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An exact solution of the collisionless time-dependent Vlasov equation is found for the first time. By means of this solution the behavior of the Langmuir waves in the nonlinear stage is considered. The analysis is restricted by the consideration of the first nonlinear approximation keeping the second power of the electric strength. It is shown that in general the waves with finite amplitudes are not subject to damping. Only in the linear approximation, when the wave amplitude is very small, are the waves experiencing damping. It is shown that with the definite resonance conditions imposed, the waves become unstable.

An analytic solution of the time-dependent Boltzmann kinetic equation is found for the first time. The plasma-wall transition (PWT) layer is analyzed using time-dependent velocity distribution functions for electrons and ions. The process of wall charging by electrons is described and estimated. For states close to the time-independent (stationary) state, for which the time dependence of the PWT parameters is weak, (i) the potential shapes in the pre-sheath (PS) and the Debye sheath (DS) are analyzed and (ii) the intermediate region, which bridges the PS and DS sublayers, is defined and its characteristic length is determined. The ion kinetics are dominated by charge exchange with cold neutrals and electron-impact ionization collisions of neutrals. The charge-exchange mean free path λcx is assumed to be constant and much larger than the electron Debye length λDe. The detailed time dependence of the PS sublayer's approach of the stationary state is found. It is proved that the stationary state can be realized only if the floating-potential condition is fulfilled.