We propose an orbit-based representation and modeling technique as a solution for ITER IMAS and similar platforms that need to store and process distributions of charged particles in magnetically confined plasmas. As an example, we apply our methods to the construction of a distribution of fusion-born alpha particles in a large tokamak (JET), showing how pitch angle anisotropy arises naturally in toroidal geometry when the birth profile, which is not a function of the alpha’s constants of motion, is sharply peaked near the center. An iterated circular transformation between orbit- and mesh-based representations is performed for verification and as a proof-of-principle for IMAS applications.26th Meeting of ITPA Topical Group on Energetic Particle Physic
