Probability of non-thermal properties of alpha particles with respect to protons as a function of Coulomb number, N_c, during encounter 10. Panels a and b show the alpha-to-proton temperature ratio, T_α/T_p, and the magnitude of differential speed over local Alfvén speed, |V_αp|/V_A, are ordered by collisionality. The white horizontal line in panel a represents the thermal equilibrium when T_α = T_p. The white dashed vertical lines in panels a and b show N_c = 0.02 and be used in Fig. 2.