at the border of both parts of the gantry. The program used in the European center for nuclear research called Mad-X allowed to compute the properties of each kind of cell forming the gantry and to finally track the beam along the whole device.