Evolution of electron VDFs and energy profiles of the simulation with n_e/n₀ = 24%. Panels a–c: snapshots of the VDFs at the start (a, t = 0 ), middle (b, 100 ), and end (c, 200 ) of the simulation. Panel d: Temporal variations of energies of the six fluctuated field components. The black line represents the decline of the electron kinetic energy (−ΔE_k). The energies are normalized to the initial kinetic energy of the total electrons. The gray dashed line represents the exponential fitting of the energy profiles. The vertical dotted line in (d) indicates the separate time (120 ) of the linear stage and the saturation stage.