Particle diffusion in anisotropic turbulence

Abstract

We have investigated the diffusion of test particles in anisotropic two-dimensional turbulence. To be specific we have considered electrostatic drift-wave turbulence in magnetized plasma, described by the so-called Hasegawa–Wakatani equations, which produce a two-dimensional turbulent flow-field with a self-consistent instability drive. However, our results are also relevant for particle dispersion in beta-plane turbulence, due to the similarity between drift waves in plasmas and Rossby waves on the beta-plane. In general, we observe that the particle dispersion is strongly anisotropic, with the diffusion in the zonal direction much larger than the diffusion in the direction parallel to the background density gradient––the radial direction (meridional direction for the beta-plane analogy). Trapping of particles in and subsequent displacement with vortical structures leads to an intermediate anomalous diffusion with superdiffusive behaviour in the zonal direction and subdiffusive behaviour in the radial direction. However, the time asymptotic behaviour always approaches a normal diffusive process. By including inertial effects in the particle velocity we observe a tendency for increased superdiffusive behaviour.