Electrostatic oscillations in plasmas with cutoff distributions

When numerically solving the linear Vlasov equation with cutoff electron distributions, the well-known Landau-damped oscillation of the electric field was observed first but, after a short transition time, a constant-amplitude harmonic oscillation with a frequency distinctly higher than Landau's frequency was found. This coexistence of two distinct modes of oscillation - one damped and one undamped - has not been observed before. The behavior is explained quantitatively by comparison of the dispersion equation solution with the results obtained from the numerical solution of Vlasov's equation.