Turbulent Shear Acceleration

We consider particle acceleration by large-scale incompressible turbulence with a lengthscale larger than the particle mean free path. We derive an ensemble-averaged transport equation of energetic charged particles from an extended transport equation which contains the shear acceleration. The ensemble-averaged transport equation describes particle acceleration by incompressible turbulence (turbulent shear acceleration). We find that for Kolmogorov turbulence, the turbulent shear acceleration becomes important in small scale. Moreover, by Monte Carlo simulations, we confirm that the ensemble-averaged transport equation describes the turbulent shear acceleration.