共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
M. Rosenberg 《Astrophysics and Space Science》2001,277(1-2):125-133
Ionized gases containing fine (μm to sub-μm sized) charged dust grains, referred to as dusty plasmas, occur in diverse cosmic
and laboratory environments. Dust occurs in many space and astrophysical environments, including planetary rings, comets,
the Earth's ionosphere, and interstellar molecular clouds. Dust also occurs in laboratory plasmas, including processing plasmas,
and crystallized dusty plasmas. Charged dust can lead to various effects in a plasma. In this review, some physical processes
in dusty plasmas are discussed, with an emphasis on applications to dusty plasmas in space. This includes theoretical work
on several wave instabilities, the role of dust as an electron source, and Coulomb crystals of positively charged dust.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
The nonlinear coupling between a large amplitude electromagnetic wave and the slow background motion in a dusty plasma is considered. Stimulated scattering instabilities are investigated. The relevance of our investigation to cometary and astrophysical plasmas is pointed out. 相似文献
4.
Theoretical investigation is carried out to understand the dynamics and stability of three dimensional ion solitary waves propagating in dense plasma comprising of ultra-relativistic degenerate electrons and positrons and warm ions. A linear dispersion relation is derived which shows a strong dependence of wave on positron concentration (through the change of density balance) and ion-to-degenerate electron temperature ratio. A nonlinear Kadomtsev-Petviashvili equation is derived by employing the reductive perturbation technique and solved analytically and the conditions for existence of stable solitary waves are found. The analysis reveals that only compressive solitary waves exist in the system. Effects of the change of density balance and Fermi temperature ratios are studied in detail, both analytically and numerically. Furthermore, the conditions for stable solitary waves are discussed by using energy consideration method. The numerical results are also presented by using the parameters consistent with the degenerate and ultrarelativistic astrophysical plasmas. 相似文献
5.
Electromagnetic instabilities in high-β plasmas, where β is the ratio of the kinetic plasma energy to the magnetic energy, have a broad range of astrophysical applications. The presence
of temperature anisotropies T
∥
/T
⊥
>1 (where ∥ and ⊥ denote directions relative to the background magnetic field) in solar flares and the solar wind is sustained by the observations
and robust acceleration mechanisms that heat plasma particles in the parallel direction. The surplus of parallel kinetic energy
can excite either the Weibel-like instability (WI) of the ordinary mode perpendicular to the magnetic field or the firehose
instability (FHI) of the circularly polarized waves at parallel propagation. The interplay of these two instabilities is examined.
The growth rates and the thresholds provided by the kinetic Vlasov – Maxwell theory are compared. The WI is the fastest growing
one with a growth rate that is several orders of magnitude larger than that of the FHI. These instabilities are however inhibited
by the ambient magnetic field by introducing a temperature anisotropy threshold. The WI admits a larger anisotropy threshold,
so that, under this threshold, the FHI remains the principal mechanism of relaxation. The criteria provided here by describing
the interplay of the WI and FHI are relevant for the existence of these two instabilities in any space plasma system characterized
by an excess of parallel kinetic energy. 相似文献
6.
A.R. Bell 《Astrophysics and Space Science》1997,256(1-2):13-35
This paper reviews the use of computational simulation in plasma physics. It describes a range of numerical models varying from particle models of low density collisionless plasmas to fluid models of high density collision-dominated plasmas. Some applications of these models, particularly to laser-produced and astrophysical plasmas, are described. 相似文献
7.
F. Mottez 《Astrophysics and Space Science》2001,277(1-2):59-70
This tutorial paper is devoted to theoretical aspects of the coherent electrostatic structures that have been encountered
in various space plasmas. These structures, called solitary waves, electrostatic shocks or double layers have been observed
in the solar wind, the Earth bow shock, the auroral zones and the magnetotail. Most of these structures can be interpreted
in terms of electron or ion phase space holes. Their1D structure, their emergence from plasma instabilities, their mutual
interactions, their bidimensional stability, and their ability to create large scale electric fields are discussed in this
paper.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Anthony L. Peratt 《Astrophysics and Space Science》1997,256(1-2):51-75
Advances in the simulation of astrophysical and cosmic plasmas are the direct result of advances in computational capabilities, today consisting of new techniques such as multilevel concurrent simulation, multi-teraflop computational platforms and experimental facilities for producing and diagnosing plasmas under extreme conditions for the benchmarking of simulations. Examples of these are the treatment of mesoscalic plasma and the scaling to astrophysical and cosmic dimensions and the Accelerated Strategic Computing Initiative whose goal is to construct petaflop (1015 floating operations per second) computers, and pulsed power and laser inertial confinement plasmas where megajoules of energy are delivered to highly-diagnosed plasmas. This paper concentrates on the achievements to date in simulating and experimentally producing plasmas scaled to both astrophysical and cosmic plasma dimensions. A previous paper (Part I, Peratt, 1997) outlines the algorithms and computational growth. 相似文献
9.
The non-thermal shielding effects on the inverse Compton scattering are investigated in astrophysical non-thermal Lorentzian plasmas. The inverse Compton power is obtained by the modified Compton scattering cross section in Lorentzian plasmas with the blackbody photon distribution. The total Compton power is also obtained by the Lorentzan distribution of plasmas. It is found that the influence of non-thermal character of the plasma suppresses the inverse Compton power in astrophysical Lorentzian plasmas. It is also found that the non-thermal effect on the inverse Compton power decreases with an increase of the temperature. In addition, the non-thermal effect on the total Compton power with Lorentzan plasmas increases in low-temperature photons and, however, decreases in intermediate-temperature photons with increasing Debye length. The variation of the total Compton power is also discussed. 相似文献
10.
Estelle Asseo Alain Riazuelo 《Monthly notices of the Royal Astronomical Society》2000,318(4):983-1004
The properties of waves able to propagate in a relativistic pair plasma are at the basis of the interpretation of several astrophysical observations. For instance, they are invoked in relation to radio emission processes in pulsar magnetospheres and to radiation mechanisms for relativistic radio jets. In such physical environments, pair plasma particles probably have relativistic, or even ultrarelativistic, temperatures. Besides, the presence of an extremely strong magnetic field in the emission region constrains the particles to one-dimensional motion: all the charged particles strictly move along magnetic field lines.
We take anisotropic effects and relativistic effects into account by choosing one-dimensional relativistic Jűttner–Synge distribution functions to characterize the distribution of electrons and/or positrons in a relativistic, anisotropic pair plasma. The dielectric tensor, from which the dispersion relation associated with plane wave perturbations of such a pair plasma is derived, involves specific coefficients that depend on the distribution function of particles. A precise determination of these coefficients, using the relativistic one-dimensional Jűttner–Synge distribution function, allows us to obtain the appropriate dispersion relation. The properties of waves able to propagate in anisotropic relativistic pair plasmas are deduced from this dispersion relation. The conditions in which a beam and a plasma, both ultrarelativistic, may interact and trigger off a two-stream instability are obtained from this same dispersion relation. Two astrophysical applications are discussed. 相似文献
We take anisotropic effects and relativistic effects into account by choosing one-dimensional relativistic Jűttner–Synge distribution functions to characterize the distribution of electrons and/or positrons in a relativistic, anisotropic pair plasma. The dielectric tensor, from which the dispersion relation associated with plane wave perturbations of such a pair plasma is derived, involves specific coefficients that depend on the distribution function of particles. A precise determination of these coefficients, using the relativistic one-dimensional Jűttner–Synge distribution function, allows us to obtain the appropriate dispersion relation. The properties of waves able to propagate in anisotropic relativistic pair plasmas are deduced from this dispersion relation. The conditions in which a beam and a plasma, both ultrarelativistic, may interact and trigger off a two-stream instability are obtained from this same dispersion relation. Two astrophysical applications are discussed. 相似文献
11.
In many astrophysical problems, the study of the stability of an atmosphere in the presence of a magnetic field is of importance. In most cases the MHD instabilities of atmospheres are studied by energy principle of Bernsteinet al. (1958). In this paper, a general method for studying the stability of a system subject to MHD equations of conditions has been proposed. This is based on the local potential concept put forward by Glansdorff and Prigogine (1964). The scheme for securing stability criteria has been demonstrated in two particular cases. 相似文献
12.
The high-energy processes which occur in many astrophysical objects have motivated recent studies (e.g., Tsintsadze and Tsikarishvili, 1976; Ferrariet al., 1978; Sweeney and Stewart, 1978) of large amplitude wave propagation in plasmas. Such investigations are also of interest for laboratory experiments where strong laser radiation interacts with a high-density target. In the present paper we shall show that even rather small amplitude waves in the presence of an external magnetic field can induce particle velocities which are comparable to the velocity of light. In this ultrarelativistic limit we shall demonstrate that two completely new types of circularly polarized waves appear and that under certain conditions, modulational instabilities occur. Finally we look at the possibility to relate the amplitudes and wavelengths of such waves to pulsar data. 相似文献
13.
The coherent plasma process such as parametric decay instability (PDI) has been applied to a homogeneous and unmagnetized
plasma. These instabilities cause anomalous absorption of strong electromagnetic radiation under specific conditions of energy
and momentum conservation and thus cause anomalous heating of the plasma. The maximum plasma temperatures reached are functions
of luminosity of the radio radiation and plasma parameters. We believe that these processes may be taking place in many astrophysical
objects. Here, the conditions in the sources 3C 273, 3C 48 and Crab Nebula are shown to be conducive to the excitation of
PDI. These processes also contribute towards the absorption of 21cm radiation 相似文献
14.
Anthony L. Peratt 《Astrophysics and Space Science》1996,242(1-2):93-163
Plasma science is rich in distinguishable scales ranging from the atomic to the galactic to the meta-galactic, i.e., themesoscale. Thus plasma science has an important contribution to make in understanding the connection between microscopic and macroscopic phenomena. Plasma is a system composed of a large number of particles which interact primarily, but not exclusively, through the electromagnetic field. The problem of understanding the linkages and couplings in multi-scale processes is a frontier problem of modern science involving fields as diverse as plasma phenomena in the laboratory to galactic dynamics.Unlike the first three states of matter, plasma, often called the fourth state of matter, involves the mesoscale and its interdisciplinary founding have drawn upon various subfields of physics including engineering, astronomy, and chemistry. Basic plasma research is now posed to provide, with major developments in instrumentation and large-scale computational resources, fundamental insights into the properties of matter on scales ranging from the atomic to the galactic. In all cases, these are treated as mesoscale systems. Thus, basic plasma research, when applied to the study of astrophysical and space plasmas, recognizes that the behavior of the near-earth plasma environment may depend to some extent on the behavior of the stellar plasma, that may in turn be governed by galactic plasmas. However, unlike laboratory plasmas, astrophysical plasmas will forever be inaccessible to in situ observation. The inability to test concepts and theories of large-scale plasmas leaves only virtual testing as a means to understand the universe. Advances in in computer technology and the capability of performing physics first principles, fully three-dimensional, particle-in-cell simulations, are making virtual testing a viable alternative to verify our predictions about the far universe.The first part of this paper explores the dynamical and fluid properties of the plasma state, plasma kinetics, and the radiation emitted from plasmas. The second part of this paper outlines the formulation for the particle-in-cell simulation of astrophysical plasmas and advances in simulational techniques and algorithms, as-well-as the advances that may be expected as the computational resource grows to petaflop speed/memory capabilities.Dedicated to the memories of Hannes Alfvén and Oscar Buneman; Founders of the Subject. 相似文献
15.
In this work, we consider the formation of electrostatic, dust-acoustic solitary structure in a unmagnetized plasma with Lorentzian electrons (kappa-distributed) and more than one species of thermal ions (Maxwellian). The work is inspired by results of different space-based observations of electrostatic solitary waves (ESW) in the near-earth and magnetospheric plasmas and recent experimental realization of existence of superthermal electron component in various space plasmas. We have, in this work, shown that existence of compressive potential structure is possible only with more than one species of thermal ions. Besides, formation of compressive double layers is also possible which depends on the amount of deviation of the electron thermal velocities from a Maxwellian distribution. We show that both dust-temperature and super-thermal electrons lead to a decrease in the soliton amplitude. 相似文献
16.
Padma K. Shukla 《Astrophysics and Space Science》1998,264(1-4):235-245
The status of waves and instabilities in magnetized dusty plasmas is summarized. The effects of an external magnetic field
on low-frequency electrostatic and electromagnetic waves in dusty plasmas are discussed. The kinetic and hydrodynamic instabilities
are shown to excite magnetized dusty plasma waves. The presence of the latter can give rise to an oscillatory wake-potential
which can be responsible for the charged dust grain attraction. The relevance of our investigation to laboratory and space
plasmas has been pointed out.
This revised version was published online in July 2006 with corrections to the Cover Date. 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.
F. Verheest M. A. Hellberg G. J. Gray R. L. Mace 《Astrophysics and Space Science》1996,239(1):125-139
Acoustic solitons are investigated in electron-positron plasmas containing equal hot and cool components of both species. The hot components are isothermal Boltzmann distributed, the cool constituents are modelled by adiabatic fluids. The equations are integrated exactly in terms of a Sagdeev potential. Solitons are shown to be possible, but no double layers, due to the symmetry in the model. Bearing in mind the constraints imposed by the Boltzmann assumption, small amplitude solitons only are found. Such findings are relevant for different kinds of astrophysical plasmas, as well as for other types of similar acoustic solitons. 相似文献
19.
We present the main findings of two recent studies using high-resolution MHD simulations of supersonic magnetized shear flow layers. First, a strong large-scale coalescence effect partially countered by small-scale reconnection events is shown to dominate the dynamics in a two-dimensional layer subject to Kelvin-Helmholtz (KH) instabilities. Second, an interaction mechanism between two different types of instabilities (KH and current-driven modes) is shown to occur in a cylindrical jet configuration embedded in an helical magnetic field. Finally, we discuss the implications of these results for astrophysical jets survival. 相似文献
20.
The influence of non-thermal Dupree turbulence and the plasma shielding on the electron–ion collision is investigated in astrophysical non-thermal Lorentzian turbulent plasmas. The second-order eikonal analysis and the effective interaction potential including the Lorentzian far-field term are employed to obtain the eikonal scattering phase shift and the eikonal collision cross section as functions of the diffusion coefficient, impact parameter, collision energy, Debye length and spectral index of the astrophysical Lorentzian plasma. It is shown that the non-thermal effect suppresses the eikonal scattering phase shift. However, it enhances the eikonal collision cross section in astrophysical non-thermal turbulent plasmas. The effect of non-thermal turbulence on the eikonal atomic collision cross section is weakened with increasing collision energy. The variation of the atomic cross section due to the non-thermal Dupree turbulence is also discussed. 相似文献