English: A simplified explanation of nonlinear Landau damping, illustrated as a phase space distribution of electrons accelerated by an electrostatic wave. Initially the electrons are in a uniform Maxwell-Boltzmann distribution with a thermal velocity of 1.6. At time t=1.0s, an externally imposed electrostatic wave turns on, accelerating the electrons. Near the wave's phase velocity (ω/k), more electrons gain energy than lose energy. Thus, the plasma is heated and the wave is damped.

The central plot shows the 2D histogram of electrons in position and velocity. Darker colors mean more electrons and lighter colors mean fewer. The x-axis translates at the wave's phase velocity such that the wave appears stationary. The black lines show the phase space trajectories in the wave's frame of reference. The thick line is the separatrix that divides trapped electrons from untrapped ones.

The upper plot shows the electric field (solid purple) and electric potential (dotted orange) associated with the wave, on the same x-axis as the phase space plot. The signs are inverted such that electrons are repulsed by high potentials and gravitate toward low potentials (even though their charge is technically negative).

The right plot shows the 1D histogram of electrons in velocity space, using the same y-axis as the phase space plot. The dashed black line shows the initial Maxwell-Boltzmann distribution. Note the perturbation to the velocity disribution around the phase velocity late in time.

This plot was generated by code available at github.com/jkunimune/landau-damping