  High-energy particles stream during coronal mass ejections or flares through
the plasma of the solar wind. This causes instabilities, which lead to wave
growth at specific resonant wave numbers, especially within shock regions.
These amplified wave modes influence the turbulent scattering process
significantly. In this paper, results of particle transport and scattering in
turbulent plasmas with excited wave modes are presented. The method used is a
hybrid simulation code, which treats the heliospheric turbulence by an
incompressible magnetohydrodynamic approach separately from a kinetic particle
description. Furthermore, a semi-analytical model using quasilinear theory
(QLT) is compared to the numerical results. This paper aims at a more
fundamental understanding and interpretation of the pitch-angle scattering
coefficients. Our calculations show a good agreement of particle simulations
and the QLT for broad-band turbulent spectra; for higher turbulence levels and
particle beam driven plasmas, the QLT approximation gets worse. Especially the
resonance gap at $\mu=0$ poses a well-known problem for QLT for steep
turbulence spectra, whereas test-particle computations show no problems for the
particles to scatter across this region. The reason is that the sharp resonant
wave--particle interactions in QLT are an oversimplification of the broader
resonances in test-particle calculations, which result from nonlinear effects
not included in the QLT. We emphasise the importance of these results for both
numerical simulations and analytical particle transport approaches, especially
the validity of the QLT.
