Energy density of longitudinal electrostatic waves of 2D simulations in the wave vector space during the saturation time intervals (top row) and at the simulation ends (bottom row). All analyzed intervals are ω_pt_a = 1000 long. The comparison between rows shows that the longitudinal electrostatic waves close to |k| = 0 decrease in time. (a) S1–2D : ω_pt = 2000 − 3000. (b) S2–2D : ω_pt = 1000 − 2000. (c) S3–2D : ω_pt = 3000 − 4000. (d) S1–2D : ω_pt = 9000 − 10 000. (e) S2–2D : ω_pt = 9000 − 10 000. (f) S3–2D : ω_pt = 9000 − 10 000.