Power transfer and current generation of fast ions with large-ko waves in Tokamak plasmas

The direction and magnitude of power and momentum exchange between fast ions and electrostatic waves in slab and toroidal systems are obtained from global Monte Carlo simulations that include the quasilinear wave‐induced ion diffusion both in velocity space and through a radially localized (lower hybrid) wave structure with propagation in one preferential poloidal direction in tokamaks.
The model considers a full linearized collision model, finite fast ion orbits, and losses in toroidal geometry, and can properly treat the boundary effects on the particle–wave interaction in the configuration space. For an isotropic steady ion source, reduction of wave Landau damping but no wave amplification by wave localization is found for a Gaussian wave intensity distribution in radius, irrespective of the steepness of the radial gradient of the fast ion source rate. Enhanced wave‐driven fast ion current, with magnitude, direction, and profile determined by the boundary conditions, net power transfer, and fast ion radial transport, is found to follow from the asymmetry in the parallel wave number spectrum created by the finite poloidal magnetic field.
In the presence of intense well‐penetrated waves the current carried by fusion α particles can be controlled by the choice of the poloidal wave number spectrum and the total current can greatly exceed the neoclassical bootstrap current of the α particles in a reactor.