Anomalous diffusion and exit time distribution of particle tracers in plasma turbulence model

To explore the character of transport in a plasma turbulence model with avalanche transport, the motion of tracer particles has been followed. Both the time evolution of the moments of the distribution function of the tracer particle radial positions, [parallel tor(t)-r(0)parallel to (n)], and their finite scale Lyapunov number are used to determine the anomalous diffusion exponent, nu. The numerical results show that the transport mechanism is superdiffusive with an exponent nu 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. (C) 2001 American Institute of Physics.