A. P. Golub

Dust ion-acoustic shock-wave structures: Theory and laboratory experiments

An evolutionary theoretical model is developed that describes dust ion-acoustic shock waves in dusty plasma consisting of ions (treated in the hydrodynamic approximation), Boltzmann electrons, and variable-charge dust grains. Account is taken not only of ionization, absorption, momentum loss by electrons and ions in collisions with dust grains, and gas-kinetic pressure effects but also of the processes peculiar to laboratory plasmas. It is shown that the model is capable of describing all the main experimental results on dust ion-acoustic shock waves [Q.-Z. Luo et al., Phys. Plasmas 6, 3455 (1999); Y. Nakamura et al., Phys. Rev. Lett., 83, 1602 (1999)].

Dusty Plasma at the Surface of the Moon

A theoretical model that provides a self-consistent description of the concentrations of photoelectrons and dust particles located over the illuminated part of the lunar surface is presented. The model takes account of the observation point location and the effects of production of photoelectrons at the surfaces of the Moon and dust particles, the dynamics of dust particles in the electric and gravitational fields, and the charging of dust particles through their interaction with the solar radiation photons, the solar wind electrons and ions, photoelectrons, etc. An expression that describes the distribution of photoelectrons over the illuminated part of the lunar surface is obtained. The size and elevation distributions of the charged dust particles located over the illuminated part of the lunar surface are calculated for different angles between the local normal and the direction to the Sun. It is shown that no substantial restrictions are imposed on the choice of the landing site for future lunar spacecraft missions aimed at studying the near-surface dust on the Moon.

Weakly dissipative dust-ion-acoustic solitons in complex plasmas and the effect of electromagnetic radiation

Possibility for dust ion-acoustic solitons to exist in complex (dusty) plasmas in the presence of electromagnetic radiation, which results in positive dust particle charges, is investigated. Dissipative processes occurring during the propagation of dust ion-acoustic perturbations, among which are the charging of dust grains, the absorption of ions by grains, the transfer of the ion momentum to the grains, and ion-neutral collisions, are taken into account. Temporal evolution of the soliton-like perturbation and interaction of two soliton-like perturbations are studied. Compressive soliton-like perturbations are shown to possess the main properties of the soltons, in particular, the interacting perturbations conserve their form.

Dusty plasma system in the surface layer of the illuminated part of the moon

The dusty plasma system in the surface layer of the illuminated part of the Moon has been considered. The maximum height of the dust rise has been determined. It has been shown that a dead zone, where dust particles cannot rise over the surface of the Moon, is absent near a lunar latitude of 80°. The size and height distributions of dust have been determined.

On the distributions of photoelectrons over the illuminated part of the moon

The existing view of the photoemission properties of lunar regolith does not provide the unambiguous treatment of the parameters and distributions of photoelectrons over the illuminated part of the Moon. This is indicated by the present calculations of the density, temperature, and distribution function of photoelectrons. It has been demonstrated that the quantum yield of lunar regolith is the main parameter determining the generation of photoelectrons near the surface of the Moon. At present, this parameter is determined with significant uncertainty. The measurement of the quantum yield of regolith directly on the surface of the Moon has been proposed as a variant of the solution of the indicated problem. Such measurements can be performed in the framework of future lunar missions.

Impacts of fast meteoroids and the separation of dust particles from the surface of the Moon

The possibility of the separation of dust particles owing to impacts of micrometeoroids on the surface of the Moon has been discussed. It has been shown that this effect is significant and should be taken into account when determining the number of particles rising over the surface of the Moon at the formation of a plasma–dust system. The average number of regolith particles leaving the surface of the Moon owing to the impacts of fast meteoroids has been determined for various altitudes over the Moon. The size distribution function of particles leaving the surface of the Moon because of impacts of meteoroids has been determined. It has been shown that impacts of meteoroids constitute an important source of dust microparticles in the plasma–dust system over the surface of the Moon.

Impacts of fast meteoroids and a plasma–dust cloud over the lunar surface

The possibility of the formation of a plasma–dust cloud in the exosphere of the Moon owing to impacts of meteoroids on the lunar surface is discussed. Attention is focused on dust particles at large altitudes of ~10–100 km at which measurements were performed within the NASA LADEE mission. It has been shown that a melted material ejected from the lunar surface owing to the impacts of meteoroids plays an important role in the formation of the plasma–dust cloud. Drops of the melted material acquire velocities in the range between the first and second cosmic velocities for the Moon and can undergo finite motion around it. Rising over the lunar surface, liquid drops are solidified and acquire electric charges, in particular, owing to their interaction with electrons and ions of the solar wind, as well as with solar radiation. It has been shown that the number density of dust particles in the plasma–dust cloud present in the exosphere of the Moon is ≲10−8 cm−3, which is in agreement with the LADEE measurements.

Shock structure formation in dusty plasmas

The problem of the evolution of a perturbation in a dusty plasma and its transformation into a nonlinear wave structure is considered. A computational method that allows one to solve the set of nonlinear evolutionary equations describing variable-charge dust grains, Boltzmann electrons, and inertial ions is developed. Exact steady-state solutions corresponding to ion-acoustic shock structures associated with anomalous dissipation originating from dust grain charging are found taking into account the effect of electron and ion charge separation. The role of this effect increases with the speed of the shock. The evolutions of an initial soliton (which is a steady-state wave solution in a plasma containing dust grains with a constant charge) and an initially immobile perturbation with a constant increased ion density are investigated. In a charge-varying dusty plasma, the soliton evolves into a nonsteady shock wave structure that propagates at a constant speed and whose amplitude decreases with time. The initially immobile perturbation with a constant increased ion density evolves into a shock structure similar to a steady-state shock wave. In the latter case, the compression shock wave is accompanied by a rarefaction region (dilatation wave), which finally leads to the destruction of the shock structure. The solution of the problem of the evolution of a perturbation and its transformation into a shock wave in a charge-varying dusty plasma opens up the possibility of describing real phenomena (such as supernova explosions) and laboratory and active space experiments.

Dusty plasma near the surface of phobos

It has been shown that a dusty plasma is formed in the surface layer over the illuminated part of Mars’ satellite Phobos owing to photoelectric and electrostatic processes. The distribution functions of photoelectrons near its surface, altitude dependences of the density of dust particles, and their charges and sizes, as well as electric fields, have been determined within a physicomathematical model for the self-consistent description of densities of photoelectrons and dust particles over the surface of the illuminated part of Phobos. In view of a weak gravitational field, dust particles rising over the surface of Phobos are larger than those over the surface of the Moon. In this case, the role of adhesion, which is a significant process preventing the separation of dust particles from the lunar surface, is much smaller on Phobos.

Dusty Plasma near the Martian Satellite Deimos

The formation of dusty plasma in the near-surface layer above the illuminated part of the Deimos, the satellite of Mars, due to photoelectric and electrostatic processes is analyzed. Using a physicomathematical model self-consistently describing the densities of photoelectrons and dust grains above the illuminated part of Deimos, the distribution function of photoelectrons near its surface is calculated and the altitude dependences of the electric field, as well as of the number density, charge, and size of dust grains, are determined. It is noted that, due to the lower gravity, substantially larger grains are lifted above the surface of Deimos compared to those lifted above the Moon’s surface. In this case, adhesion, which is believed to significantly hamper the detachment of dust grains from the lunar surface, plays a substantially smaller role on Deimos.