Second, to allow for more complex turbulence properties and
to validate the permissibility of the analytical perturbation theories,
one can resort to test particle simulations in specified turbulent
magnetic fields. By tracing particle trajectories, the mean
square displacements and the associated diffusion parameters
can be obtained. On the one hand, there have been successful attempts
to confirm quasi-linear results (Qin & Shalchi 2009). On
the other, such simulations have been employed to investigate
the general behavior of pitch-angle scattering as described by the
direct summation of multiple particle deflections (Lemons et al.
2009). Further examples of application of this method include
the studies of the effects of structured (Laitinen et al. 2012) and
balanced turbulence (Laitinen et al. 2013) on the particle transport,
and consideration of inhomogeneous magnetic background
fields (Tautz et al. 2011; Kelly et al. 2012).