Percolation scaling for transport in turbulent plasmas

Guiding centre trajectories in an electrostatic turbulence spectrum can be reduced to the motion of charged particles in a two-dimensional randomly phased potential varying in time, which is known to be described bf a Hamiltonian with 3/2 degrees of freedom and chaotic trajectories. In order to compute spatial diffusion, a refined model is built here to describe a broad wavenumber k(-3) spectrum with a very large number of waves in a periodic square with a box size larger than the Grusinov coherence length, The root mean square displacement is computed on a parallel CRAY T3E computer and averaged over time and 1024 initial conditions. Contrary to the traditional Bohm prediction for plasma turbulence, it is found that, in the domain of small frequencies or large Kuba numbers A similar to E/omega B, the reduced diffusion coefficient behaves like A(gamma) with gamma = 0.692 +/- 0.010 in total agreement with the percolation prediction gamma = 7/10. (C) 1998 Published by Elsevier Science B.V.