共查询到20条相似文献，搜索用时 440 毫秒
1.
The problems of large amplitude double layers are discussed using Sagdeev’s pseudo-potential technique for a dusty plasma comprising two temperature isothermal ions and nonextensive nonthermal velocity distributed electron. For different sets of plasma parameter values, the Sagdeev potential V(?) has been plotted. It is found that nonextensive q parameter plays a significant role in determining the shape and size of large amplitude double layers. Also, it is observed that the existence of large amplitude double layers depends on different plasma parameters. 相似文献
2.
Electrostatic double layers have been proposed as an acceleration mechanism in solar flares and other astrophysical objects. They have been extensively studied in the laboratory and by means of computer simulations. The theory of steady-state double layers implies several existence criteria, in particular the Bohm criteria, restricting the conditions under which double layers may form. In the present paper several already published theoretical models of different types of double layers are discussed. It is shown that the existence conditions often imply current-driven instabilities in the ambient plasma, at least for strong double layers, and it is argued that such conditions must be used with care when applied to real plasmas. Laboratory double layers, and by implication those arising in astrophysical plasmas often produce instabilities in the surrounding plasma and are generally time-dependent structures. Naturally occuring double layers should, therefore, be far more common than the restrictions deduced from idealised time-independent models would imply. In particular it is necessary to understand more fully the time-dependent behaviour of double layers. In the present paper the dynamics of weak double layers is discussed. Also a model for a moving strong double layer, where an associated potential minimum plays a significant role, is presented.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988. 相似文献
3.
Coherent structures entailing the existence of double layers have been studied in magnetised plasma contaminated with dust
charging fluctuations. It has been shown that the dust charging in magnetic plasma leads to complexity in the derivation of
the Sagdeev wave equation, but under way new procedure enable one to study the nature of double layers showing the effective
role of the constituents of the plasma. A parametric analysis is a subject of interest in laboratory and space plasmas, and
it has been explained with the input of various typical plasma numerics. The proposed mathematical mechanism has shown the
success to yield plasma acoustic modes in a dusty plasma which, in turn, has been solved convincingly for double layers. Observations
have been evaluated in an appropriate model with a view to agree with the observations in astrophysical problems dealing with
present new findings. 相似文献
4.
The nonlinear wave structure of arbitrary amplitude ion acoustic solitary waves (IASWs) are studied in the Sagdeev’s pseudopotential framework for an ultra-relativistic degenerate dense plasma comprising cold and hot electrons and inertial ultra-cold ions. By employing standard normal-mode analysis the dispersion relation for linear waves is studied. The numerical results are presented to understand the features of ion acoustic solitary wave structures. It is shown that the present plasma model supports IASWs having positive potential well. Also, it is found that the small amplitude rarefactive double layer solution can exist in such a plasma system in some parametric region. It is shown that solitary structures and double layers are affected by relevant plasma parameters. 相似文献
5.
H. Alfvén 《Astrophysics and Space Science》1978,54(2):279-292
The methodology of cosmic plasma physics is discussed. It is very hazardous to try to describe plasma phenomena by theories which have not been carefully tested experimentally. One present approach is to rely on laboratory measurements andin situ measurements in the magnetosphere and heliosphere, and to approach galactic phenomena by scaling up the wellknown phenomena to galactic dimensions. A summary is given of laboratory investigations of electric double layers, a phenomenon which is known to be very important in laboratory discharges. A summary is also given of thein situ measurements in the magnetosphere by which the importance of electric double layers in the Earth's surrounding is established. The scaling laws between laboratory and magnetospheric double layers are studied. The successful scaling between laboratory and magnetospheric phenomena encourages an extrapolation to heliospheric phenomena. A further extrapolation to galactic phenomena leads to a theory of double radio sources.In analogy with the Sun which, acting as a homopolar inductor, energizes the heliospheric current system, a rotating magnetized galaxy should produce a similar current system. From analogy with laboratory and magnetospheric current systems it is argued that the galactic current might produce double layers where a large energy dissipation takes place. This leads to a theory of the double radio sources which, within the necessary wide limits of uncertainty, is quantitatively reconcilable with observations. 相似文献
6.
Small amplitude dust-acoustic solitary waves in an unmagnetized dusty plasma consisting of electrons and two temperature ions obeying the q-nonextensive distribution are investigated. Employing reductive perturbation method, the Korteweg-de Vries (KdV) equation is derived. From the solitonic solutions of KdV equation, the influence of nonextensivity of electrons as well as ions and dust concentration on the amplitude and width of dust-acoustic solitary waves has been studied. It is observed that both positive and negative potential dust acoustic solitary waves occur in this case. The modified KdV (mKdV) equation is derived in order to examine the solitonic solutions for the critical plasma parameters for which KdV theory fails. The parametric regimes for the existence of mKdV solitons and double layers (DLs) have also been determined. Positive potential double layers are found to occur in the present study. 相似文献
7.
Ion–acoustic double layers has been studied in magnetized electron-positron-ion plasma. The modified Korteweg-de Vries (m-KdV) is derived using reductive perturbation method. It is found that for the selected set of parameters, the system supports rarefactive (compressive) double layers depending upon the values of cold electron concentration (μ). It is also found that the magnetization affects only the width of the double layer. For a given set of parameter values, as we increases the magnetization, the width of the double layer increases and an increases in the obliqueness θ, where θ is the angle between wave vector and magnetic field, the width of the double layer also increases. The angle of obliqueness θ does not affects the amplitude of the double layer. It is also investigated that for the given set of parameter values, on increasing the positron concentration the amplitude of the rarefactive (compressive) double layer decreases (increases), and the width of the rarefactive (compressive) double layer increases (decreases). The effect of the temperature ratios of ions and positron on the amplitude and width of the double layers are discussed. 相似文献
8.
The propagation of ion-acoustic waves by the augmentation of Kadomtsev-Petviashvili equation are studied in a plasma in relation to that existing in the interplanetary space. We precisely pointed out the causes of occuring the double layers as well as collapsing of the solitary waves in the plasma dynamics. 相似文献
9.
Uday Narayan Ghosh Deb Kumar Ghosh Prasanta Chatterjee Biswajit Sahu 《Astrophysics and Space Science》2012,342(2):449-456
The basic features of planar and nonplanar time-dependent dust-ion-acoustic (DIA) solitary waves (SWs) and double layers (DLs) have been studied in an unmagnetized dusty plasma system consisting of positively and negatively charged dust, Boltzmann distributed ions and superthermal electrons (represented by kappa distribution). Using the reductive perturbation technique (RPT) we have derived modified Gardner (MG) equation, which gives information beyond the Korteweg-de Vries (KdV) limits (corresponding to the vanishing of nonlinear coefficient of the KdV equation). It is seen that the properties of nonplanar DIA SWs and DLs are significantly differs as the value of spectral index kappa (κ) changes. The present investigation may have relevance in the study of propagation of DIA waves in space and laboratory plasmas. 相似文献
10.
P. Carlqvist 《Astrophysics and Space Science》1982,87(1-2):21-39
A model of a strong, time-independent, and relativistic double layer is studied. Besides double layers having the electric field parallel to the current the model also describes a certain type of oblique double layers. The Langmuir condition (ratio of ion current density to electron current density) as well as an expression for the potential drop of the double layer are derived. Furthermore, the distributions of charged particles, electric field, and potential within the double layer are clarified and discussed. It is found that the properties of relativistic double layers differ substantially from the properties of corresponding non-relativistic double layers. 相似文献
11.
An evacuation process due to the growth of current driven instabilties in a plasma is discussed. The process, which leads to localized extreme density reductions, is related to the formation of electrostatic double layers. The initial linear phase is treated using the superposition of unstable plasma waves. In the long wavelength, non-dispersive limit, a density dip — which is initially present as a small disturbance — grows rapidly and remains localized in the plasma. The process works for a variety of plasma conditions provided a certain current density is exceeded. For a particular choice of plasma parameters the non-linear development is followed, by solving the coupled Vlasov-Poisson equations by finite difference methods. The evacuation process is found to work even more effectively in the non-linear phase and leads to an extreme density reduction within the dip. It is suggested that the growth of such structures produces weak points within the plasma that can lead to the formation of double layers. 相似文献
12.
Linear and nonlinear studies are presented for an electron-ion plasma system which is being energized with an external beam of positrons. The electrons are assumed to follow the q-nonextensive velocity distribution. The growth rates of instability due to positron beam are analyzed numerically. The compressive and rarefactive double layers are studied in the system and it is found that by varying the entropic index parameter q, positron beam speed v po and concentration of positrons p, the dynamics of nonlinear profile is changing quite effectively. The relevance of the work regarding to astrophysical space plasma is pointed out. 相似文献
13.
Sanjay Sarkar 《Astrophysics and Space Science》2014,349(1):245-253
Dust-ion-acoustic (DIA) waves in an unmagnetized dusty plasma system consisting of inertial ions, negatively charged immobile dust, and superthermal (kappa distributed) electrons with two distinct temperatures are investigated both numerically and analytically by deriving Korteweg–de Vries (K-dV), modified K-dV (mK-dV), and Gardner equations along with its double layers (DLs) solutions using the reductive perturbation technique. The basic features of the DIA Gardner solitons (GSs) as well as DLs are studied, and an analytical comparison among K-dV, mK-dV, and GSs are also observed. The parametric regimes for the existence of both the positive as well as negative SWs and negative DLs are obtained. It is observed that superthermal electrons with two distinct temperatures significantly affect on the basic properties of the DIA solitary waves and DLs; and depending on the parameter μ c (the critical value of relative electron number density μ e1), the DIA K-dV and Gardner solitons exhibit both compressive and rarefactive structures, whereas the mK-dV solitons support only compressive structures and DLs support only the rarefactive structures. The present investigation can be very effective for understanding and studying various astrophysical plasma environments (viz. Saturn magnetosphere, pulsar magnetosphere, etc.). 相似文献
14.
Properties of propagation of large amplitude dust ion-acoustic solitary waves and double layers are investigated in electron-positron-ion plasma with highly charged negative dust. Sagdeev pseudopotential method has been used to derive the energy balance equation. The expression for the critical Mach number (lower/upper limit) for the existence of solitary structures has also been derived. The Sagdeev pseudopotential is a function of numbers of physical parameters such as ion temperature (σ), positron density (δ p ), dust density (δ d ) and electron to positron temperature ratio (β). These parameters significantly influence the properties of the solitary structures and double layers. Further it is found that both polarity (compressive and rarefactive) solitons and negative potential double layers are observed. 相似文献
15.
Distributions of plasma with excess numbers of superthermal electrons are common in space environments and double layer (DL)
is one of the very important electrostatic nonlinear wave structures ubiquitous in plasma systems. Based on the modified Zakharov
equations, the DLs are studied in the strong turbulent plasmas with Kappa distributed electrons. It appears that in the strong
turbulence regime, the presence of additional superthermal particles does not make qualitative changes on the DLs behavior,
but modify the thicknesses of the DLs. 相似文献
16.
Electrostatic solitary waves and double layers (DLs) formed by the coupled ion acoustic (IA) and drift waves have been investigated in non-uniform plasma using \(q\)-nonextensive distribution function for the electrons and assuming ions to be cold \(T_{i}< T_{e}\). It is found that both compressive and rarefactive nonlinear structures (solitary waves and DLs) are possible in such a system. The steeper gradients are supportive for compressive solitary (and double layers) and destructive for rarefactive ones. The \(q\)-nonextensivity parameter \(q\) and the magnitudes of gradient scale lengths of density and temperature have significant effects on the amplitude of the double layers (and double layers) as well as on the speed of these structures. This theoretical model is general which has been applied here to the \(F\)-region ionosphere for illustration. 相似文献
17.
R. Bharuthram 《Astrophysics and Space Science》1992,189(2):213-222
The existence and properties of arbitrary amplitude double layers in a four-component electron-positron plasma, consisting of two species of hot electrons, a hot and a cold positron species, are investigated as functions of plasma properties such as density and temperature ratios. Their behaviour for other plasma models is also discussed. Applications to the polar-cusp region of pulsars is considered. 相似文献
18.
Yasunori Nejoh 《Astrophysics and Space Science》1996,235(2):245-253
The stationary ion-acoustic double layer is investigated in a plasma with an electron beam. The condition of the existence sensitively depends on the parameters such as the electron beam temperature, the ion temperature, the beam density and the effect of the trapped electrons. The properties of the double layer are also depicted. It turns out that the electron beam velocity is relatively small. This investigation predicts new findings of the ion-acoustic double layers in a plasma with an electron beam. 相似文献
19.
A theoretical investigation has been made on the Dust ion-acoustic (DIA) Gardner solitons (GSs) and double layers (DLs) in electronegative plasma consisting of inertial positive and negative ions, super-thermal (kappa distributed) electrons, and negatively charged static dust. The standard reductive perturbation method is employed to derive the Korteweg-de Vries (K-dV), modified K-dV (mK-dV), and standard Gardner equations, which admits solitary waves (SWs) and DLs solutions. It have been found that GSs and DLs exist for α around its critical value α c , where α c is the value of α corresponding to the vanishing of the nonlinear coefficient of the K-dV equation. The parametric regimes for the existence of both the positive as well as negative SWs and negative DLs are obtained. The basic features of DIA SWs and DLs are analyzed and it has been found that the polarity, speed, height, thickness of such DIA SWs and DLs structures, are significantly modified due to the presence of two types of ions and spectral index (κ) of super-thermal electrons. It has also been found that the characteristics of DIA GSs and DLs, are different from that of the K-dV solitons and mK-dV solitons. The relevance of our results to different interstellar space plasma situations are discussed. 相似文献
20.
A one-dimensional, self consistent theoretical model is constructed for double layers in a thermodynamically nonequilibrium
astrophysical plasma. A steady state is maintained by an asymmetry in the fluxes from both sides. The range of possible values
of the parameters is determined. 相似文献