Design and Magnetic Field Analyses of Spiral Sector Magnet in an FFAG Accelerator for Carbon Cancer Therapy

We designed a coil-dominated magnet wound with coated conductors for a spiral sector fixed-field alternating-gradient (FFAG) accelerator for carbon cancer therapy. The magnet consisted of deformed pancake coils with negative bends. Coils were arranged similar to a ladder to generate the required radial profile of magnetic field. The positions and the number of turns of the coils were iteratively adjusted to reduce the magnetic field error. We carried out numerical electromagnetic field analyses of the designed magnet to evaluate the influence of coated-conductor magnetization (screening or shielding current) on its field quality.