Proton distribution functions (υ_x, υ_⊥) – where υ_⊥ is the velocity component perpendicular to the x axis – for cone angles α = 0^° and 90^°. (a) Inside the cavity for α = 90^°, (b) in the upstream reference volume for α = 90^°, (c) inside the cavity for α = 0^°, (d) in the upstream reference volume for α = 0^°. The distribution function is normalised so that the proton density is given by n_p = ∫∫ dυ_xdυ_⊥. The distributions shown are the averages of two different time steps, namely t = 76.8 s and 80 s.