Symplectic Computations of Fast Ion Trajectory and Radial Diffusion Coefficient in MHD Perturbed Tokamak

Abstract

The magneto-hydrodynamics (MHD) modes existing in conducting plasmas can greatly affect charged particle’s dynamics. Low frequency MHD perturbations, called the neo-classical tearing (NTM) modes, give rise to magnetic islands which can deteriorate fast ion confinement, especially in tokamak plasmas. Here, a Hamiltonian guiding-center code, based on symplectic algorithm which allows efficient computations of energetic ion trajectories and transport coefficients, has been applied to magnetically perturbed tokamak plasmas. The effects of NTM perturbations on the energetic ion trajectories and diffusion coefficient have been presented. It is demonstrated that the inclusion of such steady state magnetic perturbations in the guiding center drift orbit computations escalates the loss of energetic ions via radial diffusion. Moreover, the broader NTMs lead to a significant enhancement of the radial diffusion coefficient.