PERCOLATION SCALING FOR TRANSPORT IN TURBULENT PLASMAS

Guiding centre trajectories in an electrostatic turbulence spectrum ca n be reduced to the motion of charged particles in a two-dimensional r andomly phased potential varying in time, which is known to be describ ed bf a Hamiltonian with 3/2 degrees of freedom and chaotic trajectori es. In order to compute spatial diffusion, a refined model is built he re to describe a broad wavenumber k(-3) spectrum with a very large num ber of waves in a periodic square with a box size larger than the Grus inov coherence length, The root mean square displacement is computed o n a parallel CRAY T3E computer and averaged over time and 1024 initial conditions. Contrary to the traditional Bohm prediction for plasma tu rbulence, it is found that, in the domain of small frequencies or larg e Kuba numbers A similar to E/omega B, the reduced diffusion coefficie nt behaves like A(gamma) with gamma = 0.692 +/- 0.010 in total agreeme nt with the percolation prediction gamma = 7/10. (C) 1998 Published by Elsevier Science B.V.