Enhancement of the velocity diffusion in longitudinal plasma turbulence

Velocity diffusion has been observed to be significantly above that given by quasilinear theory in both test-particle and self-consistent simulations of the dynamics of turbulent electrostatic fields. Test-particle simulations and analytic calculations for motion in a set of randomly phased waves find the diffusion coefficient to be enhanced by a factor of 2.5 at intermediate values of the overlap parameter. Self-consistent simulations find that the turbulent spectrum can evolve naturally into a form such that the diffusion enhancement is present when the linear growth time of the modes is long compared with the effective discretization time, which is nearly an order of magnitude greater than the resonant broadening time.