Intrinsic trapping of stochastic sheared magnetic field lines

The decorrelation trajectory method is applied to the diffusion of magnetic field lines in a perturbed sheared slab magnetic configuration. Some interesting decorrelation trajectories for several values of the magnetic Kubo number and of the shear parameter are exhibited. The asymmetry of the decorrelation trajectories appears in comparison with those obtained in the purely electrostatic case studied in earlier work. The running and asymptotic diffusion tensor components are calculated and displayed.

Figure 1

Decorrelation trajectories for $K_m=0.1$ Solid line: ${\theta }_s=6$. Dashed line ${\theta }_s=1$. Dotted line ${\theta }_s=0$.

Figure 2

Same as in Fig. 1 but for $K_m=1$.

Figure 3

Same as in Figs. 1, 2 but for $K_m=3$.

Figure 4

The running diffusion coefficients for $K_m=0.1$ and for four values of the shear parameter. In all pictures ${\theta }_s=0$ (dotted line), ${\theta }_s=0.2$ (dash-dotted line), ${\theta }_s=1$ (dashed line), and ${\theta }_s=6$ (solid line).

Figure 5

Same as in Fig. 4 but for $K_m=1$.

Figure 6

Same as in Figs. 4, 5 but for $K_m=3$.

Figure 7

The diagonal asymptotic diffusion coefficient $D_{xx}^{as}$ as a function of the magnetic Kubo number $K_m$ for different values of the shear parameter in a ${\log }_{10}\text{−}{\log }_{10}$ plot. Diamonds: ${\theta }_s=6$. Squares: ${\theta }_s=1$. Circles: ${\theta }_s=0$.

Figure 8

Same as in Fig. 4 but for $D_{yy}^{as}$.