LAUSR

This paper presents a Field Line Tracing code (FLiT) developed to study particle and energy transport as well as other phenomena related to magnetic topology in reversed-field pinch (RFP) and tokamak experiments. The code computes magnetic field lines in toroidal geometry using curvilinear coordinates (r,θ,Φ) and calculates the intersections of those field lines with specified planes. The code also computes magnetic diffusivity and thermal diffusivity due to stochastic magnetic field in the collisionless limit. Compared to Hamiltonian codes no constraints are present on magnetic field functional formulation allowing the integration of whatever magnetic field. The code uses the magnetic field computed solving in toroidal geometry the zeroth-order axisymmetric equilibrium and the Newcomb's equation for the first-order helical perturbation matching the edge magnetic field measurements. Two algorithms have been developed to integrate the field lines: one is a dedicated implementation of a first-order semi-implicit volume-preserving integration method and the other is based on Adams-Moulton, predictor-corrector method. As expected the volume-preserving algorithm is accurate in conserving divergence but slow because the low integration order requires small amplitude steps. Instead the second one proved to be quite fast and able to accurately integrate field lines in many partially and fully stochastic configurations. The code has been already used to study core and edge magnetic topology on the RFX-mod device both in RFP and in tokamak magnetic configuration.