共查询到20条相似文献,搜索用时 2 毫秒
1.
R. Paul Drake 《Astrophysics and Space Science》2005,298(1-2):49-59
This paper explores the variations in radiative shock behavior originating from the properties of the system containing the
shock. Specifically, the optical depth of the upstream region and the downstream region both affect the behavior of radiative
shocks. Optically thick systems such as stellar interiors or supernovae permit only limited shock-induced increases in density.
At the other limit, the radiation and shock dynamics in optically thin systems permits the post-shock density to reach arbitrarily
large values. The theory of the shock structure is summarized for systems in which the upstream region is optically thin,
common to some astrophysical systems and a number of experiments. 相似文献
2.
V. I. Sotnikov H. Ruhl R. Presura T. Cowan J. N. Leboeuf P. Hellinger P. Travnicek 《Astrophysics and Space Science》2005,298(1-2):369-374
The problem of producing collisionless shocks in the laboratory is of great interest for space and astrophysical plasmas.
One approach is based on the idea of combining strong magnetic field (up to 100 Tesla) created during a Z-pinch discharge
with a plasma flow produced in the process of the interaction of a laser pulse with a solid target. In support of laboratory
experiments we present hybrid simulations of the interaction of the plasma flow with frozen in it magnetic field, with the
spherical obstacle. Parameters of the flow correspond to a laser plasma ablation produced in the laboratory during irradiation
of the target by a 3 J laser. Magnetic fields in the plasma flow and around the obstacle are created by the currents produced
by the pulse power ZEBRA voltage generator. With the appropriate set of initial conditions imposed on the flow collisionless
shocks can be created in such a system. Using independent generators for plasma flow and magnetic field allows for the exploration
of a wide range of shock parameters. We present simulations of the formation of supercritical collisionless shock relevant
to the experiment, performed with the 2D version of the hybrid code based on the CAM-CL algorithm [Planet. Space Sci. 51,
649, 2003]. 相似文献
3.
Laboratory experiments using a plasma wind generated by laser-target interaction are proposed and analyzed to investigate
the creation of a shock in front of the magnetosphere and the dynamo mechanism. The proposed experiments and simulations are
thought to be relevant to understanding the electron acceleration mechanisms at work in shock-driven magnetic dipole confined
plasma in compact magnetized stars. 相似文献
4.
C. Courtois R. A. D. Grundy A. D. Ash D. M. Chambers R. O. Dendy K. G. Mcclements N. C. Woolsey 《Astrophysics and Space Science》2005,298(1-2):93-98
Results from a scaled, collision-free, laser-plasma experiment designed to address aspects of collisionless plasma interaction
in a high-plasma β supernova remnant (SNR) are discussed. Ideal magneto-hydrodynamic scaling indicates that the experimental
plasma matches the SNR plasma at 500 ps. Experimental data show that the magnetic field can alter the plasma density profile
when two similar plasmas interact in a colliding geometry. These results are not explained by magnetic-field pressure; they
do, however, suggest magnetic field penetration that localizes the plasma particles to the Larmor radius, which appears smaller
than the size of the experiment and the particle mean-free paths and may thus increase the effective collisionality of the interacting plasma system. 相似文献
5.
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
6.
The main goals of experimental simulation in the laboratory of a planetary atmosphere are to feed the theoretical models,
and to help the treatment of observations. This type of simulation permits the direct study of objects that space missions
can't study or have not studied yet, through the production of laboratory analogues of gaseous or solid phases. But the representativity
of these laboratory analogues is of crucial importance.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
8.
空间无碰撞激波的数值研究 总被引:2,自引:0,他引:2
无碰撞激波是空间等离子体和宇宙等离子体中的重要物理现象。文中评述了数值研究空间无碰撞激波的两种方法-粒子模拟和混合模拟,给出了准垂直和准平行无碰撞激波的数值研究结果。还指出了一些尚未解决的研究问题。 相似文献
9.
Ikkoh Funaki Hidenori Kojima Hiroshi Yamakawa Yoshinori Nakayama Yukio Shimizu 《Astrophysics and Space Science》2007,307(1-3):63-68
To propel a spacecraft in the direction leaving the Sun, a magnetic sail (MagSail) blocks the hypersonic solar wind plasma
flow by an artificial magnetic field. In order to simulate the interaction between the solar wind and the artificially deployed
magnetic field produced around a magnetic sail spacecraft, a laboratory simulator was designed and constructed inside a space
chamber. As a solar wind simulator, a high-power magnetoplasmadynamic arcjet is operated in a quasisteady mode of 0.8 ms duration.
It can generate a simulated solar wind that is a high-speed (above 20 km/s), high-density (1018 m−3) hydrogen plasma plume of ∼0.7 m in diameter. A small coil (2 cm in diameter), which is to simulate a magnetic sail spacecraft
and can obtain 1.9-T magnetic field strength at its center, was immersed inside the simulated solar wind. Using these devices,
the formation of a magnetic cavity (∼8 cm in radius) was observed around the coil, which indicates successful simulation of
the plasma flow of a MagSail in the laboratory. 相似文献
10.
11.
C. Michaut T. Vinci L. Boireau M. Koenig S. Bouquet A. Benuzzi-Mounaix N. Osaki G. Herpe E. Falize B. Loupias S. Atzeni 《Astrophysics and Space Science》2007,307(1-3):159-164
This paper deals with the radiative shock from both theoretical and numerical points of view. It is based on the whole experimental
results obtained at Laboratoire d'Utilisation des Lasers Intenses (LULI, école Polytechnique). Radiative shocks are high-Mach
number shocks with a strong coupling between radiation and hydrodynamics which leads to a structure governed by a radiative
precursor. These shocks are involved in various astrophysical systems: stellar accretion shocks, pulsating stars, interaction
between supernovae and the interstellar medium. In laboratory, these radiative shocks are generated using high power lasers.
New diagnostics have been implemented to study the geometrical shape of the shock and the front shock density. Data were obtained
varying initial conditions for different laser intensities and temperature. The modeling of these phenomena is mainly performed
through numerical simulations (1D and 2D) and analytical studies. We exhibit results obtained from several radiative hydrodynamics
codes. As a result, it is possible to discuss about the influence of the geometry and physical parameters introduced in the
1D and 2D models. 相似文献
12.
T. Vinci M. Kœnig A. Benuzzi-Mounaix L. Boireau S. Bouquet S. Leygnac C. Michaut C. Stehlé O. Peyrusse D. Batani 《Astrophysics and Space Science》2005,298(1-2):333-336
This paper presents some recent measurements on radiative shocks generated in a xenon gas cell using high power laser. We
show new results on temperature and electronic density, and on radial expansion of the shock at various initial conditions
(laser energy and gas pressure). The data obtained are compared with one-dimensional and two-dimensional hydro simulations. 相似文献
13.
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
14.
An important contribution to the thermalization of the solar wind ions at the Earth's bow shock for high Mach numbers comes from the reflection of a fraction of these ions from the shock. Previous studies have examined the trajectories of the reflected ions assuming the shock to be an infinite plane. In this paper a model is developed to describe the trajectories of particles after reflection for a variety of shock geometries. Of particular interest are the initial conditions which allow the particle to return to the shock with a greater normal velocity than at first encounter, or to return to the shock at all. The effects of the magnetic field direction and the curvature of the shock on particle trajectories are discussed for cylindrical and spherical shock geometries and compared to those for a planar shock. 相似文献
15.
We present results from a global simulation of the interaction of the solar wind with Earth's magnetosphere, ionosphere, and
thermosphere for the Bastille Day geomagnetic storm and compare the results with data. We find that during this event the
magnetosphere becomes extremely compressed and eroded, causing 3 geosynchronous GOES satellites to enter the magnetosheath
for an extended time period. At its extreme, the magnetopause moves at local noon as close as 4.9 R
E to Earth which is interpreted as the consequence of the combined action of enhanced dynamic pressure and strong dayside reconnection
due to the strong southward interplanetary magnetic field component B
z, which at one time reaches a value of −60 nT. The lobes bulge sunward and shield the dayside reconnection region, thereby
limiting the reconnection rate and thus the cross polar cap potential. Modeled ground magnetic perturbations are compared
with data from 37 sub-auroral, auroral, and polar cap magnetometer stations. While the model can not yet predict the perturbations
and fluctuations at individual ground stations, its predictions of the fluctuation spectrum in the 0–3 mHz range for the sub-auroral
and high-latitude regions are remarkably good. However, at auroral latitudes (63° to 70° magnetic latitude) the predicted
fluctuations are slightly too high.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014228230714 相似文献
16.
The influences of the shock thickness and Alfven waves on the particle acceleration by diffusive shock waves are numerically studied through solving one-dimensional diffusive equation including the second-order Fermi effect. It is shown that the spectral index of the energetic particles strongly depends on the shock thickness. For example, the spectral index increases from 2.1 to 3.7 in the low energy range of 3—10 MeV and from 2.5 to 5.0 in the high energy range of 20—60 MeV as the thickness increases. The spectral index decreases from 4.3 to 3.1 as the particle injection energy increases. The spectral index decreases from 4.0 to 1.8 at the quasi-steady stage with the enhancement of the compression ratio from 2 to 4. The results indicate that under the influence of Alfven waves, the energetic particle spectrum at lower energy becomes flat and the spectral index decreases from 2.5 to 0.6 in the low energy range of 3—10 MeV and from 11.6 to 5.0 in the high energy range of 20—60 MeV. At the same time, the turning point energy reaches 19.6 MeV. The spectral index decreases from 5.8 to 2.9 as the energy density of Alfven waves increases. All these results are basically consistent with the theoretical models, as well as the observations of typical energetic particle events. 相似文献
17.
D. J. Ampleford S. V. Lebedev A. Ciardi S. N. Bland S. C. Bott G. N. Hall N. Naz C. A. Jennings M. Sherlock J. P. Chittenden A. Frank E. Blackman 《Astrophysics and Space Science》2007,307(1-3):51-56
Collimated flows ejected from young stars are believed to play a vital role in the star formation process by extracting angular
momentum from the accretion disk. We discuss the first experiments to simulate rotating radiatively cooled, hypersonic jets
in the laboratory. A modification of the conical wire array $z$-pinch is used to introduce angular momentum into convergent
flows of plasma, a jet-forming standing shock and into the jet itself. The rotation of the jet is evident in laser imaging
through the presence of discrete filaments which trace the rotational history of the jet. The presence of angular momentum
results in a hollow density profile in both the standing conical shock and the jet. 相似文献
18.
E. Martínez-Gómez H. J. Durand-Manterola H. Pérez de Tejada 《Astrophysics and Space Science》2007,310(3-4):211-230
A model is presented to describe the energization of charged particles in planetary magnetospheres. The model is based on
the stochastic acceleration produced by a random electric field that is induced by the magnetic field fluctuations measured
within the magnetospheres. The stochastic behavior of the electric field is simulated through a Monte Carlo method. We solve
the equation of motion for a single charged particle—which comprises the stochastic acceleration due to the stochastic electric
field, the Lorentz acceleration (containing the local magnetic field and the corotational electric field) and the gravitational
planetary acceleration of the particle—under several initial conditions. The initial conditions include the ion species and
the velocity distribution of the particles which depends on the sources they come from (solar wind, ionospheres, rings and
satellites). We applied this model to Saturn’s inner magnetosphere using a sample of particles (H+, H2O+, N+, O+ and OH+) initially located on Saturn’s north pole, above the C-Ring, on the south pole of Enceladus, in the north pole of Dione and
above the E-Ring. The results show that the particles tend to increase the value of their energy with time reaching several
eV in a few seconds and the large energization is observed far from the planet. We can distinguish three main energization
regions within Saturn’s inner magnetosphere: minimum (Saturn’s ionosphere), intermediate (Dione) and high-energy (Enceladus
and the E-ring). The resulting energy spectrum follows a power-law distribution (>1 keV), a logistic, an exponential decay
or an asymmetric sigmoidal (<1 keV). 相似文献
19.
D. J. Ampleford S. V. Lebedev A. Ciardi S. N. Bland S. C. Bott J. P. Chittenden G. Hall C. A. Jennings J. Armitage G. Blyth S. Christie L. Rutland 《Astrophysics and Space Science》2005,298(1-2):241-246
Whilst observations provide many examples of collimated outflows or jets from astrophysical bodies, there remain unresolved
questions relating to their formation, propagation and stability. The ability to form scaled jets in the laboratory has provided
many useful insights. Experiments (Lebedev et al.: 2002, ApJ 564, 113) using conical arrays of fine metallic wires on the MAGPIE generator (1MA in 240 ns) have produced radiatively cooled
collimated jets in vacuum using the redirection of convergent flows by a conical shock. Here we present results of a jet produced
by this method propagating through a photo-ionized, quasi-stationary gas cloud. A working surface is observed at the head
of the jet. The velocity of this working surface is lower than the velocity of a jet tip in vacuum. 相似文献