Scheme of the evolution of the e-VDF in the (v_⊥, v_||) plane and its interaction with whistler waves as a function of heliocentric distance. Panel a represents the effect of counter-streaming whistler waves at 0.2 AU. Panels b–d show the effect of Strahl-aligned whistler waves between 0.2 and 1 AU. The blue circles represent the core electrons, the green circles the halo electrons, and the red and pink beams the Strahl electrons. The intensity of the color represents the population’s relative density. The resonance velocities (v_res||) for n = ±1 and n = ±2, the drift velocities of the core, halo, and Strahl (noted v_c||, v_H||, v_S||, respectively), and the parallel phase velocities v_φ|| of the waves are indicated along the v_|| axis. The resonance velocities with n = ±3 are not represented for clarity. One of the single-wave characteristics (centered around v_φ||) is represented by an orange dotted line. The path of the diffusing electrons is indicated by the arrows. This diffusion takes place around parallel resonance speeds. The role of the diffusing electrons in the amplification (resp., damping) of the waves is represented by black (resp., grey) arrows.