Nonlinear Alfvén instability analysis for ITER regimes

ITER will introduce new energetic particle (EP) physics regimes that have not been encountered of existing fusion experiments. The main parameter changes are in the EP gyro radius to machine size ratio and in the Alfvén Mach number (ratio of EP velocity to Alfvén speed); also, multiple fast ion sources and EP species will be present. This leads to dense, closely spaced Alfvén gap structures that lead to novel nonlinear coupling dynamics unlike those in current devices. For example, zonal flow generation/relaxation and successive EP profile flattening/avalanching can enhance EP transport and drive intermittency. To model these effects, large multi-mode simulations need to be followed in the saturated state for timescales long enough to capture the relevant dynamics. The nonlinear FAR3d gyro-Landau closure model has been developed for these goals and has been adapted to several ITER cases both in the pre-fusion power and the full fusion power regimes. The hybrid (MPI/OpenMP) parallelism of this model has allowed global nonlinear simulations including up to 20 coupled toroidal mode number families over a range of helicities (m/n) that cover ~90% of the minor radius. Features of EP driven turbulent transport in ITER’s fusion power regime will be described.