An analysis of two experimental observations of Langmuir wave collapse is performed. The corresponding experimental data are shown as evidence against the occurrence of collapses. The physical reason preventing the collapses is found to be the nonresonant electron diffusion in momentum. In this process, plasma thermal electrons are efficiently heated at the expense of wave energy, therefore intense collisionless wave dissipation takes place. The basic reason for the underestimation of nonresonant electron diffusion in the traditional theory is shown to be the substitution of a real plasma by a plasma probabilistic ensemble.

A study of nonresonant electron diffusion refraining from ensemble substitution is performed. It is shown that its intensity is sufficient for suppression of Zakharov's short-wavelength modulational plasma instability [Zakharov, V. E., Sov. Phys. JETP35, 908 (1972)]. This explains the nonoccurrence of Zakharov's Langmuir wave collapse in experiments.

We investigate the structure of nonlinear stationary waves propagating obliquely to the magnetic field in a cold bi-ion plasma. By using the constants of motion that follow from the multi fluid equations, the system may be described by four coupled first-order differential equations. A new constant of motion characterizing a bi-ion flow (called the ‘energy difference integral’) is found. The combination of relations between the flow speeds derived from the conservation laws, which we call the ‘momentum–energy hodographs’, reveal some important features of stationary waves and solitons. Soliton solutions representing both compressions and rarefactions in the ion fluids exist in specific windows in the ‘Alfvén Mach number–obliquity’ space. In other windows, solutions characterized by both oscillating and soliton properties (‘oscillitons’) exist. Critical Mach numbers and propagation angles narrow the size of the windows where smooth soliton solutions can be constructed.

Magnetic reconnection is one of the most efficient ways of transforming magnetic into kinetic and thermal energies. We prove a general identity relating the energy transfer in a neighborhood of a current sheet, where reconnection is assumed to occur. With some reasonable hypotheses regarding the geometry of stream and field lines, we prove that for a constant rate of transformation of magnetic energy, the width of the current sheet must grow with the plasma conductivity. Hence an enhanced diffusivity seems necessary for certain classical models of fast reconnection to work.

The lower-hybrid drift instability of a plasma driven by relative ion–electron motion is analyzed in the framework of the modified magnetohydrodynamic equations. The Hall contribution is expressed in terms that offer a simple physical interpretation of the process and allow a comprehensive study of various features and limits of instability. It is shown that in the chosen terms there are clear-cut ranges of magnetosonic drift, lower-hybrid drift, and kinetic versions of instability that have different properties. It is shown for the first time that the instability may have, besides a flute-like structure, a cell-like one as well. On the basis of the performed analysis, a new classification of the phenomenon is offered.

An intense short-pulse laser propagating through a plasma undergoes self-pulse distortion due to the combined effects of nonlinearity-induced self-focusing and dispersion. The nonlinearity arises as a result of relativistic mass variation. The low-intensity front of the pulse converges mildly, while the high-intensity later portions self-focus strongly. However, at the intensity maxima, the self-focusing effect is masked by the saturation effect of the nonlinear refractive index. The group velocity is also a function of intensity; as a result, the front of the pulse becomes sharpened, while the tail tends to be broadened.