Design of FFA magnet for the laser-hybrid accelerator for radiobiological applications (LhARA)

LhARA, which stands for “Laser-hybrid Accelerator for Radiobiological Applications”, is a novel and flexible facil- ity dedicated to research in radiobiology. A proton beam of energy up to 15 MeV can be produced by a laser driven source, the beam then enters a Fixed Field Alternating (FFA) gradient accelerator for acceleration to produce a variable ex- traction energy between 15-127 MeV. To avoid uncontrolled beam loss, the operational tune was picked carefully to avoid resonances. The magnetic field must be adjusted to ensure that the tune stays at the same working point for different energy ranges. The FFA ring uses combined-function spiral magnets, which create a radial magnetic gradient through distributed conductors wrapped around the pole, each car- rying a different current. A three-dimensional study was carried out in OPERA 3D and the parameters of the magnet were optimized. The results showed that resonances up to fourth order were avoided for the entire range of acceleration for different operational energies entire range of acceleration and different operational energies.