Analysis of a quasilinear model for ion cyclotron interactions in tokamaks

An orbit averaged quasilinear operator for resonant ion cyclotron interactions is analysed. The regions in phase space where the interactions are strong and the boundaries between regions with resonant and non-resonant ion orbits are identified. At these boundaries the quasilinear diffusion coefficient becomes discontinuous, causing the standard Monte Carlo scheme to induce an unphysical flow of test particles into the region with lower diffusion coefficient. A new Monte Carlo scheme that balances the flows across discontinuities is proposed. Moreover, the quasilinear diffusion coefficient is shown to deviate significantly from the lowest order Larmor radius scaling vertical bar delta H vertical bar(2) proportional to v(perpendicular to)(2n), where delta H is the perturbed Hamiltonian. This is not only caused by the finite Larmor radius effects, but also by the inhomogeneous electric field polarization and by the changes to the guiding centre orbits during the wave-particle interactions.