Simulation results for the parallel scattering mean free path in isotropic turbulence with adiabatic focusing. The focusing length is chosen as L/ℓ₀ = 10 (upper panel) and L/ℓ₀ = 1 (lower panel). The black diamonds show the case of an absolutely constant turbulence strength as (δB/B₀)² = 0.1 (cf. Fig. 3), whereas the black squares show the case of turbulence strength that varies with the background field strength as (δB/|B|)² = 0.1 (cf. Fig. 4). For comparison, the parallel mean free path is shown also for a homogeneous background magnetic field (gray circles).