Turbulent transport of beam ions

Abstract

The radial redistribution of energetic ions by background turbulence is investigated by means of linear and nonlinear gyrokinetic simulations with the GENE code [T. Dannert and F. Jenko, Phys. Plasmas 12, 072309 (2005)]. The fast particles are described by an asymmetric and anisotropic Maxwellian distribution function, and they are treated as passive tracers. It is found that there can be a significant fast ion diffusivity for particle energies up to about 10 times the thermal energy, with details depending on the properties of the magnetic geometry and of the microinstabilities driving the turbulence. This finding provides a possible explanation of experimental results concerning the efficiency of neutral beam current drive reported recently from ASDEX Upgrade [S. Günter et al., Nucl. Fusion 47, 920 (2007)].