Anomalous Diffusion and Exit Time Distribution of Particle Tracers in Plasma Turbulence Model

We have explored the character of transport in two plasma turbulence models near marginal stability. One is the resistive pressure-gradient-driven turbulence model and the other a ion-temperature-gradient-driven turbulence model. We work under subcritical conditions with added noise. Under these conditions, there is evidence of avalanche-like transport. To determine the character of the transport, we have followed the motion of tracer particles. Both the time evolution of the moments of the distribution function of the tracer particle radial positions, < \vert r (t) - r (0) \vert^n >, and their finite-size Lyapunov number are used to determine the anomalous diffusion exponent. The numerical results show that the transport mechanism is superdiffusive with an exponent ν (n) close to 0.88 ± 0.07. The distribution of the exit times of particles trapped into stochastic jets is also determined. These particles have the lowest separation rate at the low resonant surfaces.