Transport properties of energetic particles in a turbulent electrostatic field

The diffusion of test particles in a turbulent electrostatic field is investigated numerically. The field is obtained by solving the Hasegawa-Mima model for two-dimensional drift turbulence. It is shown that nonlinear coupling significantly reduces the level of transport compared to the linear regime, and the physical mechanisms leading to this effect are analyzed in detail. Finite Larmor radius effects. relevant to alpha-particle transport in tokamaks, also reduce the diffusion rate. The scaling of the diffusion coefficient with Larmor radius is derived from a closure theory, and the predictions are compared to results from computer experiments. It is suggested that measured diffusion rates of particles with different Larmor radii can be used to obtain information about the turbulence.