Superthermal Plasmas Research Articles

Effects of Superthermal Plasmas on Hiss Wave‐Driven Scattering Loss of Radiation Belt Electrons

AbstractPlasmaspheric hiss plays an important role in the loss of radiation belt electrons via cyclotron resonant interactions. The cold plasma approximation is widely used in the evaluation of hiss‐driven electron losses, which however can break down during disturbed periods of geomagnetic storms and substorms. The kappa particle velocity distribution, characterized by a pronounced high‐energy tail, is well‐established to model the profile of superthermal plasma under disturbed geomagnetic conditions. In the present study, by calculating the electron bounce‐averaged pitch angle diffusion coefficients with kappa plasma dispersion relations, we investigate the sensitivity of hiss‐induced cyclotron‐resonant electron scattering loss to the spectral index κ under a variety of superthermal plasma conditions. Our results demonstrate that, with increasing κ, the diffusion coefficients of ∼20–100 keV radiation belt electrons significantly decrease at lower pitch angles and increase at higher pitch angles. In contrast, for electrons at higher energies, the diffusion coefficients tend to increase at lower pitch angles and decrease at relatively higher pitch angles. We also find that decrease of L‐shell and increase of α* and temperature anisotropy tend to weaken the hiss‐driven pitch angle scattering efficiency of electrons at energies from tens to hundreds of keV with a dip at ∼30–50 keV, while the scattering of higher energy electrons can be enhanced. This study confirms the important role of superthermal plasmas in the hiss‐driven electron loss processes and should be carefully incorporated in future modeling of radiation belt electron dynamics.

Parametric analysis of dust ion acoustic waves in superthermal plasmas through non-autonomous KdV framework

In the presence of superthermal plasma, propagation of non-linear dust ion acoustic waves has been studied in the framework of the Damped Forced Korteweg–de Vries (DFKdV) Equation. A feasible range is obtained for the existence of the solitary wave solutions in terms of the spectral index, and the unaffected dust-to-ion density ratio (denoted by κ and μ, respectively). It is observed that the transition of solitary wave structures from compressive to rarefactive can be completely determined by mainly these two parameters. The effects of all other parameters involved in the model, namely, the strength (f0) and frequency (ω) of the external periodic force, and damping coefficient (νid0) are studied using the bifurcation analysis; f0 and ω play a crucial role in the periodic and chaotic motions in the system. We also obtained certain critical values of the key parameters involved in the model for which the model exhibits periodic, quasi-periodic and chaotic behaviour.

Analysis of solitons structure of the damped KdV equation arising in superthermal plasmas: Application of homotopy analysis method

AbstractThe aim of the proposed work is to analyze the soliton structures of dust‐ion acoustic waves obtained in the framework of the Korteg‐de Vries (KdV) equation with the presence of a damping term. The concept of electron acoustic solitary wave in an unmagnetized plasma consisting of superthermal electrons has been taken into consideration. The KdV equation with the presence of a damping term has been derived with the help of the reductive perturbation technique and solved by using the well‐known homotopy analysis method. The considered method approximates all problems in a straightforward and simplified manner. The method computes the series solution efficiently and provides a simple way to ensure its convergence. The approximate analytical solution obtained from the present analysis is compared with available results in the literature for a different choice of pertinent parameters. The upshots specified that the amplitude of solitary waves increases for increasing values of the damping parameter. This study would in a way to demonstrate the potential and effectiveness of the homotopy analysis method to evaluate the various kinds of nonlinear equations arising in the soliton theory.

Driven ion acoustic wave nonlinearities in superthermal electron plasmas

The fluid nonlinearities of driven ion acoustic waves (IAWs) in superthermal electron plasmas are investigated by fluid theory and one-dimensional fluid simulation. A kappa velocity distribution function is used to model superthermal electrons. Under the condition of small wave amplitudes, simulation results are presented to verify the conclusion of fluid theory, showing that the presence of superthermal electrons leads to stronger harmonic generation and larger nonlinear frequency shifts of IAWs. In addition, the growth rate and threshold of the IAW decay instability from simulations are well predicted by a simple three-wave fluid theory. It is shown that the nonlinear frequency shift has a significant effect on IAW decay, and for a larger population of superthermal electrons, the IAW decay has a smaller onset threshold and threshold range.

Dynamical behaviour of nonlinear structures in superthermal plasmas associated with external periodic force

Dynamical behaviour of nonlinear structures in superthermal plasmas associated with external periodic force

Studies on the Dust–Ion–Acoustic Solitary Wave in Planar and Non-Planar Super-Thermal Plasmas with Trapped Electrons

Studies on the Dust–Ion–Acoustic Solitary Wave in Planar and Non-Planar Super-Thermal Plasmas with Trapped Electrons

Propagation of nonlinear excitations of dust acoustic waves by a moving charged object in superthermal plasmas

Propagation of nonlinear excitations of dust acoustic waves by a moving charged object in superthermal plasmas

Ion temperature gradient mode driven solitons and shocks in superthermal plasma

An analysis of the ion temperature gradient driven mode solitary and shock waves in superthermal plasma is presented. Based on the observation in linear region it is shown that the phase velocity of the mode has strong dependency on superthermal particles population and on ion temperature. Linear dispersion relation is reduced to two different results by considering different limiting cases: (i) when superthermality (κ) is ignored in the system and (ii) when the fluctuations are caused by E×B convection only. In nonlinear regime we in our investigations observe that, nonlinear waves are strongly modified in superthermal plasmas. Furthermore, the different parametric analysis clearly shows that speed and the energy of these nonlinear structures driven by ion temperature gradient modify. These parametric analysis are quite constructive, which in turns may provide help in future designing of plasma fusion devices. The present investigation of this article may have its relevance to astrophysical and laboratory plasma.

Effects of Superthermal Plasmas on the Linear Growth of Multiband EMIC Waves

Abstract Observations show that particle velocity distributions in space plasmas generally exhibit a non-Maxwellian high-energy tail that can be well fitted with kappa distributions. To better understand the correlation between realistic particle velocity distributions and plasma wave excitation, we investigate the linear cyclotron instability of multiband electromagnetic ion cyclotron (EMIC) waves in a kappa plasma containing hot anisotropic protons, which provides the free energy for the wave growth. We find that the effects of superthermal plasmas on EMIC wave instability have a strong dependence on the emission band, temperature anisotropy A hp, and parallel beta β hp of hot protons. For H+ and He+ band EMIC waves, the maximum growth rates exhibit distinct behaviors with the variation of the spectral index κ of kappa distributions for different A hp values. The maximum growth rates decrease with increasing κ-value for low A hp and increase with increasing κ-value for high A hp. For O+ band waves, the effects of superthermal plasmas on the maximum growth rate are strongly controlled by β hp. For low β hp, the growth rate decreases monotonically with increasing κ-value for all A hp. For high β hp, increase of κ-value tends to enhance the wave growth for intermediate A hp and to suppress the wave growth otherwise. Our results also indicate that the presence of a high-energy tail tends to decrease the real frequency corresponding to the maximum growth rate for all three bands. While the minimum electron resonant energy for O+ band EMIC waves decreases as the κ-value increases, the minimum electron resonant energies for H+ and He+ band waves remain unaffected.

Effects of positron and two ion masses on the critical behaviour in superthermal collisional plasmas

The Wave time dissipation characteristic of plasma solitons in a two ion-component fluids and two Kappa distributed electrons and positrons have been investigated. The damped-two dimensional Kadomtsev-Petviashvili (DKP) equation which embodied all wave damping information has been gained. The nonlinear condition for DKP criticality is calculated in the form of MDKP equation. By using D-F Earth-ionosphere regime parameters, the effects of the index of superthermality, collision frequencies, electron density, positron density and ionic mass ratios on the solitary formation of both structures of rarefactive (compressive) and critical waves are examined. It is a rating mention to signify that the outcomes performed here are applicable in the plasma of Earth’s ionosphere.

Excitation and Formation Conditions of Monotonic Shock Waves in Magnetized Plasmas with Superthermality Distributed Electrons

Nonlinear excitation and the properties of ion-acoustic shock waves (IASWs) in a magnetoplasma model composed of viscous ions with two-temperature superthermality distributed electrons are studied by employing the well-known reductive perturbation analysis to obtain a nonlinear Zakharov-Kuznetsov-Burgers equation (ZKBE), which admits the excitation of nonlinear IASWs in superthermal plasmas. Applying the tanh method, we discuss the solutions of the ZKBE. The asymptotic behavior and the stability of the analytical shock wave solution are studied. In general, nonlinear ion-acoustic disturbances are found analytically to exhibit only monotonic shock structures in the proposed model. For different situations, the effects of the dispersion and the dissipation coefficients on the profiles of the shock structures are discussed. The findings here demonstrate that the effective features of nonlinear IASWs depend strongly on the dispersion and the dissipation coefficients, which include physical parameters such as the superthermality of cold electrons, the cold superthermal electron-to-ion number density ratio, the ion kinematic viscosity and the ion cyclotron frequency. The current work may be helpful for an advanced comprehension of the physical nature of shock waves in astrophysical plasma situations.

Effects of wave potential on electron holes in thermal and superthermal space plasmas

Observations from various interplanetary and other spacecraft missions evince that superthermal distributions are omnipresent in the solar wind and near Earth's plasma environment. These observations confirm the presence of coherent bipolar electric field pulses. In phase space, these electric field structures are observed as electron holes (EHs) or ion holes. Trapping of particles in a potential well causes the formation of such structures and is generally studied using the Bernstein-Greene-Kruskal approach. The literature on these structures encompasses the trapped electron distribution function and physically plausible regions. In this paper, we focus on the effects of the width and amplitude of wave potential on electron trapping in thermal and superthermal plasmas. It can be observed that both an increase in the width and the amplitude of wave potential cause an augmentation in the trapping of particles. The amplitude plays a dominant role in the trapping of maximum energetic particles, whereas the width plays a role in deciding the density of particles at the center of the EHs. We found that there exists an upper limit for the stability region of EHs defined by the width-amplitude relation. Additionally, it is noticed that the superthermal plasma does not impose restriction on the presence of electron holes with a width less than the electron Debye length.

Cylindrical Damped Solitary Propagation in Superthermal Plasmas

Wave properties of damped solitons in a collisional unmagnetized four-components dusty fluid plasma system contains superthermal distributed electrons, mobile ions, and negative-positive dusty grains have been examined. To study dissipative DIA mode properties, a reductive perturbation (RP) analysis is used under convenient geometrical coordinate transformation, three-dimensional damped Kadomtsev–Petviashvili (3D-CDKP) equation in cylindrical coordinates is obtained. Effects of collisional parameters on damped soliton pulse structures are studied. More specifically, the impact of axial, radial, and polar coordinates with the time on solitary propagation are examined. This investigation may be viable in plasma of the Earth’s mesosphere.

Face-to-Face Collisions of Bright and Dark Ion Acoustic Solitons in Superthermal Electrons for Different Geometrical Configurations

Abstract The face-to-face collision of ion acoustic solitons (IASs) in superthermal plasmas composed of positive and negative ion fluids and superthermal electrons is investigated for different geometrical configurations. For the generic case, the extended Poincaré-Lighthill-Kuo (EPLK) analysis is employed to obtain the extended Korteweg-de Vries (EKdV) equations and phase shift equations. The non-linear propagation and the face-to-face collision of bright and dark IASs are studied. In addition, when the concentration of ion reaches the critical value, the EPLK method is applied to obtain the modified Korteweg-de Vries (mKdV) equations and the phase shift relations, which govern the excitation and the face-to-face collision of bright and dark IASs. Appropriately, the effects of several parameters such as the electron concentration, the superthermality of electrons and the diversity in the system’s geometry under consideration on the trajectories of IASs after the collision are discussed. Numerical calculations lead to some highlights on the properties of bright and dark IASs (e.g. in laboratory plasmas such as laser–matter/plasma interaction experiments and in astrophysical environments such as lower part of magnetosphere).

Bernstein-Greene-Kruskal theory of electron holes in superthermal space plasma

Several spacecraft missions have observed electron holes (EHs) in Earth's and other planetary magnetospheres. These EHs are modeled with the stationary solutions of Vlasov-Poisson equations, obtained by adopting the Bernstein-Greene-Kruskal (BGK) approach. Through the literature survey, we find that the BGK EHs are modelled by using either thermal distribution function or any statistical distribution derived from particular spacecraft observations. However, Maxwell distributions are quite rare in space plasmas; instead, most of these plasmas are superthermal in nature and generally described by kappa distribution. We have developed a one-dimensional BGK model of EHs for space plasma that follows superthermal kappa distribution. The analytical solution of trapped electron distribution function for such plasmas is derived. The trapped particle distribution function in plasma following kappa distribution is found to be steeper and denser as compared to that for Maxwellian distribution. The width-amplitude relation of perturbation for superthermal plasma is derived and allowed regions of stable BGK solutions are obtained. We find that the stable BGK solutions are better supported by superthermal plasmas compared to that of thermal plasmas for small amplitude perturbations.

Effect of externally applied periodic force on ion acoustic waves in superthermal plasmas

Ion acoustic solitary waves in superthermal plasmas are investigated in the presence of trapped electrons. The reductive perturbation technique is employed to obtain a forced Korteweg–de Vries-like Schamel equation. An analytical solution is obtained in the presence of externally applied force. The effect of the external applied periodic force is also observed. The effect of the spectral index (κ), the strength (f0), and the frequency (ω) on the amplitude and width of the solitary wave is obtained. The result may be useful in laboratory plasma as well as space environments.

Analytical Solitary Wave Solution of the Dust Ion Acoustic Waves for the Damped Forced Korteweg–de Vries Equation in Superthermal Plasmas

Abstract Analytical solitary wave solution of the dust ion acoustic (DIA) waves was studied in the framework of the damped forced Korteweg–de Vries (DFKdV) equation in superthermal collisional dusty plasmas. The reductive perturbation technique was applied to derive the DKdV equation. It is observed that both the rarefactive and compressive solitary wave solutions are possible for this plasma model. The effects of κ and the strength (f 0) and frequency (ω) of the external periodic force were studied on the analytical solitary wave solution of the DIA waves. It is observed that the parameters κ, f 0 and ω have significant effects on the structure of the damped forced DIA solitary waves. The results of this study may have relevance in laboratory plasmas as well as in space plasmas.

Analytical electron acoustic solitary wave solution for the forced KdV equation in superthermal plasmas

Analytical electron acoustic solitary wave (EASW) solution is investigated in the presence of periodic force for an unmagnetized plasma consisting of cold electron fluid, superthermal hot electrons, and stationary ions. Employing the reductive perturbation technique, the forced Korteg-de Vries (KdV) equation is derived for electron acoustic waves. For the first time, an analytical solution for EASWs is derived in the presence of periodic force. The effects of the ratio between hot electron and cold electron number densities at equilibrium (α), spectral index (κ), speed of the traveling wave (M), strength (f0), and frequency (ω) of the periodic force are studied on the analytical solution of EASWs. It is observed that the parameters α, κ, M, f0, and ω affect significantly the structures of the electron acoustic solitary waves. The results may have relevance in laboratory plasmas as well as in space plasma environments.

Generation of ion acoustic solitary waves through wave breaking in superthermal plasmas

Space plasmas provide abundant evidence of a highly energetic particle population that results in a long-tailed non-Maxwellian distribution. Such plasmas can be effectively modeled with kappa distribution. The superthermal population in the tail of kappa distribution can have significant effects on the wave dynamical processes. We perform the fluid simulations to examine the effects of superthermal populations on the breaking of the electrostatic ion-acoustic (IA) wave, which is the most fundamental mode, existing in the unmagnetized plasmas. We construct a fluid model for exciting IA waves by employing a kappa distribution function for the superthermal population of electrons along with inertial cold ions (protons). We focused on the nonlinear excitations; in the form of ion acoustic solitary wave (IASW) structures formed through the process of wave breaking, and investigated the role of superthermal electron population in the initiation of the steepening, wave breaking, and propagation characteristics of the IASWs in plasma. From the output of the simulation, we established the criteria for the steepening time based on the variations in the phase velocity of the IASWs. Furthermore, we examined the maximum ponderomotive potential and ponderomotive frequency during the wave breaking process. We found that the time corresponding to the peak in the maximum ponderomotive potential is the time of the initialization of the wave breaking process. We present a detailed investigation of the role of the ponderomotive forces acting on the plasma at each time step, which explains the physics of the wave breaking in nonthermal plasmas.

Solitonic, Periodic and Quasiperiodic Behaviors of Dust Ion Acoustic Waves in Superthermal Plasmas

The solitonic, periodic, and quasiperiodic behaviors of dust ion acoustic waves in superthermal plasmas with q-nonextensive electrons are studied using the bifurcation theory of planar dynamical systems through direct approach. Using a Galilean transformation, model equations are transformed to a Hamiltonian system involving electrostatic potential. The existence of solitary and periodic waves is shown for the unperturbed Hamiltonian system. Analytical forms of these waves are presented depending on physical parameters q and μ. The effects of q and μ are studied on characteristics of nonlinear dust ion acoustic solitary and periodic waves. It is observed that parameters q and μ significantly influence the characteristics of nonlinear dust ion acoustic solitary and periodic structures. Considering an external periodic perturbation, the quasiperiodic behavior of the perturbed Hamiltonian system for dust ion acoustic waves is studied. It is seen that the unperturbed Hamiltonian system has the solitary and periodic wave solutions whereas the perturbed Hamiltonian system has quasiperiodic motion for same values of parameters q,μ and v.