Observation of nonlinear coupling between drift and ion-acoustic oscillations in low-frequency plasma turbulence

It is shown experimentally that the characteristics of structural ion-acoustic turbulence in a plasma are governed primarily by the development of density gradient-driven drift oscillations. The cyclicity of appearance and disappearance of drift wave packets and ensembles of ion-acoustic solitons in a steady-state turbulent plasma, as well as the correlation between them, is determined.     

Ion-acoustic solitons in dusty plasma

The dynamics of dust ion-acoustic solitons is analyzed in a wide range of dusty plasma parameters. The cases of both a positive dust grain charge arising due to the photoelectric effect caused by intense electromagnetic radiation and a negative grain charge established in the absence of electromagnetic radiation are considered. The ranges of plasma parameters and Mach numbers in which ??conservative?? (nondissipative) solitons can exist are determined. It is shown that, in dusty plasma with negatively charged dust grains, both compression and rarefaction solitons can propagate, whereas in plasma with positively charged dust grains, only compression solitons can exist. The evolution of soliton-like compression and rarefaction perturbations is studied by numerically solving the hydrodynamic equations for ions and dust grains, as well as the equation for dust grain charging. The main dissipation mechanisms, such as grain charging, ion absorption by dust grains, momentum exchange between ions and dust grains, and ion-neutral collisions are taken into account. It is shown that the amplitudes of soliton-like compression and rarefaction perturbations decrease in the course of their evolution and their velocities (the Mach numbers) decrease monotonically in time. At any instant of time, the shape of an evolving soliton-like perturbation coincides with the shape of a conservative soliton corresponding to the current value of the Mach number. It is shown that, after the interaction between any types of soliton-like perturbations, their velocities and shapes are restored (with a certain phase shift) to those of the corresponding perturbations propagating without interaction; i.e., they are in fact weakly dissipative solitons.     

Ion-acoustic solitons in Bi-Ion dusty plasma

The propagation of ion-acoustic solitons in a warm dusty plasma containing two ion species is investigated theoretically. Using an approach based on the Korteveg de Vries equation, it is shown that the critical value of the negative ion density that separates the domains of existence of compression and rarefaction solitons depends continuously on the dust density. A modified Korteveg de Vries equation for the critical density is derived in the higher order of the expansion in the small parameter. It is found that the nonlinear coefficient of this equation is positive for any values of the dust density and the masses of positive and negative ions. For the case where the negative ion density is close to its critical value, a soliton solution is found that takes into account both the quadratic and cubic nonlinearities. The propagation of a solitary wave of arbitrary amplitude is investigated by the quasi-potential method. It is shown that the range of dust densities around the critical value within which solitary waves with positive and negative potentials can exist simultaneously is relatively wide.     

Nonlinear theory of ion-acoustic waves in an electron-positron-ion plasma

An analytical nonlinear gasdynamic theory of ion-acoustic waves in an e-p-i plasma is developed for the case in which all the plasma components in the wave undergo polytropic compression and rarefaction. An exact solution to the basic equations is found and analyzed by the Bernoulli pseudopotential method. The parameter range in which periodic waves can propagate and the range in which solitary waves (solitons) exist are determined. It is shown that the propagation velocity of a solitary is always higher than the linear ion sound velocity. The profiles of all the physical quantities in both subsonic and supersonic waves are calculated. The results obtained agree well with both the data from other papers and particular limiting cases.     

Helicon plasma source in the ion-acoustic frequency range

A helicon plasma source operating in the ion cyclotron frequency range is studied theoretically. It is shown that, even with a purely inductive antenna exciting a helicon wave in a plasma at ion-acoustic frequencies, the effective resistance characterizing the absorption of high-frequency field energy is determined by the ion-acoustic field generated by the helicon wave. Calculations show that such a plasma source can operate very efficiently.     

Ion-acoustic Gardner solitons in a four-component nonextensive multi-ion plasma

The nonlinear propagation of ion-acoustic (IA) solitary waves (SWs) in a four-component non-extensive multi-ion plasma system containing inertial positively charged light ions, negatively charged heavy ions, as well as noninertial nonextensive electrons and positrons has been theoretically investigated. The reductive perturbation method has been employed to derive the nonlinear equations, namely, Korteweg?deVries (KdV), modified KdV (mKdV), and Gardner equations. The basic features (viz. polarity, amplitude, width, etc.) of Gardner solitons are found to exist beyond the KdV limit and these IA Gardner solitons are qualitatively different from the KdV and mKdV solitons. It is observed that the basic features of IA SWs are modified by various plasma parameters (viz. electron and positron nonextensivity, electron number density to ion number density, and electron temperature to positron temperature, etc.) of the considered plasma system. The results obtained from this theoretical investigation may be useful in understanding the basic features of IA SWs propagating in both space and laboratory plasmas.     

Vlasov modes in the theory of ion-acoustic turbulence

The existing theory of quasi-stationary 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 ion-acoustic velocity in the framework of this concept are presented for two models of ion-acoustic turbulence. It is shown that the use of the spectral properties of undamped ion-acoustic waves removes the uncertainty in estimating the time and efficiency of strong turbulent plasma heating.     

Low-threshold parametric excitation of the upper hybrid wave in experiments on electron-cyclotron resonance heating by an ordinary wave

The possibility of the low-threshold decay of an ordinary wave into an upper hybrid wave localized in a plasma column (or in an axisymmetric plasma filament) and a low-frequency wave is analyzed. It is shown that the threshold for such a decay, accompanied by the excitation of an ion-acoustic wave, can easily be overcome for plasma parameters typical of model experiments on the Granit linear plasma facility.     

Ion-acoustic “Houston's horse” effect

The structure of an ion-acoustic forerunner excited by a shock wave in a weakly ionized plasma is studied. It is shown that, when the shock velocity exceeds the ion-acoustic speed, a soliton bunch is produced at the perturbation front. The increase in the shock velocity to a certain critical value is accompanied by an increase in the soliton amplitude. A further increase in velocity leads to an explosive-like collapse of the bunch, which results in a decrease in the medium resistance. This phenomenon is analogous to the “Houston's horse” effect in narrow-channel hydrodynamics.     

Ion-acoustic soliton in a plasma with finite-temperature ions

The influence of the ion temperature on the properties of ion-acoustic solitons is considered. The critical parameters, the role of reflected ions, and the soliton profile are analyzed. The soliton evolution is studied using numerical simulations. The stability of stationary solutions is demonstrated. The results obtained are compared with the Korteweg-de Vries soliton and available experimental data.     

Solitons and energy transfer along protein molecules

It is shown that the energy released in the hydrolysis of ATP molecules can be transferred in the form of vibration solitons along α-helical protein molecules. The vibration solitons are collective excitations travelling along a chain of successively arranged peptide groups and corresponding to amide I vibrations. The exceptional stability of solitons in one-dimensional structures can account for the small probability of their energy transforming into that of disordered heat motion.     

Supernonlinear Waves in Plasma

A new class of nonlinear waves in plasma??supernonlinear waves (SNWs) characterized by the nontrivial topology of their phase portraits??has been revealed. The topological classification of such waves is given, and suitable notation for them is proposed. It is demonstrated using several examples that SNWs can exist in the form of plasma waves of different physical nature, e.g., electrostatic (ion-acoustic) and MHD (Alfvén) waves. It is shown that a necessary condition for the existence of SNWs is the presence of at least three different charged plasma components (electrons, positrons, ions, dust grains, etc.). As the number of plasma components increases, the topology of the SNW phase portrait becomes more complicated. Typical indications of SNWs are given, which make is possible to easily reveal such waves experimentally.     

Solitary fast magnetosonic waves propagating obliquely to the magnetic field in cold collisionless plasma

Solutions describing solitary fast magnetosonic (FMS) waves (FMS solitons) in cold magnetized plasma are obtained by numerically solving two-fluid hydrodynamic equations. The parameter domain within which steady-state solitary waves can propagate is determined. It is established that the Mach number for rarefaction FMS solitons is always less than unity. The restriction on the propagation velocity leads to the limitation on the amplitudes of the magnetic field components of rarefaction solitons. It is shown that, as the soliton propagates in plasma, the transverse component of its magnetic field rotates and makes a complete turn around the axis along which the soliton propagates.     

Nonlinear dynamics of a nonisothermal collisionless plasma flow

It is shown that the two-fluid electrohydrodynamic equations for a transversely homogeneous flow of cold ions and Boltzmannian electrons in the ion-acoustic region are reduced to the Boussinesq equation. Using a two-soliton solution as an example, the nonlinear mechanism of collisionless relaxation of a supersonic plasma flow toward a steady state in the form of a double space charge layer is demonstrated.     

Relativistic Ion-Acoustic Solitary Waves in a Magnetized Pair Ion Dense Plasma with Nuclei of Heavy Elements

The propagation of ion-acoustic solitary waves (IASWs) in a magnetized collisionless degenerate plasma system for describing collective plasma oscillations in dense quantum plasmas with relativistically degenerate electrons, oppositely charged inertial ions, and positively charged immobile heavy elements is investigated theoretically. The perturbations of the magnetized quantum plasma are studied employing the reductive perturbation technique to derive the Korteweg–de Vries (KdV) and the modified KdV (mKdV) equations that admit solitary wave solutions. Chandrasekhar limits are used to investigate the degeneracy effects of interstellar compact objects through the equation of state for degenerate electrons in nonrelativistic and ultrarelativistic cases. The basic properties of small but finite-amplitude IASWs are modified significantly by the combined effects of the degenerate electron number density, pair ion number density, static heavy element number density, and magnetic field. It is found that the obliqueness affects both the amplitude and width of the solitary waves, whereas the other parameters mainly influence the width of the solitons. The results presented in this paper can be useful for future investigations of astrophysical multi-ion plasmas.     

Action of an electromagnetic pulse on a plasma with a high level of ion-acoustic turbulence. Field diffusion and subdiffusion

Specific features of the interaction of a relatively weak electromagnetic pulse with a nonisothermal current-carrying plasma in which the electron drift velocity is much higher than the ion-acoustic velocity, but lower than the electron thermal velocity, are studied. If the state of the plasma with ion-acoustic turbulence does not change during the pulse action, the field penetrates into the plasma in the ordinary diffusion regime, but the diffusion coefficient in this case is inversely proportional to the anomalous conductivity. If, during the pulse action, the particle temperatures and the current-driving field change due to turbulent heating, the field penetrates into the plasma in the subdiffusion regime. It is shown how the presence of subdiffusion can be detected by measuring the reflected field.     

Nonlinear mechanism for weak photon emission from biosystems

The nonlinear mechanism for the origin of the weak biophoton emission from biological systems is suggested. The mechanism is based on the properties of solitons that provide energy transfer and charge transport in metabolic processes. Such soliton states are formed in alpha-helical proteins. Account of the electron-phonon interaction in macromolecules results in the self-trapping of electrons in a localized soliton-like state, known as Davydov's solitons. The important role of the helical symmetry of macromolecules is elucidated for the formation, stability and dynamical properties of solitons. It is shown that the soliton with the lowest energy has an inner structure with the many-hump envelope. The total probability of the excitation in the helix is characterized by interspine oscillations with the frequency of oscillations, proportional to the soliton velocity. The radiative life-time of a soliton is calculated and shown to exceed the life-time of an excitation on an isolated peptide group by several orders of magnitude.     

Wave processes during the interaction of the Earth’s magnetotail with dusty plasma near the lunar surface

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.     

Collision of Ion-Acoustic Solitary Waves in Plasma

The process of collision of ion-acoustic solitary waves in a collisionless plasma with cold ions and Boltzmann electrons is studied using numerical simulations. It is shown that solitary waves with sufficiently large amplitudes do not preserve their identity after the collision. Their amplitudes decrease, and the shapes change. It is found that the collision is accompanied by the generation of fast ions with velocities exceeding threefold the ion sound speed.     

Nonlinear ion acoustic waves in a quantum degenerate warm plasma with dust grains

A study is made of the propagation of ion acoustic waves in a collisionless unmagnetized dusty plasma containing degenerate ion and electron gases at nonzero temperatures. In linear theory, a dispersion relation for isothermal ion acoustic waves is derived and an exact expression for the linear ion acoustic velocity is obtained. The dependence of the linear ion acoustic velocity on the dust density in a plasma is calculated. An analysis of the dispersion relation reveals parameter ranges in which the problem has soliton solutions. In nonlinear theory, an exact solution to the basic equations is found and examined. The analysis is carried out by Bernoulli’s pseudopotential method. The ranges of the phase velocities of periodic ion acoustic waves and the velocities of solitons are determined. It is shown that these ranges do not overlap and that the soliton velocity cannot be lower than the linear ion acoustic velocity. The profiles of the physical quantities in a periodic wave and in a soliton are evaluated, as well as the dependence of the critical velocity of solitons on the dust density in a plasma.