Non-Linear Field Generated by a Distribution of Conductors in a Spiral FFAG

FAGs accelerators re-appeared fifteen years ago to be of interest for new accelerator projects. These synchrotrons allow fast acceleration because of the fixed field magnets. To compensate the beam trajectory radius increase, the radial magnetic gradient follows a non-linear law B₀ (r/R₀)^k. In the frame of the RACCAM (Recherche en Accelerateur et Application Medicales) project in France, a scaling spiral FFAG ring is developed for medical applications. Magnets have spiral edges to make beam focusing. Here is described the dipole design study with flat horizontal poles which allow a low variation of the vertical tune. This study presents how to produce B₀ (r/R₀)^k with distributed polar conductors.