共查询到20条相似文献，搜索用时 46 毫秒
1.
The ZaP sheared-flow Z-pinch produces high density Z-pinch plasmas that are stable for up to 2000 times the classical instability times. The presence of an embedded radial shear in the axial flow is correlated with the observed stability, and is in agreement with numerical predictions of the stability threshold. The case is made that using a higher-Z working gas will produce supersonic plasma jets, consistent with dimensionless similarity constraints of astrophysical jets. This would allow laboratory testing of some regimes of astrophysical jet theory, computations, and observations. 相似文献
2.
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
3.
For the laboratory astrophysics community,those spectroscopic modeling codes extensively used in astronomy,e.g.Chianti,AtomDB,Cloudy and Xstar,cannot be directly applied to analyzing laboratory measurements due to their discrepancies from astrophysical cases.For example,plasma from an electron beam ion trap has an electron energy distribution that follows a Gaussian profile,instead of a Maxwellian one.The laboratory miniature for a compact object produced by a laser-driven implosion shows a departure from equilibrium,that often occurs in celestial objects,so we setup a spectral analysis system for astrophysical and laboratory(sasal) plasmas to act as a bridge between them,which benefits the laboratory astrophysical community. 相似文献
4.
A short summary of recent progress in measuring and understanding turbulence during magnetic reconnection in laboratory plasmas
is given. Magnetic reconnection is considered as a primary process to dissipate magnetic energy in laboratory and astrophysical
plasmas. A central question concerns why the observed reconnection rates are much faster than predictions made by classical
theories, such as the Sweet–Parker model based on MHD with classical Spitzer resistivity. Often, the local resistivity is
conjectured to be enhanced by turbulence to accelerate reconnection rates either in the context of the Sweet–Parker model
or by facilitating setup of the Pestchek model. Measurements at a dedicated laboratory experiment, called MRX or Magnetic
Reconnection Experiment, have indicated existence of strong electromagnetic turbulence in current sheets undergoing fast reconnection.
The origin of the turbulence has been identified as right-hand polarized whistler waves, propagating obliquely to the reconnecting
field, with a phase velocity comparable to the relative drift velocity. These waves are consistent with an obliquely propagating
electromagnetic lower-hybrid drift instability driven by drift speeds large compared to the Alfven speed in high-beta plasmas.
Interestingly, this instability may explain electromagnetic turbulence also observed in collisionless shocks, which are common
in energetic astrophysical phenomena. 相似文献
5.
V. A. Urpin 《Astrophysics and Space Science》1981,79(1):11-24
Hydrodynamical equations for a fully ionized hydrogen-helium plasma are derived by the Chapman-Enskog method. The electron and ion transport coefficients are found as the functions of electron and ion temperatures and number densities as well as of the magnetic field strength. The presented equations are needed for describing transport phenomena in laboratory and cosmic plasmas. It is shown that transport phenomena can produce abundance anomalies; e. g., a sound wave propagating through a homogeneous plasma may be accompanied by the oscillations of chemical composition. Various astrophysical consequences of the theory are discussed. 相似文献
6.
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
7.
I. M. Hall T. Durmaz R. C. Mancini J. E. Bailey G. A. Rochau 《Astrophysics and Space Science》2011,336(1):189-194
New, high spectral resolution X-ray observations from astrophysical photoionised plasmas have been recorded in recent years
by the Chandra and XMM-Newton orbiting telescopes. These observations provide a wealth of detailed information and have motivated
new efforts at developing a detailed understanding of the atomic kinetics and radiation physics of photoionised plasmas. The
Z facility at Sandia National Laboratories is a powerful source of X-rays that enables us to produce and study photoionised
plasmas in the laboratory under well characterised conditions. We discuss a series of radiation-hydrodynamic simulations to
help understand the X-ray environment, plasma hydrodynamics and atomic kinetics in experiments where a collapsing wire array
at Z is used as an ionising source of radiation to create a photoionised plasma. The numerical simulations are used to investigate
the role that the key experimental parameters have on the photoionised plasma characteristics. 相似文献
8.
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
9.
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
10.
P. P. Malovichko 《Kinematics and Physics of Celestial Bodies》2014,30(5):223-233
The behavior of dispersive Alfven waves (DAWs) in astrophysical plasmas of finite and high pressure, which have not been considered thus far, is studied in the hydrodynamic approximation. The results are analyzed and compared with those obtained in the kinetic approach. It is shown that one general solution for DAWs in plasmas of finite and high pressure can be obtained using the hydrodynamic approach in contrast to the kinetic one. Kinetic and hydrodynamic solutions correspond to each other very well in a domain with weakly damped DAWs; however, solutions may differ appreciably in some parameter domains, especially in high-pressure plasma. The effect of parameters of the astrophysical medium on the DAW behavior and properties is analyzed. All the main wave characteristics were determined: dispersion, damping, polarization, density perturbations, and charge density perturbations. Since finite-pressure plasma is one of the most frequently encountered states of astrophysical plasma, it is very important to take into account specific features in behavior of these waves for their detecting and a more correct understanding of their behavior and the role they play in different astrophysical processes that occur in space environment. 相似文献
11.
The positron acoustic shock and solitary wave are explored in nonextensive electron-positron-ion plasma. The plasma system under-consideration, consists of a classical positron beam, q distributed electrons and positively charged bulky ions constitute a neutralizing background. The nonlinear Korteweg-de Vries and Burger equations are derived by employing the standard reductive perturbation method. The positron acoustic wave in linear limit is also discussed for dissipative as well as nondissipative cases of nonextensive plasmas. The plasma parameters such as, the concentration of neutralizing ions background, beam velocity, temperature and q parameter of the nonextensive electrons are noticed to significantly affect the positron acoustic shock and solitary waves. Our findings may be helpful in the understanding of laboratory beam plasma interaction experiments as well as the astrophysical nonextensive plasmas interacting with positron beam. 相似文献
12.
D. B. Melrose 《Astrophysics and Space Science》1996,242(1-2):209-246
Acceleration processes for fast particles in astrophysical and space plasmas are reviewed with emphasis on stochastic acceleration by MHD turbulence and on acceleration by shock waves. Radiation processes in astrophysical and space plasmas are reviewed with emphasis on plasma emission from the solar corona and electron cyclotron maser emission from planets and stars. 相似文献
13.
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
14.
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
15.
M. Akbari-Moghanjoughi 《Astrophysics and Space Science》2012,337(2):613-622
Using the extended Poincaré-Lighthill-Kuo (PLK) reductive perturbation method, which incorporates the phase-shift variations,
it is shown that common features on propagation and head-on collisions of ion-acoustic waves exist for a magnetized plasmas
of different inertial-less particle distributions. For instance it is remarked that, the soliton amplitude is always independent
of magnetic field strength while strictly depends on its angle regarding the propagation direction. Both types of solitons
(compressive or rarefactive) are shown to exist which are defined through the critical angle γ=π/2 or other critical values depending on plasma fractional parameters. These critical plasma parameter values also define
the sign of head-on collision phase shift. Furthermore, it is proved that for a given set of plasma parameters there is always
a relative angle of propagation regarding to that of the magnetic-field for which the soliton width is maximum. Current findings
apply to a wide range of magnetized plasmas including those containing background dust ingredients or two-temperature inertial-less
particles and may be used to study laboratory or astrophysical magnetoplasmas. 相似文献
16.
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
17.
D. B. Melrose 《Astrophysics and Space Science》1968,2(2):171-235
A semiclassical theory describing the emission and absorption of waves is applied to the interaction of charged particles with waves in magnetized plasmas. Spontaneous emission of all cold plasma wave modes is calculated in detail. The method gives the absorption coefficient for the waves and a diffusion equation in momentum space for the particles describing the effects of the induced processes.Coefficients describing the systematic change of particle parameters follow from the diffusion equation. Applications of astrophysical interest are outlined. 相似文献
18.
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
19.
Mikhail V. Medvedev 《Astrophysics and Space Science》2007,307(1-3):245-250
It has recently been realized that the Weibel instability plays a major role in the formation and dynamics of astrophysical
shocks of gamma-ray bursts and supernovae. Thanks to technological advances in the recent years, experimental studies of the
Weibel instability are now possible in laser-plasma interaction devices. We, thus, have a unique opportunity to model and
study astrophysical conditions in laboratory experiments – a key goal of the Laboratory Astrophysics program. Here we briefly
review the theory of strong non-magnetized collisionless GRB and SN shocks, emphasizing the crucial role of the Weibel instability
and discuss the properties of radiation emitted by (isotropic) electrons moving through the Weibel-generated magnetic fields,
which is referred to as the jitter radiation. We demonstrate that the jitter radiation field is anisotropic with respect to
the direction of the Weibel current filaments and that its spectral and polarization characteristics are determined by microphysical
plasma parameters. We stress that the spectral analysis can be used for accurate diagnostics of the plasma conditions in laboratory
experiments and in astrophysical GRB and SN shocks. 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