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Expansion of solar wind into the interplanetary space generates temperature anisotropy that cannot be justified by adiabatic fluid theory. Kinetic instabilities driven by the interplay between electrons and protons temperature anisotropy may be operative in order to explain the actual state of solar wind reported by satellite observations. Based on the temperature anisotropy, T ⊥ / T ∥ , and alternative different plasma beta, β, regimes of solar wind species, we investigate the unified wave spectrum where left-hand polarized electromagnetic proton cyclotron and electron firehose instabilities may co-exist or transit with each other. Linear stability analysis catches the co-existence/transition of these instabilities in the different propagation domain. A moment-based quasilinear approach is adopted to highlight the feedback effects of these instabilities on the initial distributions and also to validate the transition during the non-linear (or quasilinear) time-evolution of the instabilities. Looking at the solar wind observations, we assume a bi-Maxwellian dual core-halo electron and proton model that allows solar wind species temperatures to vary in time t in addition. By incorporating the radial expansion effects and inhomogeneities, our present findings may be applicable to the First Solar Parker Probe observations. [ABSTRACT FROM AUTHOR]

It is pointed out that the criterion ω p e ≪ ω p + , ω p − (where ωpj is the plasma oscillation frequency of jth species and j = e, +, −) presented to define pure pair-ion plasma must also be fulfilled to ignore electron dynamics in positive-negative ion plasma. It is also suggested that the potassium (K+) plasma having negative ions of perfluoromethylcyclohexane (C 7 F 14 −) produced in Q-machine seems to have a significant number density of electrons; therefore, ion acoustic waves (IAW) may also exist. If T ± < T e and ions have field-aligned shear flow, the fluid theory predicts that the IAWs will be excited. The dimensions of experimentally produced plasma are small; therefore, the local theory is applicable only approximately. Since observations show that T e ≃ T ± in the laboratory performed experiments with positive-negative ions, the kinetic theory is also used to look for electron current-driven IAWs. Kinetic theory predicts that IAWs will be highly damped if electrons flow antiparallel to B0 in opposite direction with respect to positive ions. On the other hand, if electrons flow along B0 as is the case of ionospheric plasma, then IAWs become unstable. Thus, field-aligned shear flow of ions and parallel electron current can produce IAWs both in laboratory and astrophysical electron positive negative ion plasmas. [ABSTRACT FROM AUTHOR]

The linear and nonlinear properties of ion-acoustic rogons and associated modulational instability (MI) are studied in an unmagnetized dense electron-ion plasma, containing degenerate trapped/untrapped electrons and classical adiabatic ions. Solving the quantum hydrodynamic equations by using the standard multiscale reductive perturbation technique, a nonlinear Schrödinger equation is derived, which admits potential envelopes to be stable (unstable) against the perturbations for PQ < 0 (PQ > 0) . Here, P and Q are the dispersion and nonlinearity coefficients, respectively. It is numerically shown that for the vanishing ionic temperature ratio (σ = 0) , the parametric regime at perturbation wavelengths λ ≥ 2.5 λ eff (λ ≤ 2.5 λ eff ) is always modulationally stable (unstable); here, λeff is the effective screening length. Moreover, the finite ionic temperature (T i ≤ 10 eV) restores the modulational stability at relatively short wavelengths by confining MI within the perturbation range 4.5 λ eff ≤ λ ≤ 1.3 λ eff. The parameter Θ (= T e / 2 2 μ) shows the impact of the untrapped electrons which not only enhances (reduces) the angular frequency (group speed) of the envelope but also piles up the wave crests (energy) to produce the MI. Furthermore, due to degenerate trapped electrons, the instability domain gets widened in the limit PQ > 0 and leads to the onset of MI and unstable excitations. The study has important results for understanding the mechanism of MI and unstable modes in the context of astrophysical environments (white dwarfs, neutron stars, etc.,) and high density experiments. [ABSTRACT FROM AUTHOR]

Using kinetic approach, the effect of electron-ion collisions on Weibel instability has been investigated for three different types of anisotropic distribution functions (i.e., bi-kappa, bi-Maxellian, and product bi-kappa). It is found that the presence of electron-ion collisions has a negative effect on the growth rate of Weibel instability. By using analytical analysis, it has been found that the growth rate of the collisional plasma becomes negative if the electron-ion collision frequency becomes higher than the growth rate of the Weibel instability for a collisionless plasma while keeping all the other parameters same. The impact of electron-ion collisions has also been studied on the temperature anisotropy parameter τ(=T⊥/T‖)τ(=T⊥/T‖) threshold required for making the growth rate of the Weibel instability positive for all the three distribution functions. The illustrations show that for higher spectral index κ‖=κ>4κ‖=κ>4, the temperature anisotropy threshold is same for all the three distribution functions; however, for lower κ‖=κ<4κ‖=κ<4, the threshold conditions are different for the bi-kappa as compared to those found for the other two distribution functions. The boundaries between the stable and unstable regions of bi-kappa and product bi-kappa distributions have been found in the presence of collisions. In the presence of collisions, the boundary curve for product bi-kappa is similar to that we get in the absence of collisions. However, the temperature anisotropy threshold parameters are higher for collisional plasma as compared to those obtained for the collisionless plasma. The boundary curve for bi-kappa distribution function in the presence of collisions is significantly different from the boundary curve formed in the absence of collisions. In the presence of collisions, the temperature anisotropy threshold increases very rapidly when the spectral index is <2. [ABSTRACT FROM AUTHOR]

The dynamics of obliquely propagating ion-acoustic (IA) waves in the presence of ionic pressure anisotropy and electron trapping effects is studied in a dense magnetoplasma, containing degenerate relativistic trapped electrons and dynamical (classical) ions. By using the plane wave solution, a modified linear dispersion relation for IA waves is derived and analyzed with different limiting cases and various plasma parameters both analytically and numerically. For nonlinear analysis, a reductive perturbation technique is employed to obtain a Zakharov-Kuznetsov equation involving the weakly nonlinear IA excitations. It is shown that the electron thermal correction and ionic pressure anisotropy strongly modify the wave amplitudes and width attributed to weakly nonlinear IA waves. The stability criterion for stable/unstable solitary pulses is also discussed with variations of angle (β) and temperature ratio (σ). A reduction and domain splitting of unstable excitations into sub-domains with stable and unstable potential pulses are pointed out for electron temperature ratio in the range of 0.01 < σ < 0.3 for degenerate relativistic trapped electrons. Moreover, the ionic pressure anisotropy also considerably affects the stability of solitary potentials in the non-relativistic and ultra-relativistic regimes. The obtained results might be useful for understanding the nonlinear dynamics and propagation characteristics of waves in superdense plasmas, in the environments of white dwarfs and neutron stars, where the electron thermal and ionic pressure anisotropy effects cannot be ignored. [ABSTRACT FROM AUTHOR]

Dynamics of shear flow modified ion acoustic wave is investigated assuming electrons to follow q-nonextensive and Cairns distribution functions. A modified linear dispersion relation and electrostatic KdV solitons are analyzed. Results are illustrated considering solar wind and F-region ionospheric plasmas. Effects of non-Maxwellian distribution of electrons on the amplitude and the width of solitons are pointed out in the presence of field-aligned inhomogeneous flow. [ABSTRACT FROM AUTHOR]

Large-amplitude electron acoustic (EA) waves and shocklets are investigated in a two-temperature electron plasma. For this purpose, dynamical cold electrons are described by the fully nonlinear continuity and momentum equations, while superthermal (hot) inertialess electrons are described by the κ-distribution function with a neutralizing background of static positive ions. The fluid equations along with a quasineutrality equation are solved to obtain a set of two characteristic wave equations that admit analytical and numerical solutions. It is shown that variation due to hot electron superthermality and hot-to-cold electron density ratio strongly affects the profiles of nonlinear EA structures in terms of negative potential, cold electron velocity and density. In particular, at time τ = 0; symmetric solitary pulses are formed, which develop into oscillatory shocklets with the course of time. Our results should be useful for understanding solitary excitations and associated nonstationary large-amplitude shocklets in laboratory κ-distributed plasmas, where superthermal (hot) energetic electrons exist. [ABSTRACT FROM AUTHOR]

Ion-acoustic solitary waves (IASWs) are investigated in a plasma having a cold positron beam fluid, electrons following a vortex-like distribution with entropic index q, and dynamic ions. Using a standard procedure, a pseudo-potential energy equation is derived. The presence of nonextensive q-distributed trapped electrons and cold positron beam has been shown to influence the small amplitude soliton structure quite significantly. From the analysis of our results, it is shown that compressive IASWs are supported in this plasma model. As the real plasma situations are observed with plasma species having a relative flow, our present analysis should be beneficial for comprehending the electrostatic solitary structures observed in fusion plasma devices and positron winds observed in astrophysical plasmas. [ABSTRACT FROM AUTHOR]

We study the acceleration and trapping of both negative and positive charged particles in the quasilinear donut wake (created by a Laguerre Gauss laser pulse). The motion of test charged particles is studied in a two-dimensional wakefield. Once the charged particles are completely trapped in the wakefield, the dynamics will be determined. It is shown that for definite parameters of the problem, a positron bunch could be trapped and accelerated and also well compressed in the first-half bucket of the donut wake. The results also show the possibility of trapping and acceleration of a hollow electron bunch with modified longitudinal and transverse properties. It is proved that electrons could be trapped just as a hollow bunch in the quasi-linear donut wake. [ABSTRACT FROM AUTHOR]

It is shown that the inhomogeneous field-aligned flow of heavier ions into the stationary plasma of the upper ionosphere produces very low frequency (of the order of a few Hz) electrostatic unstable ion acoustic waves (IAWs). This instability is an oscillatory instability unlike D'Angelo's purely growing mode. The growth rate of the ion acoustic wave (IAW) corresponding to heavier ions is due to shear flow and is larger than the ion Landau damping. However, the ion acoustic waves corresponding to non-flowing lighter ions are Landau damped. It is found that even if D'Angelo's instability condition is satisfied, the unstable mode develops its real frequency in this coupled system. Hence, the shear flow of one type of ions in a bi-ion plasma system produces ion acoustic wave activity. If the density non-uniformity is taken into account, then the drift wave becomes unstable. The coupled nonlinear equations for stationary ions "a," flowing ions "b," and inertialess electrons are also solved using the small amplitude limit. The solutions predict the existence of the order of a few kilometers electric field structures in the form of solitons and vortices, which is in agreement with the satellite observations. [ABSTRACT FROM AUTHOR]

Linear and nonlinear electrostatic ion acoustic waves in a weakly relativistic magnetorotating plasma in the presence of non-Maxwellian electrons and warm ions have been examined. The system under consideration has yielded two solutions, namely, the fast and slow acoustic modes which have been observed to depend on the streaming velocity, ion to electron temperature ratio, and the nonthermality parameter of the non-Maxwellian electrons. Using the multiple time scale analysis, we have derived the three dimensional nonlinear Zakharov-Kuznetsov equation and also presented its solution. Both compressive and rarefactive solitary structures have been found in consonance with the satellite observations. It has been observed that although the linear dispersion relation gives both fast and slow ion acoustic waves, the solitary structures form only for the fast acoustic mode. The dependence of the characteristics of the solitary structures on several plasma parameters has also been explored. The present investigation may be beneficial to understanding the rotating plasma environments such as those found in the planetary magnetospheres of Saturn and Jupiter. [ABSTRACT FROM AUTHOR]

Coupling of drift vortex and the ion acoustic modes in the linear and nonlinear regimes are investigated with sheared ion flow perpendicular to the ambient magnetic field in a plasma comprising of hot ions and nonthermal population of electrons. In this regard, generation of nonlinear vortex structures in the presence of kappa, Cairns, and q-nonextensive electron distributions are investigated in detail, and comparison with the Maxwellian distribution is also made. The appositeness of the present investigation in the matter of auroral F-region is also pointed out. [ABSTRACT FROM AUTHOR]

Bernstein mode for a relativistic degenerate electron plasma is investigated. Using relativistic Vlasov-Maxwell equations, a general expression for the conductivity tensor is derived and then employing Fermi-Dirac distribution function a generalized dispersion relation for the Bernstein mode is obtained. Two limiting cases, i.e., non-relativistic and ultra-relativistic are discussed. The dispersion relations obtained are also graphically presented for some specific values of the parameters depicting how the propagation characteristics of Bernstein waves as well as the Upper Hybrid oscillations are modified with the increase in plasma number density. [ABSTRACT FROM AUTHOR]

Streaming instabilities in electron-positron-ion plasmas are investigated using kinetic approach in several different limits. The effects of the variation of background temperatures of electrons Teo and positrons Tpo on the growth rates are also presented for the case of ion beam streaming into electron-positron plasmas and positrons beam streaming into electron-ion plasmas. It is noticed that the increase of number density of positrons gives a destabilizing trend to the electrostatic perturbations in the system. [ABSTRACT FROM AUTHOR]

Presents a numerical solution for the expansion of a plasma consisting of positive ions, negative ions, and electrons into a vacuum. Expected self-similar expansion found in a quasineutral plasma expansion model; Acceleration of a burst of positive ions into the vacuum and a burst of negative ions into the plasma.

Nonlinear dissipative structures are studied in one and two dimensions in nonuniform magnetized plasmas with non-Maxwellian electrons. The dissipation is incorporated in the system through ion-neutral collisions. Employing the drift approximation, nonlinear drift waves are derived in 1D, whereas coupled drift-ion acoustic waves are derived in 2D in the weak nonlinearity limit. It is found that the ratio of the diamagnetic drift velocity to the velocity of nonlinear structure determines the nature (compressive or rarefactive) of the shock structure. The upper and lower bounds for velocity of the nonlinear shock structures are also found. It is noticed that the existence regimes for the drift shock waves in one and two dimensions for Cairns distributed electrons are very distinct from those with kappa distributed electrons. Interestingly, it is found that both compressive and rarefactive shock structures could be obtained for the one dimensional drift waves with kappa distributed electrons. [ABSTRACT FROM AUTHOR]

The Korteweg-de Vries Burgers ðKdVBÞ-like equation is derived to study the characteristics of nonlinear propagation of ion acoustic solitions in a highly relativistic plasma containing relativistic ions and nonextensive distribution of electrons and positrons using the well known reductive perturbation technique. The KdVB-like equation is solved employing the Bernoulli's equation method taking unperturbed positron to electron concentration ratio, electron to positron temperature ratio, strength of nonextensivity, ion kinematic viscosity, and highly relativistic streaming factor. It is found that these parameters significantly modify the structures of the solitonic excitation. The ion acoustic shock profiles are observed due to the influence of ion kinematic viscosity. In the absence of dissipative term to the KdVB equation, compressive and rarefactive solitons are observed in case of superthermality, but only compressive solitons are found for the case of subthermality. [ABSTRACT FROM AUTHOR]

A new scheme for acceleration and focusing of protons via an improved parabolic double concave target irradiated by an ultraintense laser pulse is proposed. When an intense laser pulse illuminates a concave target, the hot electrons are concentrated on the focal region of the rear cavity and they form a strong space-charge-separation field, which accelerates the protons. For a simple concave target, the proton energy spectrum becomes very broad outside the rear cavity because of transverse divergence of the electromagnetic fields. However, particle-in-cell simulations show that, when the concave target has an extended rear, the hot electrons along the wall surface induce a transverse focusing sheath field, resulting in a clear enhancement of proton focusing, which makes the lower proton energy spread, while, leads to a little reduction of the proton bunch peak energy. [ABSTRACT FROM AUTHOR]

A scheme of a symmetric parabolic concave target irradiated by an ultraintense laser for efficient proton acceleration is proposed and involved problem is studied by using two-dimensional particle-in-cell (PIC) simulations. Results indicate that on one hand, the laser field is focused by the front parabolic concave surface of target and, on the other hand, more energetic hot electrons will traverse to the rear surface of target due to concave shape. The space-charge-separation field, induced by those hot electrons escaping form parabolic concave rear surface of target, can accelerate protons to relatively high energy with narrow energy spread. The dependence of the efficiency of proton acceleration on the target parameters is examined, and the optimal target parameters are obtained. Particle-in-cell simulations show that the proton peak energy and energy spread are greatly enhanced when the target parameters are chosen optimal, for example, a proton bunch with the maximum energy ∼27.5 MeV and energy spread ∼7% can be generated. Some implications of our results to experiments and comparisons with the other works are also discussed briefly. [ABSTRACT FROM AUTHOR]

A transverse gauss shape magnetic field with wide width is proposed for collimating the fast relativistic electron beam in laser irradiating plasmas, which is highlighted by the twodimensional particle-in-cell simulations, in particular, the effects of this magnetic field on the production and transport of fast electron beam. When the axial magnetic field is also present, it is found that the energy density of fast electrons can be enhanced greatly. For example, in the presence of 30MG axial magnetic field, it is enhanced by 3-4 times when the amplitude of the applied transverse magnetic field lies within the optimal regime 200-300MG comparable to that without the transverse magnetic field. Meanwhile, the divergence angle of the electron beam can be controlled and even decreased a little due to the better sandwich structure of the overall weakening magnetic field. The study implies that the proposed transverse magnetic field is helpful to obtain the high quality electron beam which is beneficial to the fast ignition in inertial confinement fusion. [ABSTRACT FROM AUTHOR]

In the present work, we have discussed the effects of adiabatic trapping of electrons on obliquely propagating Alfvén waves in a low β plasma. Using the two potential theory and employing the Sagdeev potential approach, we have investigated the existence of arbitrary amplitude coupled kinetic Alfvén-acoustic solitary waves in both the sub and super Alfvénic cases. The results obtained have been analyzed and presented graphically and can be applied to regions of space where the low β assumption holds true. [ABSTRACT FROM AUTHOR]