  We investigate the linear and nonlinear evolution of the ion-acoustic
instability in a collisionless plasma via two-dimensional (2D2V) Vlasov-Poisson
numerical simulations. We initialize the system in a stable state and gradually
drive it towards instability with an imposed, weak external electric field,
thus avoiding super-critical initial conditions that are physically
unrealizable. The nonlinear evolution of ion-acoustic turbulence (IAT) is
characterized in detail, including the particles' distribution functions,
particle heating, (two-dimensional) wave spectrum, and the resulting anomalous
resistivity. An important result is that no steady saturated nonlinear state is
ever reached in our simulations: strong ion heating suppresses the instability,
which implies that the anomalous resistivity associated with IAT is transient
and short-lived. Electron-acoustic waves (EAWs) are triggered during the late
nonlinear evolution of the system, caused by strong modifications to the
particle distribution induced by IAT.
