Parallel scattering mean free path as a function of the normalized simulation time vt/ℓ_slab for a slab turbulence with (δB/B₀)² = 0.1. In the upper panel, the case of slab turbulence is shown, while the lower panel shows the case of isotropic turbulence. Both panels show the homogeneous case, i.e., L → ∞. For vt/ℓ_slab ≳ 10², the diffusive regime has been reached where λ_∥ ≈ const. In both panels, the various curves show different particle rigidities R = R_L/ℓ_slab as indicated.