XGC-S study on neoclassical radial energy transport around magnetic islands in toroidal plasmas

In magnetically confined fusion plasmas, the breaking of 'magnetic flux-surfaces' due to resonant magnetic perturbations. can generate magnetic islands and alter field topology to significantly impact plasma confinement and transport dynamics. This work investigates the effect of magnetic islands on neoclassical radial energy transport with in the core plasma using the XGC-S global gyrokinetic particle-in-cell code. By employing kinetic models and a triangular mesh we can capture energy flux structures affected by magnetic islands. We have examined electron and ion dynamics separately to facilitate comparison with neoclassical theory in tokamaks without electric fields. Findings from our simulations revealed enhancements in electron radial energy diffusivity in and around the islands of roughly fifty to one-hundred-fold. The ion response was insignificant in comparison. We observed multiple diffusivity peaks in radial profiles, indicating significant radial energy flux and plasma dynamics along the magnetic field lines. The study also reveals a weaker dependence of enhanced diffusivity on collisionality within the islands compared to predictions from neoclassical theory. Symmetric 2D pressure perturbation profiles suggest pressure flattening, and up-down asymmetric profiles of radial energy flux indicate collisionless plasma dynamics within the magnetic island structure.