Results are presented from experimental studies of the formation dynamics, spatial structure, and parameters of a pulse-periodic microwave discharge excited in a coaxial waveguide. The experimental setup allows the stable generation of a plasma jet in molecular and atomic gas flows at pressures close to atmospheric pressure without applying additional initiators. The complicated sequence of processes leading to torch formation cannot be adequately described with conventional models of a discharge sustained by a surface electromagnetic wave.
A microwave coaxial plasmatron (microwave torch) is used as a plasmachemical converter of methane into hydrogen and hydrocarbons. The measured energy cost of methane decomposition is close to its minimum theoretical value. Such a low energy cost is unsurpassed for reactors operating at atmospheric pressure. A model of the plasmachemical converter is constructed. The results of calculations in the frame-work of this model agree well with experimental data.
Experiments indicating acceleration of charged particles as a result of separation of solid surfaces are analyzed. As a possible mechanism of such acceleration, generation of surface charge on the separated surfaces of a cleaved ionic crystal is considered. The maximum electric field generated due to the charging of the separated surfaces and the energy of electrons accelerated in such a field are estimated. It is shown that, for the maximum attainable electric field, conditions are created for the generation of runaway electrons that, even at atmospheric pressure, electrons are accelerated to high energies, not experiencing collisions with gas particles.
The effects of interaction of solar cosmic rays (SCRs) with the heliospheric current sheet (HCS) in the solar wind are analyzed. A self-consistent kinetic model of the HCS is developed in which ions with quasiadiabatic dynamics can present. The HCS is considered an equilibrium embedded current structure in which two main plasma species with different temperatures (the low-energy background plasma of the solar wind and the higher energy SCR component) contribute to the current. The obtained results are verified by comparing with the results of numerical simulations based on solving equations of motion by the particle tracing method in the given HCS magnetic field with allowance for SCR particles. It is shown that the HCS is a relatively thin multiscale current configuration embedded in a thicker plasma layer. In this case, as a rule, the shear (tangential to the sheet current) component of the magnetic field is present in the HCS. Taking into account high-energy SCR particles in the HCS can lead to a change of its configuration and the formation of a multiscale embedded structure. Parametric family of solutions is considered in which the current balance in the HCS is provided at different SCR temperatures and different densities of the high-energy plasma. The SCR densities are determined at which an appreciable (detectable by satellites) HCS thickening can occur. Possible applications of this modeling to explain experimental observations are discussed.
The Earth’s magnetosphere is an open dynamic system permanently interacting with the solar wind, i.e., the plasma flow from the Sun. Some plasma processes in the magnetosphere are of spontaneous explosive character, while others develop rather slowly as compared to the characteristic times of plasma particle motion in it. The large-scale current sheet in the magnetotail can be in an almost equilibrium state both in quiet periods and during geomagnetic perturbations, and its variations can be considered quasistatic. Thus, under some conditions, the magnetotail current sheet can be described as an equilibrium plasma system. Its state depends on various parameters, in particular, on those determining the dynamics of charged particles. Knowing the main governing parameters, one can study the structure and properties of the current sheet equilibrium. This work is devoted to the self-consistent modeling of the equilibrium thin current sheet (TCS) of the Earth’s magnetotail, the thickness of which is comparable with the ion gyroradius. The main objective of this work is to examine how the TCS structure depends on the parameters characterizing the particle dynamics and magnetic field geometry. A numerical hybrid self-consistent TCS model in which the tension of magnetic field lines is counterbalanced by the inertia of ions moving through the sheet is constructed. The ion dynamics is considered in the quasi-adiabatic approximation, while the electron motion, in the conductive fluid approximation. Depending on the values of the adiabaticity parameter κ (which determines the character of plasma particle motion) and the dimensionless normal component of the magnetic field , the following two scenarios are considered: (A) the adiabaticity parameter is proportional to the particle energy and = const and (B) the particle energy is fixed and the adiabaticity parameter is proportional to . The structure of the current sheet and particle dynamics in it are studied as functions of the parameters κ and . It is shown that, in scenario A, the current sheet thickness decreases with increasing adiabaticity parameter due to a decrease in the ion gyroradius. Accordingly, the radius of curvature of magnetic field lines decreases, which leads to an increase in the contribution of electron drift currents near the neutral plane z = 0. Numerical simulations demonstrate that current equilibria can exist if the adiabaticity parameter lies in the range . At κ ~ 0.7, the contribution of electron drift currents to the total current density is much larger than the contribution of ions and the ion motion becomes chaotic. At larger values of the adiabaticity parameter, no equilibrium solutions were found in the framework of the given one-dimensional model. Therefore, the value κ = 0.7 corresponds to the upper applicability limit of the quasi-adiabatic model of the current sheet. In scenario B, an increase in the parameter κ leads to the appearance of a large number of quasi-trapped ions in the current sheet, due to which the current sheet thickens and the amplitude of the current density decreases. As a result, equilibrium solutions exist in a much narrower range of the adiabaticity parameter, . Consequences of the existence of parametric boundaries of equilibrium solutions for the TCS under actual geomagnetic conditions are discussed.
Results are presented from experiments on the inflammation of a stoichiometric methane-oxygen mixture by a high-current multielectrode spark-gap in a closed cylindrical chamber. It is shown that, in both the preflame and well-developed flame stages, the gas medium is characterized by a high degree of ionization (ne ≈ 1012 cm−3) due to chemoionization processes and a high electron-neutral collision frequency (νe0 ≈ 1012 s−1).
The temperature of the neutral component in a repetitive microwave torch excited in an argon jet injected into atmospheric air is measured using different optical methods. The microwave energy is efficiently converted into the thermal energy of the argon jet. The gas temperature is maximum at the nozzle, where it reaches 4.5-5.0 kK, and decreases to 2.5-3.0 kK along the jet. The torch plasma, which is not in thermal equilibrium, drastically influences the working gas and the surrounding air.
A numerical model is developed that allows tracing the time evolution of a current sheet from a relatively thick current configuration with isotropic distributions of the pressure and temperature in an extremely thin current sheet, which plays a key role in geomagnetic processes. Such a configuration is observed in the Earth’s magnetotail in the stage preceding a large-scale geomagnetic disturbance (substorm). Thin current sheets are reservoirs of the free energy released during geomagnetic disturbances. The time evolution of the components of the pressure tensor caused by changes in the structure of the current sheet is investigated. It is shown that the pressure tensor in the current sheet evolves in two stages. In the first stage, a current sheet with a thickness of eight to ten proton Larmor radii forms. This stage is characterized by the plasma drift toward the current sheet and the Earth and can be described in terms of the Chu–Goldberger–Low approximation. In the second stage, an extremely thin current sheet with an anisotropic plasma pressure tensor forms, due to which the system is maintained in an equilibrium state. Estimates of the characteristic time of the system evolution agree with available experimental data.
The existing theory of quasistationary plasma turbulence presumes that the growth rate of plasma waves is zero. In this paper, it is proposed to determine the spectrum of such waves by using the concept of undamped Vlasov waves. The results concerning the ionacoustic velocity in the framework of this concept are presented for two models of ionacoustic turbulence. It is shown that the use of the spectral properties of undamped ionacoustic waves removes the uncertainty in estimating the time and efficiency of strong turbu lent plasma heating.
Linear and nonlinear waves in the near-surface plasma at Phobos and Deimos are considered. It is shown that the motion of the solar wind relative to photoelectrons and charged dust grains violates the isotropy of the electron distribution function in the near-surface plasma at the Martian satellites, which leads to the development of instability and excitation of high-frequency waves with frequencies in the range of Langmuir and electromagnetic waves. Moreover, the propagation of dust acoustic waves, which can be excited, e.g., in the terminator regions of the Martian satellites, is possible. Solutions corresponding to the parameters of the plasma-dust systems over the illuminated parts of the Phobos and Deimos surfaces are found in the form of dust acoustic solitons. The ranges of possible Mach numbers and soliton amplitudes are determined.
The wave processes that take place under the interaction of the Earth’s magnetosphere with dusty plasma near the lunar surface are considered. It is shown that the waves can be excited for the photoelectron parameters corresponding to the quantum yield of the lunar regolith reported by Willis et al. [Photon and Particle Interactions with Surfaces in Space, Ed. by R. J. L. Grard (Reidel, Dordrecht, 1973), p. 389]. Ion-acoustic waves are excited in the regions of the transient magnetic and/or boundary magnetospheric layers due to the onset of linear hydrodynamic instability, whereas dust-acoustic waves are generated due to the onset of linear kinetic instability in the entire region of magnetotail interaction with dusty plasma near the Moon. In both cases, instability is caused by the relative motion of the magnetospheric ions and charged dust grains. The dynamics of the development of ion-acoustic and dust-acoustic turbulence is investigated. Ion-acoustic turbulence is described in terms of strong turbulence theory, while dust-acoustic turbulence is described in terms of weak turbulence theory. The energy density of oscillations, the effective collision frequencies, and the electric fields arising in the system are determined for both ion-acoustic and dust-acoustic turbulences. It is shown that the development of ion-acoustic turbulence in the dusty plasma system near the Moon can lead to the generation of electric fields that are somewhat weaker than those arising near the lunar surface due to the charging of the Moon’s surface under the action of solar radiation, but still sufficiently strong to affect the electric field pattern above the Moon. The obtained effective collision frequencies should be taken into consideration when deriving hydrodynamic equations for dusty plasma ions with allowance for turbulent plasma heating.
Propagation and amplification of extraordinary electromagnetic waves in a dipole magnetic field in a narrow 3D plasma cavity in which a weakly relativistic electron beam propagates along the magnetic field in the direction of the gradient of the magnetic field strength is investigated. The domain of wave vectors at the starting point for which the wave amplification factors at the output of the density cavity reach their maximum values is found, and the amplification factor as a function of the wave frequency is determined. It is shown that the longitudinal velocity of fast electrons, which enables generation of waves in a broader frequency range, plays an important role in the formation of the spectrum of the auroral kilometric radiation (AKR). In this case, waves with the largest amplification factors at the output of the cavity have frequencies exceeding the cutoff frequency of the background plasma at the wave generation altitude. The global inhomogeneity of the magnetic field and plasma density, which governs the residence time of the waves in the amplification region, plays a key role in the formation of the AKR spectrum. It is shown that this time is the main factor determining the energy of the waves emerging from the source.
A self-consistent model of the formation and evolution of dusty plasma structures in the ionospheres of the Earth and Mars is presented. The model allows describing the formation of a stratified dust structure as a result of dust cloud evolution in the Earth's ionosphere. The structure forms due to the splitting of the primary cloud and is characterized by the presence of a cluster of dust grains at altitudes corresponding to noctilucent clouds and polar mesosphere summer echoes. The characteristic formation time of polar mesospheric clouds in the Earth’s ionosphere obtained within this model agrees with observational data. The possibility of the formation of oversaturated carbon dioxide clouds in the Martian ionosphere, similar to noctilucent clouds in the Earth's ionosphere, is shown. It is demonstrated that phenomena similar to polar mesosphere summer echoes on the Earth can also take place in the Martian ionosphere. The theoretically estimated dimensions and charges of dust grains in the Martian ionosphere agree with observational data.
The process of relaxation of energetic O– ions formed via dissociative attachment of electrons to molecules in the discharge plasmas of water vapor and H2O: O2 mixtures in a strong electric field is studied by the Monte Carlo method. The probability of energetic ions being involved in threshold ion–molecular processes is calculated. It is shown that several percent of energetic O– ions formed via electron attachment to H2O molecules in the course of plasma thermalization transform into OH– ions via charge exchange or are destroyed with the formation of free electrons. The probabilities of charge exchange of O– ions and electron detachment from them increase significantly (up to 90%) when O– ions are formed via electron attachment to O2 molecules in water vapor with an oxygen additive. This effect decreases with increasing oxygen fraction in the mixture but remains appreciable even when the fraction of H2O molecules in the H2O: O2 mixture does not exceed several percent.
The problem of propagation of an electromagnetic wave in plane-stratified magnetoactive plasma is analyzed. A matrix algorithm of approximate solution of a set of wave equations is proposed. The algorithm consists in successive finding of the medium-inhomogeneity-induced corrections to the local roots of the dispersion relation and local polarization vectors. The set of field equations is reduced to a set of algebraic equations. The proposed algorithm is convenient for numerical calculations. In contrast to the classical geometrical- optics approximation, the proposed algorithm allows one to take into account the weak effect of linear mode interaction. Examples of numerical calculations of the power reflection coefficient of whistler waves incident on the ionosphere from above are presented. The proposed matrix algorithm can be useful to find the coefficients of reflection and linear transformation of waves in a smoothly inhomogeneous ionosphere.
A steady plasma state reached in the course of charging of an absorbing spherical body is found using computational methods. Numerical simulations provide complete information on this process, thereby allowing one to find the spatiotemporal dependences of the physical quantities and observe the kinetic phenomena accompanying the formation of stable electron and ion distributions in phase space. The distribution function of trapped ions is obtained, and their contribution to the screening of the charged sphere is determined. The sphere charge and the charge of the trapped-ion cloud are determined as functions of the unperturbed plasma parameters.
The interaction of charged dust grains with nonlinear vortical structures in the Earth's atmosphere is analyzed. Certain aspects of the atmosphere-ionosphere interaction, in particular, mechanisms for the appearance of dust grains at ionospheric altitudes, are discussed. It is shown that, at certain altitudes, there are regions in the wavenumber space in which conditions leading to the excitation of acoustic-gravity waves are satisfied. The interaction of nonlinear acoustic-gravity waves with dust grains of meteoric origin at ionospheric altitudes, which leads to the mixing and redistribution of dust grains over the region where vortices exist, is investigated. The possibility of formation of vertical and horizontal dust flows in dusty ionospheric plasma as a result of modulational instability is analyzed. The dynamics of dust grains in dust devils frequently arising in the atmosphere above well-heated surfaces is modeled. The vortical structure of such a dust devil is characterized by a reduced pressure in the center, which facilitates the lifting of small dust grains from the surface. The formulated model is used to calculate the trajectories of dust grains in dust devils with allowance for the influence of the electric field generated in the vortex by colliding dust grains. The calculations show that dust devils play an important role in the transport of dust grains.