Final test particle energy spectra for various scattering models. In all cases 5 × 10⁵ test particle orbits are calculated, then each orbit is weighted in proportion to the local density at the initial position of the orbit to ensure the initial energy distribution is a Maxwellian at T = 10⁶ K, and that the initial pitch angle cosine distribution is uniform. Section 4.1 shows the initial conditions of the simulations. In panels a and b we set α = 0 and vary the value of κ, whereas in panel c we take κ = η_sp/η_a and vary α. Panel d shows the spectra from panel b between 1 and 100 keV.