Nonlinear Landau damping in collisionless plasma and inviscid fluid

The evolution of an initial perturbation in Vlasov plasma is studied in the intrinsically nonlinear long-time limit dominated by the effects of particle trapping. After the possible transient linear exponential Landau damping, the evolution enters into a universal regime with an algebraically damped electric field, $E\propto 1\mathrm{/}t$. The trick used for the Vlasov equation is also applied to the two-dimensional (2D) Euler equation. It is shown that the stream function perturbation to a stable shear flow decays as $t^{-5\mathrm{/}2}$ in the long-time limit. These results imply a strong non-ergodicity of the fluid element motion, which invalidates Gibbs-ensemble-based statistical theories of Vlasov and 2D fluid turbulence.