The Kubo number as a parameter governing the level of chaos in magnetic turbulence

Abstract

It is well known that the Kubo number R allows to classify the transport regimes in turbulent systems. A small Kubo number leads to the so-called quasilinear diffusion coefficient, while a large Kubo number corresponds to the percolative diffusion coefficient. Here we show, by means of a numerical simulation of magnetic field line transport in a three-dimensional anisotropic magnetic turbulence, in which the magnetic fluctuating level and the correlation lengths can be varied independently of each other, that the Kubo number also determines the level of chaos of the magnetic-field lines. We find weak chaos, closed magnetic surfaces, and anomalous transport regimes for R⪡1; widespread chaos, destroyed magnetic surfaces, and quasilinear scaling of the diffusion coefficient for R≳0.3; and global stochasticity as well as the percolation scaling of the diffusion coefficient for R⪢1.