Trapped particles in the Reversed Field Pinch

The presence and role of trapped particles in the Reversed Field Pinch (RFP) configuration is considered, with an estimate of their relative population and a description of the characteristic trajectories, in particular for the RFX-mod [1] geometry. The particle's orbit scale lengths (e.g. banana width, mean free path) are classified both for ions and electrons, also in the presence of a background chaotic magnetic field and/or a strong helical modulation of the toroidal equilibrium. The study combines analytical estimates and numerical results obtained with the Hamiltonian guiding center code ORBIT [2] and the equilibrium code FLOW [3]. The impact on particle transport, the origin and the magnitude of the bootstrap current and the amount of the neoclassical correction to the resistivity are investigated, both in axisymmetric and helical geometry.