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1.
Properties of fully nonlinear electron-acoustic solitary waves in an unmagnetized and collisionless electron-positron-ion plasma containing cold dynamical electrons, superthermal electrons and positrons obeying Cairns’ distribution have been analyzed in the stationary background of massive positive ions. A linear dispersion relation has been derived, from which it is found that even in the absence of superthermal electrons, the superthermal positron component can provide the restoring force to the cold inertial electrons to excite electron-acoustic waves. Moreover, superthermal electron and positron populations seem to enhance the electron acoustic wave phase speed. For nonlinear analysis, Korteweg-de Vries equation is obtained using the reductive perturbation technique. It is found that in the presence of positron both hump and dip type solitons appear to excite. The present work may be employed to explore and to understand the formation of electron acoustic soliton structures in the space and laboratory plasmas with nonthermal electrons and positrons. 相似文献
2.
S. K. El-Labany R. Sabry W. M. Moslem E. A. Elghmaz 《Astrophysics and Space Science》2014,349(2):773-780
Generation of quasielastic electron-acoustic (EA) waves head-on collision are investigated in non-planar (cylindrical/spherical) plasma composed of cold electrons fluid, hot electrons obeying nonthermal distribution, and stationary ions. The cylindrical/spherical Korteweg-de Vries (KdV) equations describing two bidirectional EA waves are derived and solved analytically. Numerical investigation have shown that only positive electron-acoustic (EA) structures can propagate and collide. The analytical phase shift |Δ A | due to the non-Maxwellian (nonthermal) electrons is different from the Maxwellian case. Both the hot-to-cold electron number density ratio α and nonthermal parameter β have opposite effect on the phase shift behavior. The phase shift of the spherical EA waves is smaller than the cylindrical case, which indicates that the former is more stable for collision. The relevance of the present study to EA waves propagating in the Earth’s auroral zone is highlighted. 相似文献
3.
S. K. El-Labany M. Shalaby R. Sabry L. S. El-Sherif 《Astrophysics and Space Science》2012,340(1):101-108
A theoretical investigation is carried out for understanding the properties of electron-acoustic potential structures (i.e.,
solitary waves and double-layers) in a magnetized plasma whose constituents are a cold magnetized electron fluid, hot electrons
obeying a nonthermal distribution, and stationary ions. For this purpose, the hydrodynamic equations for the cold magnetized
electron fluid, nonthermal electron density distribution, and the Poisson equation are used to derive the corresponding nonlinear
evolution equation; modified Zakharov–Kuznetsov (MZK) equation, in the small amplitude regime. The MZK equation is analyzed
to examine the existence regions of the solitary pulses and double-layers. It is found that rarefactive electron-acoustic
solitary waves and double-layers strongly depend on the density and temperature ratios of the hot-to-cold electron species
as well as the nonthermal electron parameter. 相似文献
4.
S. K. El-Labany W. F. El-Taibany M. M. El-Fayoumy 《Astrophysics and Space Science》2012,341(2):527-534
Propagation regimes of large-amplitude dust-ion acoustic solitary wave in a dusty plasma with nonthermal electrons are analyzed by employing the Sagdeev potential technique. Two domains of the Mach numbers are defined depending on the nonthermal and plasma parameters. The two types of soliton solution are found to be exited corresponding to certain values of the nonthermal parameter. Numerical solutions are presented that illustrate the dependence of soliton characteristics on practically interesting plasma and nonthermal parameters. The findings of this investigation could be useful in understanding the detected solitary waves in space plasma in the presence of nonthermal electrons such as electrostatic solitary structures observed in Saturn’s E-ring. 相似文献
5.
The problem of arbitrary amplitude electron-acoustic solitary (EAS) waves in a plasma having cold fluid electrons, hot superthermal electrons and stationary ions is addressed. The domain of their allowable Mach numbers enlarges as the spectral index κ increases revealing therefore that the “maxwellisation” process of the hot component favors the propagation of the EAS waves. As the superthermal character of the plasma is increased, the potential pulse amplitude increases while its width is narrowed, i.e, the superthermal effects makes the electron-acoustic solitary structure more spiky. As the spectral index κ decreases, the hot electrons are locally expelled and pushed out of the region of the soliton’s localization. A decrease of the fractional number density of the hot electrons relative to that of the cold ones number density would lead to an increase of the depth as well as the width of the localized EAS wave. Our results should help to understand the salient features of large amplitude localized structures that may occur in the plasma sheet boundary layer and may provide an explanation for the strong spiky waveforms that have been observed in auroral electric fields. 相似文献
6.
Properties of fully nonlinear ion-acoustic solitary waves in an unmagnetized and collisionless pair-ion (PI) plasma containing superthermal electrons obeying Cairns distribution have been analyzed. A linear biquadratic dispersion relation has been derived, which yields the fast (supersonic) and slow (subsonic) modes in a pair-ion-electron plasma with nonthermal electrons. For nonlinear analysis, Korteweg-de Vries equation is obtained using the reductive perturbation technique. It is found that in case of slow mode, both electrostatic hump and dip type structures are formed depending on the temperature difference between positively and negatively charged ions, whereas, only dip type solitary structures have been observed for fast mode. The present work may be employed to explore and to understand the formation of solitary structures in the space (especially, the Earth’s ionosphere where two distinct pair ion species (H ±) are present) and laboratory produced pair-ion plasmas with nonthermal electrons. 相似文献
7.
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. 相似文献
8.
Electron-acoustic solitary structures in two-electron-temperature plasma with superthermal electrons
The propagation of nonlinear electron-acoustic waves (EAWs) in an unmagnetized collisionless plasma system consisting of a
cold electron fluid, superthermal hot electrons and stationary ions is investigated. A reductive perturbation method is employed
to obtain a modified Korteweg–de Vries (mKdV) equation for the first-order potential. The small amplitude electron-acoustic
solitary wave, e.g., soliton and double layer (DL) solutions are presented, and the effects of superthermal electrons on the
nature of the solitons are also discussed. But the results shows that the weak stationary EA DLs cannot be supported by the
present model. 相似文献
9.
The purpose of this paper is to investigate the crossing point of the power-law distribution lines calculated during different times of microwave and hard X-ray bursts. A linear correlation between the logarithm of the total density and the energy index of nonthermal electrons described by a power-law is proven to be a necessary condition for the crossing of a group of power-law distribution lines corresponding to the time evolution of the nonthermal electrons during a solar microwave and HXR burst. The common crossing point of these lines may be considered as evidence of a common cutoff energy of the nonthermal electrons responsible for gyrosynchrotron or bremsstrahlung radiation. When the common crossing point is close to the low-energy cutoff, the correlation coefficient is negative, and vice versa. The result may be useful for estimating the cutoff energy as well as the particle acceleration mechanism. 相似文献
10.
Propagation of cylindrical and spherical electron-acoustic solitary waves in unmagnetized plasmas consisting of cold electron
fluid, hot electrons obeying a superthermal distribution and stationary ions are investigated. The standard reductive perturbation
method is employed to derive the cylindrical/spherical Korteweg-de-Vries equation which governs the dynamics of electron-acoustic
solitons. The effects of nonplanar geometry and superthermal hot electrons on the behavior of cylindrical and spherical electron
acoustic soliton and its structure are also studied using numerical simulations. 相似文献
11.
Anirban Guha Barin Kumar De Abhijit Choudhury Rakesh Roy 《Astrophysics and Space Science》2012,338(2):287-294
The problem of solitary electron acoustic (EA) wave propagation in a plasma with nonthermal hot electrons featuring the Tsallis
distribution is addressed. A physically meaningful nonextensive nonthermal velocity distribution is outlined. It is shown
that the effect of the nonthermal electron nonextensivity on EA waves can be quite important. Interestingly, we found that
the phase speed of the linear EA mode increases as the entropic index q decreases. This enhancement is weak for q>1, and significant for q<1. For a given nonthermal state, the minimum value of the allowable Mach numbers is lowered as the nonextensive nature of
the electrons becomes important. This critical limit is shifted towards higher values as the nonthermal character of the plasma
is increased. Moreover, our plasma model supports rarefactive EA solitary waves the main quantities of which depend sensitively
on q. This dependency (for q>1) becomes less noticeable as the nonthermal parameter decreases. Nevertheless, decreasing α yields for q<0 a different result, a trend which may be attributed to the functional form of the nonthermal nonextensive distribution.
Our study (which is not aimed at putting the ad hoc Cairns distribution onto a more rigorous foundation) suggests that a background
electron nonextensivity may influence the EA solitons. 相似文献
12.
Using the standard reductive perturbation technique, nonlinear cylindrical and spherical Kadomtsev-Petviashvili (KP) equations are derived for the propagation of ion acoustic solitary waves in an unmagnetized collisionless plasma with nonthermal electrons and warm ions. The influence of nonthermally distributed electrons and the effects caused by the transverse perturbation on cylindrical and spherical ion acoustic waves (IAWs) are investigated. It is observed that the presence of nonthermally distributed electrons has a significant role in the nature of ion acoustic waves. In particular, when the nonthermal distribution parameter ?? takes certain values the usual cylindrical KP equation (CKPE) and spherical KP equation (SKPE) become invalid. One then has to have recourse to the modified CKPE or SKPE. Analytical solutions of both CKPE and SKPE and their modified versions are discussed in the present paper. The present investigation may have relevance in the study of propagation of IAWs in space and laboratory plasmas. 相似文献
13.
Electron-acoustic waves are studied with orbital angular momentum (OAM) in an unmagnetized collisionless uniform plasma, whose constituents are the Boltzmann hot electrons, inertial cold electrons and stationary ions. For this purpose, we employ the fluid equations to obtain a paraxial equation in terms of cold electron density perturbations, which admits both the Gaussian and Laguerre–Gaussian (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is found, which also allows us to express the components of the electric field in terms of LG potential perturbations. Calculating the energy flux of the electron-acoustic waves, an OAM density for these waves is obtained. Numerically, it is found that the parameters, such as, azimuthal angle, radial and angular mode numbers, and the beam waist strongly modify the LG potential profiles associated with electron-acoustic waves. The present results should be helpful to study the trapping and transportation of plasma particles and energy as well as to understand the electron-acoustic mode excitations produced by the Raman backscattering of laser beams in a uniform plasma. 相似文献
14.
This work demonstrates the possibility of magnetic-field topology investigations using microwave polarimetric observations. We study a solar flare of GOES M1.7 class that occurred on 11 February, 2014. This flare revealed a clear signature of spatial inversion of the radio-emission polarization sign. We show that the observed polarization pattern can be explained by nonthermal gyrosynchrotron emission from the twisted magnetic structure. Using observations of the Reuven Ramaty High Energy Solar Spectroscopic Imager, Nobeyama Radio Observatory, Radio Solar Telescope Network, and Solar Dynamics Observatory, we have determined the parameters of nonthermal electrons and thermal plasma and identified the magnetic structure where the flare energy release occurred. To reconstruct the coronal magnetic field, we use nonlinear force-free field (NLFFF) and potential magnetic-field approaches. Radio emission of nonthermal electrons is simulated by the GX Simulator code using the extrapolated magnetic field and the parameters of nonthermal electrons and thermal plasma inferred from the observations; the model radio maps and spectra are compared with observations. We have found that the potential-magnetic-field approach fails to explain the observed circular polarization pattern; on the other hand, the Stokes-\(V\) map is successfully explained by assuming nonthermal electrons to be distributed along the twisted magnetic structure determined by the NLFFF extrapolation approach. Thus, we show that the radio-polarization maps can be used for diagnosing the topology of the flare magnetic structures where nonthermal electrons are injected. 相似文献
15.
A theoretical investigation is made on the formation as well as basic properties of dust-ion-acoustic (DIA) shock waves in a magnetized nonthermal dusty plasma consisting of immobile charge fluctuating dust, inertial ion fluid and nonthermal electrons. The reductive perturbation method is employed to derive the Korteweg-de Vries-Burgers equation governing the DIA shock waves. The combined effects of external static magnetic field, obliqueness, nonthermal electron distribution and dust charge fluctuation on the DIA shock waves are also investigated. It is shown that the dust charge fluctuation is a source of dissipation, and is responsible for the formation of the DIA shock waves. It is also observed that the combined effects of obliqueness, nonthermal electron distribution and dust charge fluctuation significantly modify the basic properties of the DIA shock waves. The implications of our results in space and laboratory dusty plasma situations are briefly discussed. 相似文献
16.
Propagation of ion acoustic solitary waves are studied in e-p-i plasmas containing high relativistic ions, Maxwell–Boltzmann
distributed positrons and nonthermal electrons. Reductive perturbation method is used and the Korteweg-de Vries (KdV) equation
is derived. The effects of high relativistic ions and nonthermal electrons on soliton characters are studied. 相似文献
17.
《Chinese Astronomy and Astrophysics》1987,11(1):20-24
We propose to interpret the nonthermal emission lines of molecular clouds by a Cerenkov radio line emission mechanism. Relativistic electrons passing through a cloud with population inversion can generate microwave emission lines of anomalous intensity ratios. Calculations for nonthermal emission lines of OH sources of Group I Ia associated with supernova remnants show that this nonthermal mechanism may provide a hopeful way of solving certain difficulties of the theory of celestial masers. 相似文献
18.
A rigorous theoretical investigation has been made on the obliquely propagating dust-acoustic (DA) waves in a magnetized dusty plasmas consisting of distinct temperature q-distributed electrons with distinct strength of nonextensivities, nonthermal ions and negatively charged mobile dust grains, and analyzed by deriving the Zakharov-Kuznetsov equation. It is found that the characteristics and the properties of the DA solitary waves (DASWs) are significantly modified by the external magnetic field, relative temperature ratio of ions, relative number densities of electrons as well as ions, the nonextensivity of electrons, nonthermality of ions and the obliqueness of the system. The possible implications of the results obtained from this analysis in space and laboratory dusty plasmas are briefly addressed. 相似文献
19.
Parvin Eslami Marzieh Mottaghizadeh Hamid Reza Pakzad 《Astrophysics and Space Science》2012,338(2):271-278
The head-on collision between two electron-acoustic solitary waves (EASWs) in an unmagnetized plasma is investigated, including
a cold electrons fluid, hot electrons, obeying a nonextensive distribution and stationary ions. By using the extended Poincaré-Lighthill–Kuo
(PLK) perturbation method, the analytical phase shifts following the head-on collision are derived. The effects of the ratio
of the number density of hot electrons to the number density of cold electrons α, and the nonextensive parameter q on the phase shifts are studied. It is found that q and the hot-to-cold electron density ratio significantly modify the phase shifts. 相似文献
20.
S. K. El-Labany R. Sabry W. F. El-Taibany E. A. Elghmaz 《Astrophysics and Space Science》2012,340(1):77-85
The nonlinear ion-acoustic double layers (IADLs) in a warm magnetoplasma with positive-negative ions and nonthermal electrons
are investigated. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density
distribution, and the Poisson equation are used to derive a modified Zakharov–Kuznetsov (MZK) equation, in the small amplitude
regime. It is found that compressive and rarefactive IADLs strongly depend on the mass and density ratios of the negative-to-positive
ions as well as the nonthermal electron parameter. Also, it is shown that there are one critical value for the density ratio
of the negative-to-positive ions (ν), the ratio between unperturbed electron-to-positive ion density (μ), and the nonthermal electron parameter (β), which decide the existence of positive and negative IADLs. The present study is applied to examine the small amplitude
nonlinear IADL excitations for the (H+, O2-)(\mathrm{H}^{+}, \mathrm{O}_{2}^{-}) and (H+,H−) plasmas, where they are found in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in
understanding the salient features of the nonlinear IADLs in either space or laboratory plasmas where two distinct groups
of ions and non-Boltzmann distributed electrons are present. 相似文献