T Tauri star.

General considerations on the effect of turbulence {#turbulence}
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Observations of interplanetary magnetic turbulence [@Jokipii.Coleman:68 e.g.], and interstellar density measurements [@Armstrong.etal:95] indicate that turbulent fluctuations are typically distributed as a power-law in the turbulent wavenumber (see Fig. \[Pspectrum\]). The small-scale turbulence leads to pitch-angle scattering and cross-field motion of particles, both of which are relevant in general to the propagation of charged particles through a turbulent plasma. As a consequence, the EP trajectories that we calculate significantly differ from radial, as originally assumed by TD09.

![Power-spectrum of the magnetic turbulence used in the test-particle numerical simulations. The vertical lines correspond to the resonant wavenumbers in the magnetic field at a radius $R_s = 5 R_{\star}$ ($B_0 \simeq 0.55$ G) sampled by individual protons with energies $E_k=0.1, 1,10$ GeV in turbulence with $L_c = 10^{-5}$ AU. \[Pspectrum\]](fig1.eps){width="9.cm"}

The amount of scattering of EPs depends on the level of turbulence in the magnetic field and on the possible amplification of plasma waves by EPs streaming along the field; the latter contribution is neglected in this work. In our simulations, the EPs are injected at various distances from the central star into the circumstellar medium and spend most of their 