Anomalous diffusion and Levy random walk of magnetic field lines in three dimensional turbulence
- Dipartimento di Fisica, Universita della Calabria, I-87030 Arcavacata di Rende (Italy)
The transport of magnetic field lines is studied numerically where three dimensional (3-D) magnetic fluctuations, with a power law spectrum, and periodic over the simulation box are superimposed on an average uniform magnetic field. The weak and the strong turbulence regime, {delta}{ital B}{similar_to}{ital B}{sub 0}, are investigated. In the weak turbulence case, magnetic flux tubes are separated from each other by percolating layers in which field lines undergo a chaotic motion. In this regime the field lines may exhibit Levy, rather than Gaussian, random walk, changing from Levy flights to trapped motion. The anomalous diffusion laws {l_angle}{Delta}{ital x}{sup 2}{sub {ital i}}{r_angle}{proportional_to}{ital s}{sup {alpha}} with {alpha}{gt}1 and {alpha}{lt}1, are obtained for a number of cases, and the non-Gaussian character of the field line random walk is pointed out by computing the kurtosis. Increasing the fluctuation level, and, therefore stochasticity, normal diffusion ({alpha}{congruent}1) is recovered and the kurtoses reach their Gaussian value. However, the numerical results show that neither the quasi-linear theory nor the two dimensional percolation theory can be safely extrapolated to the considered 3-D strong turbulence regime. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
- OSTI ID:
- 172061
- Journal Information:
- Physics of Plasmas, Vol. 2, Issue 7; Other Information: PBD: Jul 1995
- Country of Publication:
- United States
- Language:
- English
Similar Records
Fluid limit of the continuous-time random walk with general Levy jump distribution functions
MODEL OF THE FIELD LINE RANDOM WALK EVOLUTION AND APPROACH TO ASYMPTOTIC DIFFUSION IN MAGNETIC TURBULENCE