On the Mechanisms of Formation of Density Cavities under Instability of Intense Langmuir Oscillations in a Plasma

Abstract

The paper considers the instability of intense Langmuir oscillations in nonisothermal (Zakharov's model) and cold (Silin's model) 1D plasma. The main attention is paid to the formation of plasma density caverns in the hydrodynamic and hybrid (electrons are described hydrodynamically, ions are described by model particles) representations. In the hydrodynamic representation, with a small number of spectrum modes, large-scale plasma density caverns are observed, which rapidly deepen. This process is supported by the appearance of small-scale perturbations, and phase synchronization of the Langmuir waves of the instability spectrum is observed. This phase synchronization of the spectrum modes is quite capable of fulfilling the role that was previously proposed to be given exclusively to the effect of extrusion of particles from the cavity by the field. In hybrid models, in the region of consideration, ions are described by model particles, the number of which in the one-dimensional case 104-5*105 (which in the three-dimensional case corresponds to the number of particles 1012-1014). The initial spectrum of perturbations is very wide and rather intense, which leads to an explosive growth of perturbations in the Zakharov model and a rapid development of instability in the Silin model. In this case, in the developed instability regime, the formation of many small-scale plasma density caverns is observed. It is the presence of this small-scale modulation due to the Fermi effect that quickly forms the normal distribution of ions over velocities. In this case, the effect of particle heating due to Landau damping loses its primacy. It is shown that the caverns practically do not change their position; phase changes for the spectral components of the plasma density were not observed. Only individual small-scale caverns demonstrate dynamics similar to the development of caverns in the hydrodynamic representation.