Low frequency collective modes in dense relativistic-degenerate strongly coupled plasma

It is shown that low frequency electrostatic ion mode couples with electromagnetic shear Alfven mode in a dense plasma containing strongly coupled non-degenerate ion and relativistic degenerate electron fluids. By employing the appropriate fluid equations, a linear dispersion equation is obtained which shows modifications due to ion correlations and electron relativistic degeneracy. The results are discussed in the ultra-relativistic and weak-relativistic limits and implications of the results in dense degenerate plasmas of astrophysical origin (e.g., white dwarf stars) are pointed out with possible consequences.     

Ion-temperature-gradient driven modes in dust-contaminated plasma with nonthermal electron distribution and dust charge fluctuations

The effect of nonthermal electrons on ion-temperature-gradient (ITG) driven modes is investigated in the presence of variable dust charge and ion shear flow. The dust charge fluctuating expression is obtained in the presence of kappa distributed electrons. A dispersion relation is derived and analyzed numerically by choosing space plasma parameters of Jupiter/Saturn magnetospheres. It is found that the presence of nonthermal electrons population reduces the growth rate of ITG mode driven instability. The effects of ion temperature, electron density and magnetic field variation on the growth rate of ITG instability are presented numerically. It is also pointed out that the present results will be useful to understand the ITG driven modes with variable dust charge and kappa distributed electrons, present in most of the space plasma environments.     

Korteweg-de Vries equation for ion acoustic soliton with negative ions in the presence of nonextensive electrons

Korteweg-de Vries (KdV) equation for electrostatic ion acoustic wave in a three component plasma containing positive and negative ions along with the nonextensive electrons is derived. Fast and slow ion acoustic modes which propagate with different velocities are excited. The effects of variation of quantities like q (nonextensive parameter), Q (mass ratio of positive to negative ion), μ (electron to positive ion number density ratio), θ _i (positive ion to electron temperature ratio) and θ _n (negative ion to electron temperature ratio) have been presented for fast and slow ion acoustic modes. Both compressive and rarefactive solitons are observed. It is found that the solitary excitations strongly depend on the mass and density ratios of the positive and negative ions as well as on nonextensive electron parameter.     

Propagation of Extremely Low Frequency Waves Through the Ionosphere

The propagation features of extremely low frequency electromagnetic waves through the multicomponent ionospheric plasma are studied. It is shown that at relatively lower frequencies refractive index for right hand mode is higher than the left-hand mode, which is reversed at higher frequencies. The thermal temperature of plasma particle causes decrease in phase and group velocities of both right and left-hand modes. The crossover frequencies for different plasma models are computed and variation with ion concentration and thermal velocity is studied. Explicit expression for group velocity and travel time has been derived and studied numerically. Finally, we have presented simulation of the ion whistler spectrograms for Hydrogen, Helium and Oxygen ions present in the ionospheric plasma. The results are compared with the experimentally detected hydrogen and helium ion whistlers. The importance of the present study in the exploration of ionospheric plasma is illustrated.     

Self-similar expansion of white dwarfs

Properties of plasma expansion that propagates in an electron-positron-ion dense plasma are investigated. Suitable hydrodynamic equations for the ions and ultrarelativistic degenerate electrons and positrons are used. Using self-similar transformation, the basic set of nonlinear equations is solved numerically. Typical values of white dwarf stars are used to estimate the behavior of the ion number density and ion fluid velocity. The positive ions are found to initially slowly escape with high velocity when the ion-to-electron density ratio increases. For higher values of the electron number density, the self-similar solution validity domain decreases. The relevance of the results to white dwarf expansion and collapse is highlight.     

Effects of photoelectron heating and interhemisphere transport on day-time plasma temperatures at low latitudes

The thermal balance of the plasma in the day-time equatorial F region is examined. Steady-state solutions of electron and ion temperatures are obtained, assuming the ions are O⁺ and H⁺. The theoretical concentrations of O⁺ and H⁺ and the field-aligned velocity were obtained following Moffett and Hanson (1973), while theoretical photoelectron heating rates of the electron gas were taken from Swartz et al. (1975).The results demonstrate the gross features in the electron and ion temperatures as observed at the Jicamarca Observatory and in the ion temperatures observed on the OGO-6 satellite. The rapid increase in electron temperature above 500 km at the magnetic equator is due to heating by photoelectrons created at higher latitudes and travelling up along the field lines. The rapid increase in ion temperature is due to good thermal contact with the electrons rather than the neutrals. It is shown that field-aligned interhemispheric thermal plasma flows appreciably affect these temperatures, and that, with a net plasma flow from the summer hemisphere to the winter hemisphere, the temperatures are higher in the winter hemisphere. These effects are related to the character of the ion temperature minimum observed by OGO-6 near the magnetic equator.     

Arbitrary amplitude dust-acoustic double-layers in a warm dusty plasma with suprathermal electrons, two-temperature thermal ions, and drifting dust grains

Arbitrary amplitude dust-acoustic double-layers (DA-DLs) in a plasma with suprathermal electrons, two-temperature thermal ions, and warm drifting dust grains are investigated. Our results reveal that the spatial patterns of the DA-DLs are affected by the degree of the electron suprathermality. The electron thermalization involves a decrease of the cold ion component density, for the existence of localized DA-DLs. An increase of the dust drift velocity requires a decrease of κ (the electron spectral index), for the onset of dust-acoustic double-layers. An increase of the Mach number M leads to an increase of the DL amplitude as well as the corresponding electron spectral index for which the DL occurs.     

A non-linear study of the possible effects of electron-ion collisions on the diffusion of a cylindrical column of ionisation in the Earth's ionosphere

The possible effects of electron—ion collisions on the diffusion of a cylindrical plasma irregularity orientated at right angles to the geomagnetic field lines, at altitude 300 km, are discussed. The results obtained indicate that the diffusion may proceed at a rate rather greater than for a case for which the effects of collisions of electrons with ions are assumed to be negligible. Furthermore, it is suggested that if the plasma density is great enough, the production of a 'fin' of ionisation along the magnetic field direction may be inhibited by the action of electron—ion collisions.     

SIMULATION STUDIES OF ACCELERATION OF HEAVY IONS AND THEIR ELEMENTAL COMPOSITIONS

By using a one-dimension (one spatial coordinate and three-velocity components), electromagnetic particle simulation code with full ion and electron dynamics, we have studied the acceleration of heavy ions by a nonlinear magnetosonic wave in a multi-ion-species plasma. First, we describe the mechanism of heavy ion acceleration by magnetosonic waves. We then investigate this by particle simulations. The simulation plasma contains four ion species: H, He, O, and Fe. The number density of He is taken to be 10% of that of H, and those of O and Fe are much lower. Simulations confirm that, as in a single-ion-species plasma, some of the hydrogen can be accelerated by the longitudinal electric field formed in the wave. Furthermore, they show that magnetosonic waves can accelerate all the particles of all the heavy species (He, O, and Fe) by a different mechanism, i.e., by the transverse electric field. The maximum speeds of the heavy species are about the same, of the order of the wave propagation speed. These are in good agreement with theoretical prediction. These results indicate that, if high-energy ions are produced in the solar corona through these mechanisms, the elemental compositions of these heavy ions can be similar to that of the background plasma, i.e., the corona.     

Ion acoustic solitary waves in bi-ion plasma with superthermal electrons

Weak ion-acoustic solitary waves (IASWs) in unmagnetized plasmas having two-fluid ions and kappa-distributed electrons are considered. The effects of electron suprathermality, warm ion temperature and polarity on the nonlinear properties of these IASWs are analyzed. It is found that our present plasma model may support compressive as well as rarefactive solitary structures.     

Cross-scale coupling at a perpendicular collisionless shock

A full particle simulation study is carried out on a perpendicular collisionless shock with a relatively low Alfven Mach number (M_A = 5). Recent self-consistent hybrid and full particle simulations have demonstrated ion kinetics are essential for the non-stationarity of perpendicular collisionless shocks, which means that physical processes due to ion kinetics modify the shock jump condition for fluid plasmas. This is a cross-scale coupling between fluid dynamics and ion kinetics. On the other hand, it is not easy to study cross-scale coupling of electron kinetics with ion kinetics or fluid dynamics, because it is a heavy task to conduct large-scale full particle simulations of collisionless shocks. In the present study, we have performed a two-dimensional (2D) electromagnetic full particle simulation with a “shock-rest-frame model”. The simulation domain is taken to be larger than the ion inertial length in order to include full kinetics of both electrons and ions. The present simulation result has confirmed the transition of shock structures from the cyclic self-reformation to the quasi-stationary shock front. During the transition, electrons and ions are thermalized in the direction parallel to the shock magnetic field. Ions are thermalized by low-frequency electromagnetic waves (or rippled structures) excited by strong ion temperature anisotropy at the shock foot, while electrons are thermalized by high-frequency electromagnetic waves (or whistler mode waves) excited by electron temperature anisotropy at the shock overshoot. Ion acoustic waves are also excited at the shock overshoot where the electron parallel temperature becomes higher than the ion parallel temperature. We expect that ion acoustic waves are responsible for parallel diffusion of both electrons and ions, and that a cross-scale coupling between an ion-scale mesoscopic instability and an electron-scale microscopic instability is important for structures and dynamics of a collisionless perpendicular shock.     

Diffusion of a multi-component plasma

Diffusion in a weakly ionized plasma composed of negative ions as well as positive ions is examined using appropriate linearized fluid equations. For initial, electrically neutral, density perturbations of the form exp(ikx) the diffusion process is characterized by electrical non-neutrality and by three stages or time scales. For equal positive and negative ion diffusion coefficients these stages are in general (1) equilibration of the electron gas so that pressure gradient and electric forces are balanced (2) ambipolar-like diffusion of all three species, and concluding with (3) free ion diffusion. The details of the process are governed by the product kλ_e (wave number times electron Debye length) and the ambient ratio of negative ion to electron number density. Numerical and analytic results for separate positive and negative diffusion coefficients show added complexity which is briefly described. These results or the more complete numerical solutions find application to the lower D region of the ionosphere.     

Shear flow driven counter rotating vortices in an inhomogeneous dusty magnetoplasma

The coupling of Shukla-Varma (SV) and convective cell modes is discussed in the presence of non-Boltzmannian electron response and parallel equilibrium shear flow. In the linear case, a new dispersion relation is derived and analyzed. It is found that the coupled SV and convective cell modes destabilize in the presence of electron shear flow. On the other hand, in the nonlinear regime, it is shown that Shukla-Varma mode driven counter rotating vortices can be formed for the system under consideration. It is found that these vortices move slowly by comparison with the ion acoustic or electron drift-wave driven counter rotating vortices. The relevance of the present investigation with regard to space plasmas is also pointed out.     

Electromagnetic Ion Cyclotron Waves in Multi-Ions Hot Anisotropic Plasma in Auroral Acceleration Region-Particle Aspect Approach

Using particle aspect approach, the effect of multi-ions densities on the dispersion relation, growth rate, perpendicular resonant energy and growth length of electromagnetic ion cyclotron wave with general loss-cone distribution function in hot anisotropic multi-ion plasma is presented for auroral acceleration region. It is observed that higher He⁺ and O⁺ ions densities enhance the wave frequency closer to the H⁺ ion cyclotron frequency and growth rate of the wave. The differential heating of He⁺ ions perpendicular to the magnetic field is enhanced at higher densities of He⁺ ions. The waves require longer distances to achieve observable amplitude by wave-particle interactions mechanism as predicted by growth length. It is also found that electron thermal anisotropy of the background plasma enhances the growth rate and reduces the growth length of multi-ions plasma. These results are determined for auroral acceleration region.     

Radio emission of fast cosmic ions

It is usually assumed that the ions of cosmic rays contribute nothing to the observable electromagnetic radiation. However, this is true only when these ions are moving in a vacuum or a quiet (nonturbulent) plasma. In the case of fast ions in a turbulent plasma, there is an effective nonlinear mechanism of radiation which is discussed in this paper. The fast ion (relativistic or nonrelativistic) moving in the plasma creates a polarization cloud around itself which also moves with the particles. The turbulent plasma waves may scatter on the moving electric field of this polarization cloud. In the process of this scattering an electromagnetic wave with frequency (2.7) is generated. Let ₁ and k₁ be the frequency and wave vector of turbulent plasma waves,V is the velocity of the ion, and is the angle between the wave vector of electromagnetic radiation and the direction of the ion velocity. The method of calculating the probability of the conversion of plasma waves (k₁) into electromagnetic waves (k) by scattering on an ion with velocityV is described in detal in Section 2 (Equation (2.14)).The spectral coefficients of spontaneous radiation in the case of scattering of plasma waves on polarization clouds created by fast nonrelativistic ions are given in (3.6) for an ion energy distribution function (3.4) and in (3.8) for more general evaluations. The Equations (3.9)–(3.13) describe the spectral coefficients of spontaneous emission for different modes of plasma turbulence (Langmuir (3.9), electron cyclotron in a weak (3.10) or strong (3.11) magnetic field and ion acoustic (3.12)–(3.13) waves). The coefficients of reabsorption or induced emission are given by Equations (3.14) and (3.16)–(3.19). There is a maser effect in the case of scattering of plasma waves on a stream of ions. The effective temperature of the spontaneous emission is given by Equation (3.15). The spectral coefficients of radiation due to scattering of plasma waves on relativistic ions are calculated in the same manner (Equations (4.14)–(4.15)). The total energy loss due to this radiation is given in Equations (4.23)–(4.25). The coefficients of induced emission are given in (4.26)–(4.28).The results are discussed in Section 5. It is shown that the loss of energy by nonlinear plasma radiation is much smaller than the ionization loss. However, the coefficients of synchrotron radiation of electrons and nonlinear radiation of ions under cosmic conditions may be comparable in the case of a weak magnetic field and fairly low frequencies (5.5)–(5.6). Usually the spectrum of nonlinear plasma radiation is steeper than in the case of synchroton radiation. Equation (5.10) gives the condition for nonlinear radiation to prevail over thermal radiation.Translated by D. F. Smith.     

Thermal response properties of the Earth's ionospheric plasma

The thermal response of the Earth's ionospheric plasma is calculated for various suddenly applied electron and ion heat sources. The time-dependent coupled electron and ion energy equations are solved by a semi-automatic computational scheme that employs Newton's method for coupled vector systems of non-linear parabolic (second order) partial differential equations in one spatial dimension. First, the electron and composite ion energy equations along a geomagnetic field line are solved with respect to a variety of ionospheric heat sources that include: thermal conduction in the daytime ionosphere; heating by electric fields acting perpendicular to the geomagnetic field line; and heating within a stable auroral red are (SAR-arc). The energy equations are then extended to resolve differential temperature profiles, first for two separate ion species (H⁺, O⁺) and then for four separate ion species (H⁺, He⁺, N⁺, O⁺) in addition to the electron temperature. The electron and individual ion temperatures are calculated for conditions within a night-time SAR-arc excited by heat flowing from the magnetosphere into the ionosphere, and also for typical midlatitude daytime ionospheric conditions. It is shown that in the lower ionosphere all ion species have the same temperature; however, in the topside ionosphere above about 400 km, ion species can display differential temperatures depending upon the balance between thermal conduction, heating by collision with electrons, cooling by collisions with the neutrals, and energy transfer by inter-ion collisions. Both the time evolution and steady-state distribution of such ion temperature differentials are discussed.The results show that below 300km both the electrons and ions respond rapidly (<30s) to variations in direct thermal forcing. Above 600 km the electrons and ions display quite different times to reach steady state, depending on the electron density: when the electron density is low the electrons reach steady state temperatures in 30 s, but typically require 700 s when the density is high; the ions, on the other hand, reach steady state in 700 s when the density is high, and 1500–2500 s when the density is low. Between 300 and 600 km, a variety of thermal structures can exist, depending upon the electron density and the type of thermal forcing; however steady state is generally reached in 200–1000 s.     

Ion-cyclotron instability and electron acceleration in coronal loops

Quasi-electrostatic electron and ion-cyclotron instabilities are studied. The result indicates that the higher harmonic ion cyclotron instabilities (ICI) can be excited while the fast ions produced from reconnection are injected into a coronal loop. Part of the energetic ions can be dragged out of the magnetic mirror turning points and a negative plasma potential is generated. The plasma potential may directly accelerate the electrons up to the relativistic velocity within a short time. This acceleration is similar to the processes occurring in the magnetic mirror devices of controlled thermonuclear fusion. The spectrum and flux of accelerated electrons have also been obtained. Some observational results during the solar flare might be explained by this acceleration mechanism.     

Roles of positively charged heavy ions and degenerate plasma pressure on cylindrical and spherical ion acoustic solitary waves

The properties of heavy-ion-acoustic (HIA) solitary structures associated with the nonlinear propagation of cylindrical and spherical electrostatic perturbations in an unmagnetized, collisionless dense plasma system has been investigated theoretically. Our considered model contains degenerate electron and inertial light ion fluids, and positively charged static heavy ions, which is valid for both of the non-relativistic and ultra-relativistic limits. The Korteweg-de Vries (K-dV) and modified K-dV (mK-dV) equations have been derived by employing the reductive perturbation method, and numerically examined in order. It has been found that the effect of degenerate pressure and number density of electron and inertial light ion fluids, and positively charged static heavy ions significantly modify the basic features of HIA solitary waves. It is also noted that the inertial light ion fluid is the source of dispersion for HIA waves and is responsible for the formation of solitary waves. The basic features and the underlying physics of HIA solitary waves, which are relevant to some astrophysical compact objects, are briefly discussed.     

Effect of ion temperature on small-amplitude ion acoustic solitons in a magnetized ion-beam plasma in presence of electron inertia

Existence of both compressive and rarefactive solitons are found to exists in a magnetized plasma model consisting of ions, electrons and positive ion beams using the Korteweg-de Vries (KdV) equation. Both fast and slow modes are found to exist due to the presence of ion temperature in the plasma. Moreover, the amplitude of the soliton decreases with an increase in temperature for Q′ (, beam-ion mass to warm-ion mass ratio) >2 and the amplitude becomes maximum when the wave propagates parallel with the direction of the magnetic field. The investigation further revealed that though both compressive and rarefactive solitons exist for slow mode, only compressive soliton exist for the fast mode.